Efficient perovskite solar cells via improved carrier management

Polar Three-dimensional Organic-inorganic Hybrid Perovskite Realize Highly Sensitive Self-driven Ultraviolet Photodetection

Bulk photovoltaic effect (BPVE) triggered by spontaneous polarization in polar organic-inorganic hybrid perovskites (OIHPs) has brought unprecedented development opportunities for self-powered ultraviolet photodetection. However, the currently reported ultraviolet optoelectronic devices are dominated by low-dimensional hybrid perovskites, in which low carrier mobility limits the photoelectric conversion efficiency. Herein, we report for the first time a polar three-dimensional OIHPs, namely MHyPbBr3 (1, MHy=methylhydrazine), that achieves high-performance self-driven ultraviolet photodetection. Benefitting from the large spontaneous polarization and excellent semiconductor attributes, 1 exhibits 0.33 V BPVE and high carrier mobility lifetime product (μτ) of 1.972×10-3 cm-2 V-1 under ultraviolet illumination. Notably, such merits contribute to efficient self-driven photodetection, where responsivity (R) and detectivity (D*) reach up to 198 mA W-1 and 1.42×1013 Jones, surpassing most reported ultraviolet photodetectors. Furthermore, based on the reversible phase transition of 1, we have achieved controllable ultraviolet photoelectric detection. This work will shed light on the fabrication of high-response self-driven ultraviolet optoelectronic devices.

Achieving >23% Efficiency Perovskite Solar Minimodules with Surface Conductive Coordination Polymer

Despite the reported high efficiencies of small-area perovskite photovoltaic cells, the deficiency in large-area modules has impeded the commercialization of perovskite photovoltaics. Enhancing the surface/interface conductivity and carrier-transport in polycrystalline perovskite films presents significant potential for boosting the efficiency of perovskite solar modules (PSMs) by mitigating voltage losses. This is particularly critical for multi-series connected sub-cell modules, where device resistance significantly impacts performance compared to small-area cells. Here, an effective approach is reported for decreasing photovoltage loss through surface/interface modulation of perovskite film with a surface conductive coordination polymer. With post-treatment of meso-tetra pyridine porphyrin on perovskite film, PbI2 on perovskite film reacts with pyridine units in porphyrins to generate an iso-structural 2D coordination polymer with a layered surface conductivity as high as 1.14 × 102 S m-1, due to the effect of surface structure reconstruction. Modified perovskite film exhibits greatly increased surface/interface conductivity. The champion PSM obtains a record efficiency up to 23.39% (certified 22.63% with an aperture area of 11.42 cm2) featuring only 0.33-volt voltage loss. Such a modification also leads to substantially improved operational device stability.

Buried Interface Regulation with a Supramolecular Assembled Template Enables High-Performance Perovskite Solar Cells for Minimizing the VOC Deficit

Despite the rapid development of perovskite solar cells (PSCs) in the past decade, the open-circuit voltage (VOC) of PSCs still lags behind the theoretical Shockley-Queisser limit. Energy-level mismatch and unwanted nonradiative recombination at key interfaces are the main factors detrimental to VOC. Herein, a perovskite crystallization-driven template is constructed at the SnO2/perovskite buried interface through a self-assembled amphiphilic phosphonate derivative. The highly oriented supramolecular template grows from an evolutionary selection growth via solid-solid phase transition. This strategy induces perovskite crystallization into a highly preferred (100) orientation toward out-of-plane direction and facilitated carrier extraction and transfer due to the elimination of energy barrier. This self-assembly process positively passivates the intrinsic surface defects at the SnO2/perovskite interface through the functionalized moieties, a marked contrast to the passive effect achieved via incidental contacts in conventional passivation methods. As a result, PSCs with buried interface modification exhibit a promising PCE of 25.34%, with a maximum VOC of 1.23 V, corresponding to a mere 0.306 V deficit (for perovskite bandgap of 1.536 eV), reaching 97.2% of the theoretical VOC limit. This strategy spontaneously improves the long-term operational stability of PSCs under thermal and moisture stress (ISOS-L-3: MPP, 65 °C, 50% RH, T92 lifetime exceeding 1200 h).

Discovering novel lead-free mixed cation hybrid halide perovskites via machine learning

In our recent study (S. Alidoust, F. Jamalinabijan and A. Tekin, ACS Appl. Energy Mater., 2024, 7, 785-798), a thorough computational screening using density functional theory (DFT) was conducted on mixed cation halide perovskites with a general formula of AA'BX3, aiming to identify promising lead-free candidates. Employment of 23 A/A'-cations, 29 B-ions, and 4 X-anions yielded approximately 29 000 possible perovskite combinations. However, while modern high-throughput DFT frameworks can handle large-scale calculations, treating the entire configurational space of 29 000 possible perovskite combinations remains computationally demanding. Leveraging machine learning (ML) approaches could provide a more efficient alternative for capturing this complexity. Therefore, by using two empirical criteria known as octahedral and tolerance factors, this huge number was narrowed to nearly 2700, and the corresponding decomposition energy and band gap calculations were performed for each one of them. However, the remaining nearly 26 300 perovskites, though not selected by the empirical criteria, could still hold valuable and potentially promising candidates. Therefore, an ML model has been trained on the DFT-calculated subset, which has been increased to 4181 to achieve molecular and elemental homogeneity in these data sets to predict and identify promising perovskites within the unexamined portion of the dataset. Remarkably, the ML approach identified 930 promising perovskites satisfying both the decomposition energy (≤0.025 eV per atom) and band gap (1.0 ≤ gap ≤ 2.0 eV) criteria. Among these, 20 perovskites were selected for further validation through DFT calculations, and a very nice agreement has been obtained between the predicted and calculated decomposition energy and band gap values. These findings highlight the effectiveness of ML in accelerating the discovery of materials with specific desirable properties.

Tunable Dimensionality and Emission of Organic Metal Halides by Denser Stacking of Pb-Br Polyhedra

Organic metal halides (OMHs) have attracted extensive research interests due to their interesting photoluminescent properties. However, to date, most OMHs have been synthesized through the trial-and-error method, and it remains a big challenge to control the molecular-level structures through directed synthetic approaches to rationally optimize luminescence properties. In this work, we proposed a crystal structure modulation strategy to control the dimensionality and optical properties of OMHs by increasing the packing density of Pb-Br octahedra via altering the precursor stoichiometry. By precisely adjusting the ratio of 3-aminomethylpyridine to PbBr2 in the initial reactants, (C6N2H10)2PbBr6 (0D-J1) with a 0D structure, (C6N2H10)PbBr6 (2D-J2) with a 2D structure, and C3NH5PbBr (3D-J3) with a 3D structure were successfully synthesized. 0D-J1 exhibits a bright broadband yellow emission with a photoluminescence quantum yield (PLQY) of 35.40%. 2D-J2 shows a free exciton narrowband emission at room temperature and self-trapped excitons (STEs) emission at low temperatures. 3D-J3 displays a permanent defect state broad emission at room temperature. Additionally, the synthesis of compounds from the T series and P series with different dimensionalities further verifies the general applicability of this strategy. This strategy enables the directed control of the structure and optical properties of LD-OMHs while preserving the functionality of organic cations, and paves an avenue for designing and synthesizing LD-OMHs with functional coordination between organic cations and inorganic polyhedra. Together with the efficient emission and outstanding stability of 0D-J1, a high-performance white-light emitting diode (WLED) with a high color rendering index (CRI) of 92 is demonstrated.

Optimizing UV Resistance and Defect Passivation in Perovskite Solar Cells with Tailored Tin Oxide

Tin oxide (SnO2) as an electron transport layer (ETL) has garnered significant attention in planar perovskite solar cells (PSCs) for its excellent physical and chemical properties, paving its commercial potential. However, its drawbacks, such as surface defects and photocatalytic properties due to its wide band gap, remain unresolved. Under ultraviolet (UV) light, photocatalytic SnO2 induces perovskite phase transitions at the interface, compromising device stability. In this study, the fluorescent dopant sodium 2,2'-([1,1'-Biphenyl]-4,4'-Diylbis (Ethene-2,1-Diyl)) Dibenzenesulfonate (CF351) is introduced into SnO2 Solution for the first time. With excellent UV absorption, CF351 effectively blocks UV light, reducing SnO2-induced perovskite degradation. Perovskite films on CF351-doped SnO2 show remarkable stability under continuous UV irradiation (365 nm) for 32 days, the resistance to phase transition is improved by 100%. PSCs retaining 80.8% of their initial power conversion efficiency (PCE) after ≈1000 h of UV exposure, compared to only 18.7% for control. Additionally, CF351 passivates interfacial defects, regulates crystallization, and optimizes energy levels. It's down-conversion capability also enhances photocurrent by generating extra visible photons. As a result, CF351-doped PSCs achieve a PCE of 22.59%, significantly surpassing the 20.42% of control devices. This work provides an effective strategy for preparing highly efficient and UV stable PSCs.

Reduction of Nonradiative Recombination at Perovskite/C60 Interface in Inverted Perovskite Solar Cells

Although p-i-n type inverted perovskite solar cells (PSCs) achieve excellent photoelectric efficiencies, the nonradiative recombination at the perovskite/C60 interface is still the key factor affecting the overall efficiency of p-i-n PSCs. Herein, a synergistic passivation strategy (meta-fluoro-phenylethylammonium iodide and piperazine iodide) is developed to modify the perovskite/C60 interface in p-i-n PSCs. This strategy facilitates in situ reconstruction of the perovskite film to obtain a smooth and flat perovskite surface. Furthermore, the two molecules work synergistically to passivate surface defects, adjust the interface energy levels, and bolster the interface electric field, all of which reduce the nonradiative recombination losses at the perovskite/C60 interface. The optimal PSCs adopting this strategy achieve a power conversion efficiency of 25.85%. (certified value of 25.22%). After operating at the maximum power point for 1000 h, the 95% initial efficiency can be maintained. Furthermore, this process is universally applicable and scalable.

A Soft Nonpolar-Soluble Two-Dimensional Perovskite for General Construction of Mixed-Dimensional Heterojunctions

Constructing mixed-dimensional heterojunctions through ion exchange between functional organic ammonium halides and the already-deposited bulk 3D perovskite films is a widely adopted strategy to effectively passivate and stabilize perovskite solar cells (PSCs). Such process poses challenges in precisely controlling the composition and distribution of the heterojunctions across the film, in particular for large-area applications. Here, a soft 2D perovskite based on tetrapheptyl-ammonium iodide (TPAI), noted as TPA2PbI4 is reported. It is the first-reported nonpolar readily soluble 2D perovskite, leading to highly compact and oriented perovskite layers. In addition, this nonpolar soluble TPA2PbI4 is beneficial to universally construct thickness-controllable mixed-dimensional perovskite heterojunctions to suppress the non-radiative recombination and promote charge-carrier transfer on all the FA-, MA- and CsPbI3 PSCs. Such a unique strategy is also suitable for upscaling fabrication, demonstrated by 30 cm × 30 cm FAPbI3 perovskite submodules with a certified efficiency of 22.06%.

Graphene-based thermoelectric materials: toward sustainable energy-harvesting systems

Among sustainable energy-harvesting systems, thermoelectric technology has attracted considerable attention because of its ability to directly convert heat into electricity and diverse applications. Graphene, with its exceptional electrical conductivity and mechanical properties, is a promising candidate for thermoelectric materials. However, efficient thermoelectric applications require materials with a high Seebeck coefficient and low thermal conductivity-criteria that graphene does not inherently satisfy, owing to its gapless energy band structure and ballistic thermal conduction. This review examines the thermoelectric properties of graphene, optimization strategies, and the potential of graphene hybridization for thermoelectric applications. To overcome the intrinsic limitations of graphene for thermoelectric utilization, nanostructuring strategies based on its synthesis methods are discussed. Furthermore, strategies for graphene hybridization are introduced, with a focus on maximizing thermoelectric efficiency through interactions with nanostructured materials of various dimensions. Finally, the potential of graphene-based thermoelectric materials and future research directions are discussed.

Discovery of Perovskite Cosolvency and Undoped FAPbI3 Single-Crystal Solar Cells Fabricated in Ambient Air

We report the cosolvency effect of formamidinium lead triiodide (FAPbI3) in a mixture of γ-butyrolactone (GBL) and 2-methoxyethanol (2ME), a phenomenon where FAPbI3 shows higher solubility in the solvent blend than in either alone. We found that FAPbI3 exhibits 10× higher solubility in 30% 2ME in GBL than in 2ME alone and 40% higher solubility than in GBL alone at 90 °C. This enhanced solubility is attributed to the disruption of the hydrogen bonding network within 2ME, allowing its hydroxyl and ether groups to interact more freely with the solute. Leveraging this phenomenon, we grew phase-stable α-FAPbI3 thin single crystals under ambient air conditions with no doping. Compared to conventional cesium-doped FAPbI3, the undoped FAPbI3 single-crystal films exhibited lower defect densities and enhanced charge retention and transfer while also avoiding phase segregation linked to cesium incorporation. Solar cells fabricated with these ambient-air-grown single-crystal films achieved an efficiency of 21.56% (17.72% for cesium-doped FAPbI3), retaining 90% of performance after six months of storage. These findings advance our understanding of perovskite solubility in solvent blends and offer an efficient pathway for producing stable, high-efficiency FAPbI3 single-crystal solar cells through ambient air fabrication, overcoming the limitations of doping.

The study of inorganic absorber layers in perovskite solar cells: the influence of CdTe and CIGS incorporation

The perovskite solar cell has been the subject of intense breakdown lately because of its exceptional efficiency. Nevertheless, they confront a significant challenge due to the absorber layer's (perovskite) sensitivity to oxygen and water, which can cause rapid material degradation and adversely affect the solar cell's performance. The commonly used organic hole transport layer (HTL), Spiro-OMeTAD, tends to degrade over time, exacerbating the issue. To address this challenge, two-stage research was conducted. Initially, the CH3NH3PbI3 thin film was experimentally prepared, and XRD analysis confirmed the material's satisfactory crystalline phase (tetragonal), with a crystal size of 73.9 nm. An energy band gap of 1.55 eV was obtained experimentally, demonstrating good correspondence with the literature. Then, perovskites with different crystal structures (cubic, tetragonal, and orthorhombic) were calculated by DFT. These calculations obtained energy band gaps with values of 1.5 eV for the cubic, 1.7 eV for the tetragonal, and 3.9 eV for the orthorhombic. Subsequently, a numerical simulation study using SCAPS was carried out to validate the theoretical performance of an experimental solar cell with Spiro-OMeTAD as the HTL. Also, a simulation without HTL was performed to highlight its importance. Finally, comparative studies were conducted to evaluate the feasibility of incorporating CdTe and CIGS as inorganic absorbing layers within perovskite solar cells (MAPI). The objective was to investigate their potential for cooperative behavior in light absorption and charge transport. The findings indicated that the CIGS absorbing layer outperformed both materials, achieving an efficiency of 15.67%. Furthermore, an optimization study for the CIGS layer was performed, resulting in enhanced output parameters, including a maximum efficiency of 28.32%. This research represents a significant advancement in developing stable and efficient perovskite solar cells.

Interface-oriented bridges toward efficient carbon-based perovskite solar cells

The perovskite/electron transport layer interface plays a critical role in perovskite solar cell (PSC) performance and stability. Here, we report potassium bisaccharate (PB) acting as a multifunctional interfacial chemical bridge at the interface between the electron transport layer and the perovskite layer on introducing it into a buried interface. The carboxyl group at one end of the molecule is anchored to the hydroxy-rich SnO2 surface through covalent interactions, stabilizing its out-of-plane orientation, and the carboxyl group at the other end reduces non-radiative recombination by passivating the under-coordinated Pb2+ in the perovskite. Sum-frequency generation (SFG) spectra confirm out-of-plane orientations and optimize energy level alignment. Carbon-based PSCs treated with PB achieve a champion PCE of 19.69% (active area: 0.04 cm2) and retain 95.8% of their initial efficiency after 1200 h under ambient conditions. These results demonstrate PB as a promising buried interface modifier to enhance efficiency and long-term stability in carbon-based PSCs.

Precise Anchoring of Pb-Based Defects for Efficient Perovskite Solar Cells: A Universal Strategy from Lab-Scale Small-Area Devices to Large-Area Modules

Solution-processed perovskite solar cells (PSCs) generally suffer from serious Pb-based defects, and the issue becomes more pronounced during the upscaling process. A universal strategy that bridges small-area devices and large-area modules is imperative for advancing PSC technology from the lab toward market readiness. Here, to effectively address the Pb-based defect proliferation issues of perovskite surfaces, an N,N-maleoyl-glycine (NMG) post-treatment anchoring strategy was proposed. Precise anchoring of Pb-based defects was achieved due to the strong Lewis acid-base interactions between NMG functional molecules and perovskites. Consequently, a relatively high power conversion efficiency (PCE) of 25.45% was achieved for the small-area devices, due to the greatly improved open-circuit voltage (Voc) and fill factor (FF). More importantly, impressive PCEs of 19.58% (with regular n-i-p configurations) and 18.75% (with inverted p-i-n configurations) were achieved for the large-area PSC modules with an active area of 64 cm2, confirming their compatibility with the upscaling process. Furthermore, the unencapsulated NMG-based devices maintain more than 90% of their initial PCE after continuous 1 sun illumination for 1000 h under maximum power point (MPP) tracking, demonstrating exceptional operational stability. Our achievements provided a universal and promising strategy for both small-area devices and large-area modules, thus potentially expediting their upscaling applications.

Understanding the Structural Dynamics of 2D/3D Perovskite Interfaces

The use of 2D perovskite capping layers to passivate the surface defects of 3D perovskite active layers has become ubiquitous in high performance lead halide perovskite solar cells. However, these 2D/3D interfaces can be highly dynamic, with the structure evolving to form various mixed dimensional phases when exposed to thermal stress or illumination. Changes in the photoluminescence spectrum of formamidinium lead iodide (FAPbI3) films capped with alkylammonium-based 2D perovskites as they age at 100 °C or under simulated 1 sun illumination indicate that the 2D perovskite transforms to progressively larger inorganic layer thicknesses (denoted by layer number n), eventually approaching a steady-state condition where only the 3D perovskite (n = ∞) is detectable. We find that this transformation slows by a factor of ∼2 when the length of the alkyl chain in the organic monoammonium ligand is increased from butylammonium to dodecylammonium. Furthermore, replacing dodecylammonium with its diammonium ligand counterpart, 1,12-dodecanediammonium, slows the structural transformation by 10-fold. These results point to the use of diammonium ligands as a possible pathway to form stable 2D/3D interfaces.

A 2D/3D Heterostructure Perovskite Solar Cell with a Phase-Pure and Pristine 2D Layer

Interface engineering plays a critical role in advancing the performance of perovskite solar cells. As such, 2D/3D perovskite heterostructures are of particular interest due to their optoelectrical properties and their further potential improvements. However, for conventional solution-processed 2D perovskites grown on an underlying 3D perovskite, the reaction stoichiometry is normally unbalanced with excess precursors. Moreover, the formed 2D perovskite is impure, leading to unfavorable energy band alignment at the interface. Here a simple method is presented that solves both issues simultaneously. The 2D formation reaction is taken first to completion, fully consuming excess PbI2. Then, isopropanol is utilized to remove excess organic ligands, control the 2D perovskite thickness, and obtain a phase-pure, n = 2, 2D perovskite. The outcome is a pristine (without residual 2D precursors) and phase-pure 2D perovskite heterostructure with improved surface passivation and charge carrier extraction compared to the conventional solution process. PSCs incorporating this treatment demonstrate a notable improvement in both stability and power conversion efficiency, with negligible hysteresis, compared to the conventional process.

Tin Oxide: The Next Benchmark Transport Material for Organic Solar Cells?

Organic solar cells (OSCs) are one of the most promising emerging photovoltaic technologies due to the rapid increase in efficiency in recent years. While efficiencies over 20% have been reported in laboratory scale devices using the conventional (p-i-n) structure, OSCs with inverted (n-i-p) structures still underperform, reaching values around 18%. Tin oxide (SnO2) has recently emerged as a promising transport layer for OSCs. Yet, some reproducibility challenges shown by the literature have hindered the full adaptation of this electron transport layer (ETL) by the organic solar cell community. This Perspective evaluates the current status of investigation for SnO2 as the transport layer for OSCs, focusing on its integration into state-of-the-art systems and highlighting the challenges toward its implementation. We examine which strategies lead to the most efficient and stable devices using SnO2 and give a critical view of whether this material can soon become the next benchmark electron transport layer for OSCs.

Pressure Engineering to Enable Improved Stability and Performance of Metal Halide Perovskite Photovoltaics

In this work, we demonstrate that an external pressure of 15-30 kPa can significantly improve metal halide perovskite (MHP) film thermal stability. We demonstrate this through the application of weight on top of an MHP film during thermal aging in preserving the perovskite phase and the mobile ion concentration, an effect which we hypothesize reduces the extent to which volatile species can escape from the MHP lattice. This method is shown to be effective for a more scalable approach by only applying the weight to a cover glass during the lamination of an epoxy-based resin, after which the weight is removed. The amount of pressure applied during lamination is shown to correlate with stability in both 1 sun illumination and damp heat testing. Lastly, the performance of MHP photovoltaic devices is improved using pressure during lamination, an effect which is attributed to improved interfacial contact between the MHP and the adjacent charge transport layers and healing of any voids or defects that may exist at the buried interface after processing. As such, there are implications for tuning the amount of pressure that is applied during lamination to enable the durability of MHP solar modules toward manufacturing-scale deployment.

Colloidal Ink Engineering for Slot-Die Processes to Realize Highly Efficient and Robust Perovskite Solar Modules

Perovskite solar cells (PSCs) have emerged as a promising alternative to silicon solar cells, but challenges remain in developing perovskite inks and processes suitable for large-scale production. This study introduces a novel approach using colloidal inks incorporating toluene and chlorobenzene as co-antisolvents for PSC fabrication via slot-die process. It is found that colloidal inks that are strategically engineered can significantly improve the rheological properties of perovskite inks, leading to enhanced wettability and high-quality film formation. The formation of large colloids such as α cubic perovskite, δ hexagonal perovskite and transition intermediate phases promotes heterogeneous nucleation and lowers activation energy for crystallization, resulting in superior crystal growth and improved film morphology. Notably, the co-solvent enhances the FA-PbI3 binding energy and weakens the dimethyl sulfoxide coordination, which is more thermodynamically favorable for perovskite crystallization. This colloidal strategy yields devices with a maximum efficiency of 21.32% and remarkable long-term stability, retaining 77% of initial efficiency over 10115 h. The study demonstrates the scalability of this approach, achieving 20.26% efficiency in lab-scale minimodules and 19.15% in larger convergence minimodules. These findings provide an understanding of the complex relationship between ink composition, rheological properties, film quality, crystallization kinetics, and device performance.

Gradient Thermal Annealing Assisted Perovskite Film Crystallization Regulation for Efficient and Stable Photovoltaic-Photodetection Bifunctional Device

Perovskite crystallization regulation is essential to obtain excellent film optoelectronic properties and device performances. However, rapid crystallization during annealing always results in poor perovskite film and easy formation of trap, thereby greatly restricting device performance due to severe non-radiative recombination. Here, an easy and reproducible gradient thermal annealing (GTA) approach is used to regulate the perovskite crystallization. Through a low-temperature initial annealing of GTA, the solvent evaporation is slowed down, thus extending nucleation time and providing a buffer for the rapid crystallization of perovskite grains in the subsequent high-temperature stage. As a result, completely converted and highly crystalline perovskite is obtained with 1.6 times larger grain size, reduced trap density and suppressed non-radiative recombination of photo-generated carriers. The film crystallinity is also enhanced with more advantageous (100) and (111) lattice facets which are favorable for carrier transport. Consequently, the perovskite photodetectors exhibit a large linear dynamic range of 174 dB and an excellent response even under ultra-weak light of 303 pW. Meanwhile, perovskite solar cells achieved increased PCE and maintained 85% of original efficiency after heating at 65 °C for nearly 1000 h under unencapsulated conditions. To the knowledge, this represents the best performance reported for a perovskite photovoltaic-photodetection bifunctional device.

Regulating Bifacial Surface Potential of Perovskite Film Enables Efficient Perovskite Solar Cells Universal for Different Charge Transport Layers

Planar perovskite solar cells (PSCs) show huge promise as an efficient photovoltaic technology, where the inefficient carrier transport at the hetero-interface largely limits their performance advancement. Herein, bifacial surface potential regulation is realized in a monolithic perovskite film through interface doping, leading to optimized dual-interfacial energy level alignment. In a n-i-p planar device, the up-shift of Fermi level on the perovskite bottom surface is first achieved through bottom-up diffusion of Li+. Then, vitamin D2 is incorporated into the methoxy-Phenethylammonium iodide (MeO-PEAI) passivator, which can neutralize the up-shift of the Fermi level of perovskite top surface induced by MeO-PEAI passivation and further induce its down-shift. Both experimental measurements and theoretical simulation reveal that the bifacial surface potential regulation effectively promotes interfacial carrier transport and reduces carrier recombination, enhancing the adaptability of efficient PSCs to different charge transport materials. Impressively, the PSCs with 2,2',7,7'-Tetrakis [N, N-di(4-methoxyphenyl) amino]-9,9'-spirobifluorene (Spiro-OMeTAD) and 2,4,6-Trimethyl-N, N-diphenylaniline (PTAA) achieve efficiencies of 26.05% (certificated 25.80%) and 24.65%, respectively. Besides, the device can maintain 99% of its highest efficiency after aging more than 2200 h in ambient air with a relative humidity of ≈20%, showing excellent stability.

Stress Relaxation for Lead Iodide Nucleation in Efficient Perovskite Solar Cells

Porous lead iodide (PbI2) film is crucial for the complete reaction between PbI2 and ammonium salts in sequential-deposition technology so as to achieve high crystallinity perovskite film. Herein, it is found that the tensile stress in tin (IV) oxide (SnO2) electron transport layer (ETL) is a key factor influencing the morphology and crystallization of PbI2 films. Focusing on this, lithium trifluoromethanesulfonate (LiOTf) is used as an interfacial modifier in the SnO2/PbI2 interface to decrease the tensile stress to reduce the necessary critical Gibbs free energy for PbI2 nuclei formation. The relaxed tensile stress facilitates the more porous PbI2 generation with larger particles and higher roughness, resulting in superior-quality perovskite films. Besides, this strategy effectively passivates the inherent electron traps of SnO2 and smooths the interfacial energy levels, boosting the charge extraction and transfer. As a result, a champion power conversion efficiency (PCE) of 25.33% (25.10% stabilized for 600 s) is achieved. Furthermore, the device demonstrates exceptional stability, retaining 90% of its initial PCE at its maximum power point tracking measurement (under 100 mW cm-2 white light illumination at ≈55 °C temperature, in N2 atmosphere) after 600 h.

Enhanced Efficiency and Stability of Tin Halide Perovskite Solar Cells Through MOF Integration

Tin halide perovskites are promising candidates for lead-free perovskite solar cells due to their ideal bandgap and high charge-carrier mobility. However, poor crystal quality and rapid degradation in ambient conditions severely limit their stability and practical applications. This study demonstrates that incorporating UiO-66, a zirconium-based MOF, significantly enhances the performance and stability of tin halide perovskite solar cells (TPSCs). The unique porous structure and abundant carboxylate groups of UiO-66 improve the crystallinity and film quality of FASnI₃, reduce defect density, and prolong charge carrier lifetimes. Consequently, the power conversion efficiency (PCE) of UiO-66-integrated TPSCs increases from 11.43% to 12.64%, and the devices maintain over 90% of their initial PCE after 100 days in a nitrogen glovebox. These findings highlight the potential of UiO-66 in addressing the efficiency and stability challenges of tin halide perovskites.

Multifunctional acetoacetanilide additive strategy for enhanced efficiency and stability in perovskite solar cells

Perovskite solar cells (PSCs) have garnered tremendous interest for their cost-effective solution-based fabrication process and impressive power conversion efficiency (PCE). The performance and stability of PSCs are closely tied to the quality of the perovskite film. Additive engineering has emerged as a highly effective strategy to achieve stable and efficient PSCs. In this study, acetoacetanilide (AAA), containing amide and carbonyl groups, is introduced for the first time as a multifunctional agent to the MAPbI3 precursor solution. Carbonyl groups in AAA coordinate with lead ions (Pb2+), influencing the crystallization process by binding to Pb2+ ions through lone pair electrons. It helps to control crystallization kinetics and passivates defects caused by under-coordinated Pb2+ ions. Simultaneously, the amide groups strongly interact with iodide ions (I-), stabilizing them and suppressing ion migration, which reduces defect vacancies in the perovskite structure. Incorporating AAA led to a significant improvement in PCE, increasing from 16.93% in the untreated device to 20.1% in the AAA-treated devices. Furthermore, the AAA-treated devices showed more stability behavior against humidity and light. These findings underscore the potential of AAA as a high-performing additive for advancing the PCE and stability of PSCs.

Hf Doping for Defect and Carrier Management in Magnetron-Sputtered Tin Oxide Electron Transport Layers for Perovskite Solar Cells

The performance of perovskite solar cells (PSCs) with magnetron-sputtered tin oxide (SnOx) electron transport layers (ETLs) is strongly influenced by the optical and electrical characteristics of the SnOx. However, magnetron-sputtered SnOx typically exhibits oxygen-vacancy (VO)-related point defects. This leads to significant interface charge recombination, which restricts both the open-circuit voltage (VOC) and fill factor (FF) of PSCs using SnOx ETLs. In this study, a Hf-doping strategy is proposed to enhance the transmittance of SnOx ETLs, reduce VO defects, and modulate the carrier density. The introduction of Hf dopants into SnOx successfully minimized VO-defect formation, as confirmed by Hall-effect measurements, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy, leading to a reduced carrier density in SnOx. Density functional theory simulations corroborated these experimental findings, revealing the mechanism behind VO suppression. PSCs incorporating HTO ETLs demonstrated marked improvements in key performance parameters, including short-circuit current density, VOC, and FF. Optimized HTO-based PSCs achieved an average power-conversion efficiency (PCE) of 18.23%, exhibiting a 14.2% increase compared with undoped SnOx-based devices. Additionally, the best-performing PSCs utilizing HTO ETLs achieved an optimal PCE of 21.2% under reverse scan and 19.9% under forward scan.

Optimizing Hole Transport Materials for Perovskite Solar Cells: Spiro-OMeTAD Additives, Derivatives and Substitutes

Spiro-OMeTAD (2,2',7,7'-tetrakis (N, N-di-p-methoxyphenylamine) -9,9'-spirobifluorene) has been a key hole transport material (HTM) in perovskite solar cells (PSCs) due to its excellent charge transport properties and compatibility with high-efficiency devices. However, its widespread application in PSCs is hindered by the limitations such as environmental sensitivity, high production costs, and the optimal conductivity via chemical doping process. This review explores three critical approaches to addressing these challenges: 1) the Spiro-OMeTAD-based additives and specialized treatments, including oxygen-free processes, that enhance stability and performance; 2) the development of Spiro-OMeTAD derivatives designed to improve HTM properties such as moisture resistance; 3) the exploration of Spiro-OMeTAD substitutes with cost-effectiveness and better scalability. By examining these strategies, this review provides the insights based on the traditional Spiro-OMeTAD to improve the efficiency, stability, and commercial viability of PSCs. The findings are intended to guide future research and development in the advancing PSCs technology towards broader adoption.

Enhancing the Morpho-Structural Stability of FAPbBr3 Solar Cells via 2D Nanoscale Layer Passivation of the Perovskite Interface: An In-Situ XRD Study

Despite the huge progress achieved in the optimization of perovskite solar cell (PSC) performance, stability remains a limiting factor for technological commercialization. Here, a study on the photovoltaic, structural and morphological stability of semi-transparent formamidinium lead bromide-based PSCs is presented. This work focuses on the positive role of 2D nanoscale layer passivation, induced by perovskite surface treatment with a mixture of iso-Pentylammonium chloride (ISO) and neo-Pentylammonium chloride (NEO). In situ X-ray diffraction (XRD) is applied in combination with atomic force microscopy (AFM), and the results are correlated to the devices' photovoltaic performances. The superior power conversion efficiency and overall stability of the ISO-NEO system is evidenced, as compared to the un-passivated device, under illumination in air. Furthermore, the role of the ISO-NEO treatments in increasing the morpho-structural stability is clarified as follows: a bulk effect resulting in a protective role against the loss in crystallinity of the perovskite 3D phase (observed only for the un-passivated device) and an interface effect, being the observed 2D phase crystallinity loss spatially localized at the interface with the 3D phase where a higher concentration of defects is expected. Importantly, the complete stability of the device is achieved with the passivated ISO-NEO-encapsulated device, allowing us to exclude the intrinsic degradation effects.

Steady state and transient absorption spectroscopy in metal halide perovskites

Metal halide perovskites (MHPs) have emerged as the most promising materials due to superior optoelectronic properties and great applications spanning from photovoltaics to photonics. Absorption spectroscopy provides a broad and deep insight into the carrier dynamics of MHPs, and is a critical complement to fluorescence and scattering spectroscopy. However, absorption spectroscopy is often misunderstood or underestimated, being seen as UV-vis spectroscopy only, which can lead to various misinterpretations. In fact, absorption spectroscopy is one of the most important branches of spectroscopic techniques (others including fluorescence and scattering), which plays a critical role in understanding the electronic structure and optoelectrical dynamics of MHPs. In this tutorial, the basic principles of various types of absorption spectroscopy as well as their recent developments and applications in MHP materials and devices are summarized, covering comprehensive advances in steady state and transient absorption spectroscopy. Given the significance of absorption spectroscopy in directing the design of different optoelectronic applications of MHPs, this tutorial will comprehensively discuss absorption spectroscopy, covering wavelengths from optical to terahertz (THz) and microwave, and timescales from femtoseconds to hours, and it specifically focuses on time-dependent steady-state and transient absorption spectroscopy under light illumination bias to study MHP materials and devices, allowing researchers to select suitable characterization techniques.

B-Site Mixing Effects in Hybrid Perovskites: Phase Transitions and Dielectric Response of MAPb1-x Sn x Br3

Ion-mixing is a highly effective strategy for tuning the performance and stability of photovoltaic devices based on hybrid perovskites. Despite many works concentrating on the A- and X-site mixing effects, a comprehensive study on the effects of B-site mixing on the structural and dynamic properties of MA-based perovskites is still absent. In this work, we investigate the structural and dynamic properties of mixed lead-tin halide perovskites MAPb1-x Sn x Br3 using a multitechnique experimental approach including differential scanning calorimetry, dielectric spectroscopy, and nuclear quadrupole resonance experiments. We map the phase diagram of this system, which reveals that B-site mixing slightly stabilizes the cubic phase and affects the MA cation dynamics and ordering, although the observed effects are less prominent compared with A- and X-site mixing. Our results provide insights into the complex interplay of structural and dynamic properties in mixed-metal perovskites contributing to their potential optimization for photovoltaic applications.

Reducing Nonradiative Recombination in Halide Perovskites through Appropriate Band Gaps and Heavy Atomic Masses

Halide perovskite optoelectronic devices achieve high energy conversion efficiencies. However, their efficiency decreases significantly with an increase in temperature. This decline is likely caused by changes in nonradiative recombination and electron-phonon coupling, which remain underexplored. When the perovskite lattice temperature increases, anharmonicity induces energy level fluctuation and band gap narrowing by modulating electron-phonon interactions. As lattice vibrations intensify, high-frequency phonons progressively dominate the carrier dynamic processes in halide perovskites, thereby strengthening the coupling between the electronic subsystem and high-frequency phonons. The increased overlap of electron wave functions strengthens non-adiabatic coupling, thereby accelerating the nonradiative recombination process. On the basis of these findings, we propose the introduction of appropriate band gap materials and heavy atoms at the B-site and X-site to modulate electron-phonon coupling, thereby mitigating nonradiative recombination and enhancing halide perovskite solar cell performance.

A Versatile Ionic Liquid Additive for Perovskite Solar Cells: Surface Modification, Hole Transport Layer Doping, and Green Solvent Processing

Hole-transport layers (HTL) in perovskite solar cells (PSCs) with an n-i-p structure are commonly doped by bis(trifluoromethane)sulfonimide (TFSI) salts to enhance hole conduction. While lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dopant is a widely used and effective dopant, it has significant limitations, including the need for additional solvents and additives, environmental sensitivity, unintended oxidation, and dopant migration, which can lead to lower stability of PSCs. A novel ionic liquid, 1-(2-methoxyethyl)-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (MMPyTFSI), is explored as an alternative dopant for 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamino)-9,9'-spirobifluorene (spiro-OMeTAD). MMPy ions act as a surface passivator, reducing defects on the perovskite surface, while TFSI ions facilitate p-type doping. MMPyTFSI functions as an efficient dopant, maintaining excellent performance even when tetrahydrofuran (THF) is utilized as a solvent in place of chlorobenzene (CB), while significantly reducing the environmental impact of the process. The optimized PSC achieves a power conversion efficiency (PCE) of 23.10% and demonstrates enhanced long-term stability in all aging tests for over 1000 h in a humid atmosphere, at high temperature, and under simulated sunlight illumination. These results demonstrate that MMPyTFSI is an effective and environmentally friendly dopant for producing stable and efficient PSCs.

Synergistic Hybrid-Ligand Passivation of Perovskite Quantum Dots: Suppressing Reduced-Dimensionality and Enhancing Optoelectronic Performance

In terms of surface passivation for realizing efficient CsPbI3-perovskite quantum dot (CsPbI3-PQD)-based optoelectronic devices, phenethylammonium iodide (PEAI) is widely used during the ligand exchange. However, the PEA cation, due to its large ionic radius incompatible with the 3D perovskite framework, acts as an organic spacer within polycrystalline perovskites, leading to the formation of reduced dimensional perovskites (RDPs). Despite sharing the identical 3D perovskite framework, the influence of PEAI on the structure of CsPbI3-PQDs remains unexplored. Here, it is revealed that PEAI can induce the formation of high-n RDPs (n > 2) within the CsPbI3-PQD solids, but these high-n RDPs undergo an undesirable phase transition to low-n RDPs, leading to the structural and optical degradation of CsPbI3-PQDs. To address the PEAI-induced issue, we employ triphenylphosphine oxide (TPPO) as an ancillary ligand during the ligand exchange process. The incorporation of TPPO prevents H2O penetration and regulates the rapid diffusion of PEAI, suppressing the formation of low-n RDPs. Moreover, TPPO can passivate the uncoordinated Pb2+ sites, reducing the nonradiative recombination. This hybrid-ligand exchange strategy using both PEAI and TPPO enables realizing efficient and stable CsPbI3-PQD-based light-emitting diode (external quantum efficiency of 21.8%) and solar cell (power conversion efficiency of 15.3%) devices.

Multifunctional Graphdiyne Enables Efficient Perovskite Solar Cells via Anti-Solvent Additive Engineering

Finding ways to produce dense and smooth perovskite films with negligible defects is vital for achieving high-efficiency perovskite solar cells (PSCs). Herein, we aim to enhance the quality of the perovskite films through the utilization of a multifunctional additive in the perovskite anti-solvent, a strategy referred to as anti-solvent additive engineering. Specifically, we introduce ortho-substituted-4'-(4,4″-di-tert-butyl-1,1':3',1″-terphenyl)-graphdiyne (o-TB-GDY) as an AAE additive, characterized by its sp/sp2-cohybridized and highly π-conjugated structure, into the anti-solvent. o-TB-GDY not only significantly passivates undercoordinated lead defects (through potent coordination originating from specific high π-electron conjugation), but also serves as nucleation seeds to effectively enhance the nucleation and growth of perovskite crystals. This markedly reduces defects and non-radiative recombination, thereby increasing the power conversion efficiency (PCE) to 25.62% (certified as 25.01%). Meanwhile, the PSCs exhibit largely enhanced stability, maintaining 92.6% of their initial PCEs after 500 h continuous 1-sun illumination at ~ 23 °C in a nitrogen-filled glove box.

Optimization & enhancement of KGeCl3-based perovskite solar cells through charge transport layer engineering

The growing demand for efficient, stable, and environmentally friendly photovoltaic technologies has motivated the exploration of nontoxic perovskite materials such as KGeCl3. However, the performance of KGeCl3-based perovskite solar cells (PSCs) depends heavily on the compatibility of charge transport layers (CTLs) and optimization of device parameters. In this study, six PSC configurations were simulated using SCAPS-1D software, incorporating CTLs such as Alq3, CSTO, V2O5, nPB, and Sb2S3. Key optimization steps included analyzing CTL-perovskite heterojunction compatibility, evaluating band offsets, electric potential distribution, and recombination rates, followed by fine-tuning layer thickness, doping concentration, defect density, electrode work function, and back-end reflectivity. These optimizations significantly reduced recombination losses, enhanced charge carrier extraction, and improved light absorption, leading to substantial performance improvements. The CSTO-KGeCl3-nPB configuration demonstrated the highest power conversion efficiency (PCE) of 29.30%, outperforming other optimized configurations, such as Alq3-KGeCl3-nPB and Alq3-KGeCl3-Sb2S3, which achieved PCE values of 25.19% and 24.87%, respectively. This comprehensive optimization study highlights the potential of KGeCl3 as a promising absorber material for PSCs. The findings pave the way for developing efficient, stable, and sustainable photovoltaic solutions, contributing to the advancement of clean energy technologies.

Enhanced Efficiency and Intrinsic Stability of Wide-Bandgap Perovskite Solar Cells Through Dimethylamine-Based Cation Engineering

High efficiency and stable wide-bandgap (WBG) perovskite solar cells (PSCs) are crucial for the development of perovskite-based tandem solar cells. However, the efficiency and stability of WBG PSCs are compromised by significant phase segregation and surface defects. In this study, we introduce a cation engineering strategy for WBG perovskite, employing a two-step sequential method that incorporates dimethylamine hydroiodide (DMAI) into the lead halide complex during the initial step. The addition of DMAI modifies the crystal structure and grain growth of the perovskite film, leading to improved crystal quality, reduced photo-induced halide segregation, decreased defect density, and enhanced charge carrier mobility. Consequently, we achieved a champion power conversion efficiency (PCE) of 21.9 % for 1.68 eV WBG PSCs. Furthermore, the stability of PSCs based on DMA-doped perovskite was significantly improved. After 1500 hours of exposure to ambient air, the unencapsulated device retained an impressive 80.6 % of its initial efficiency. This result highlights the substantial potential for stable and efficient WBG PSCs.

Three-Dimensional (3D) Fluoride Molecular Glue to Improve the SnO2/Perovskite Interface for Efficient Perovskite Solar Cells

Aiming at numerous defects at SnO2/perovskite interface and lattice mismatch in perovskite solar cells (PSCs), we design a kind of three-dimensional (3D) molecular glue (KBF4-TFMSA), which is derived from strong intramolecular hydrogen bonding interaction between potassium tetrafluoroborate (KBF4) and trifluoromethane-sulfonamide (TFMSA). A remarkable efficiency of 25.8 % with negligible hysteresis and a stabilized power output of 25.0 % have been achieved, in addition, 24.57 % certified efficiency of 1 cm2 device is also obtained. Further investigation reveals that this KBF4-TFMSA can interact with oxygen vacancies and under-coordinated Sn(IV) from the SnO2, in the meantime, FA+ (NH2-C=NH2 +) and K+ cations can be well fixed by hydrogen bonding interaction between FA+ and BF4 -, and electrostatic attraction between sulfonyl oxygen and K+ ions, respectively. Thereby, FAPbI3 crystal grain sizes are increased, interfacial defects are significantly reduced while carrier extraction/ transportation is facilitated, leading to better cell performance and excellent stabilities. Non-encapsulated devices can maintain 91 % of their initial efficiency under maximum-power-point (MPP) tracking while continuous illumination (~100 mW cm-2) for 1000 h, and retain 91 % of the initial efficiency after 1000 h "double 60" damp-heat stability testing (60 °C and 60 %RH (RH, relatively humidity)).

Ultrathin, Friendly Environmental, and Flexible CsPb(Cl/Br)3-Silica Composite Film for Blue-Light-Emitting Diodes

Due to intrinsic defects in blue-light-emitting perovskite materials, the charge carriers are prone to being trapped by the trap states. Therefore, the preparation of efficient blue-light-emitting perovskite materials remains a significant challenge. Herein, CsPb(Cl/Br)3 nanocrystal (NCs)@SiO2 structures were fabricated through hydrolyzing (3-aminopropyl)-triethoxysilane (APTS). SiO2 can passivate the surface trap states of NCs, suppress the nonradiative recombination pathways of NCs, and effectively stabilize the surface of NCs. CsPb(Cl/Br)3 NCs@SiO2 exhibits higher photoluminescence (PL) intensity and lifetime compared to those of the pure CsPb(Cl/Br)3 NCs. The enhancement of the exciton binding energy (Eb) leads to increased PL intensity and lifetime in CsPb(Cl/Br)3 NCs @SiO2, as demonstrated by temperature-dependent PL spectra. Subsequently, a 0.3 mm film of CsPb(Cl/Br)3 NCs@SiO2/poly(methyl methacrylate) (PMMA) was fabricated through optimizing the casting method. Due to the effective protection provided by SiO2 and PMMA, CsPb(Cl/Br)3 NCs@SiO2/PMMA film exhibits excellent thermal, water, and air stability. Moreover, the CsPb(Cl/Br)3 NCs@SiO2/PMMA film also exhibits good flexibility, maintaining the PL intensity unchanged under bending conditions. Importantly, lead can be well encapsulated in SiO2 and PMMA, effectively preventing lead from leaking into the environment. This research demonstrates the potential of a CsPb(Cl/Br)3 NCs@SiO2/PMMA film for applications in the friendly environmental field of optoelectronics, including light-emitting diodes (LEDs) and flexible displays.

Crystal growth, structural phase transitions and optical gap evolution of FAPb(Br1-xClx)3 hybrid perovskites (FA: formamidinium ion, CH(NH2)2+)

Chemically tuned organic-inorganic hybrid halide perovskites based on bromide and chloride anions CH(NH2)2Pb(Br1-xClx)3 (CH(NH2)2+: formamidinium ion, FA) have been crystallized and investigated by neutron powder diffraction (NPD), single crystal X-ray diffraction (SCXRD), scanning electron microscopy (SEM) and UV-vis spectroscopy. FAPbBr3 and FAPbCl3 experience successive phase transitions upon cooling, lowering the symmetry from cubic to orthorhombic phases; however, these transitions are not observed for the mixed halide phases, probably due to compositional disorder. The band-gap engineering brought about by the chemical doping of FAPb (Br1-xClx)3 perovskites (x = 0.0, 0.33, 0.5, 0.66 and 1.0) can be controllably tuned: the gap progressively increases with the concentration of Cl- ions from 2.17 to 2.91 eV at room temperature, presenting a nonlinear behavior. This study provides an improved understanding of the structural and optical properties of these appealing hybrid perovskites.

The Effect of Antisolvent Treatment on the Growth of 2D/3D Tin Perovskite Films for Solar Cells

Antisolvent treatment is used in the fabrication of perovskite films to control grain growth during spin coating. We study widely incorporated aromatic hydrocarbons and aprotic ethers, discussing the origin of their performance differences in 2D/3D Sn perovskite (PEA0.2FA0.8SnI3) solar cells. Among the antisolvents that we screen, diisopropyl ether yields the highest power conversion efficiency in solar cells. We use a combination of optical and structural characterization techniques to reveal that this improved performance originates from a higher concentration of 2D phase, distributed evenly throughout the 2D/3D Sn perovskite film, leading to better crystallinity. This redistribution of the 2D phase, as a result of diisopropyl ether antisolvent treatment, has the combined effect of decreasing the Sn4+ defect density and background hole density, leading to devices with improved open-circuit voltage, short-circuit current, and power conversion efficiency.

Thermally Stable Anthracene-Based 2D/3D Heterostructures for Perovskite Solar Cells

Bulky organic cations are used in perovskite solar cells as a protective barrier against moisture, oxygen, and ion diffusion. However, bulky cations can introduce thermal instabilities by reacting with the near-surface of the 3D perovskite forming low-dimensional phases, including 2D perovskites, and by diffusing away from the surface into the film. This study explores the thermal stability of Cs0.09FA0.91PbI3 3D perovskite surfaces treated with two anthracene salts─anthracen-1-ylmethylammonium iodide (AMAI) and 2-(anthracen-1-yl)ethylammonium iodide (AEAI)─and compares them with the widely used phenethylammonium iodide (PEAI). The steric hindrance of AMAI limits the interaction of its NH3+ head with the perovskite lattice, relative to what is seen with AEAI and PEAI. As a result, AMAI requires more thermal energy to convert the 3D perovskite surface to a 2D perovskite. Annealing of perovskite surfaces treated with the iodide salts results in decreased power conversion efficiencies (PCEs) for PEAI and AEAI, while a PCE enhancement is observed for AMAI. Importantly, AMAI-treated devices show enhanced stability upon annealing of the film and a 100% yield of working pixels after a high-temperature stability test at 85 °C, representing the most reliable device configuration among all those studied in this work. These results reveal the potential of AMAI as a scalable surface treatment.

Capillary Force-Assisted CsPbBr3-xIx (x = 0, 1) Columnar Crystal Film for X-ray Detectors with Ultrahigh Electric Field and Sensitivity

Inorganic halide perovskite thin-film X-ray detectors have attracted great research interest in recent years due to their high sensitivity, low detection limit, and facile fabrication process. The poor crystal quality of the thin film with uncontrollable thickness and low background voltage during detection limits its practical application. Here, a high-quality CsPbBr3-xIx (x = 0, 1) columnar crystal film is prepared by an improved melt-confined method with a porous anodic aluminum oxide (AAO) template, which stabilizes the disorder perovskite systems of CsPbBr2I by stress. The AAO-CsPbBr3-xIx (x = 0) detectors exhibit high detection accuracy and photoelectric conversion capability with an ultrahigh sensitivity of 32,399.5 μC·Gyair-1·cm-2 at 2142.9 V mm-1 under 20 kVp X-rays and 19,217.4 μC·Gyair-1·cm-2 with a higher background electric field of 6666.7 V mm-1 for AAO-CsPbBr3-xIx (x = 1). Moreover, the AAO-CsPbBr3-xIx (x = 1) film detector acquires a lower detection limit of 7.65 nGy·s-1 and a higher X-ray imaging spatial resolution of 1.6 LP/mm and 8.6 nGy·s-1 and 1.4 LP/mm for AAO-CsPbBr3-xIx (x = 0). The facile, high-quality columnar crystal film devices display great potential for low-energy and low-dose X-ray imaging in flat panel detection applications.

Ligand-Mediated Surface Reaction for Achieving Pure 2D Phase Passivation in High-Efficiency Perovskite Solar Cells

The surface passivation with the heterostructure of the 2D/3D stack has been widely used for boosting the efficiency of n-i-p perovskite solar cells (PSCs). However, the disordered quantum well width distribution of 2D perovskites leads to energy landscape inhomogeneity and crystalline instability, which limits the further development of n-i-p PSCs. Here, a versatile approach, ligand-mediated surface passivation, was developed to produce a phase-pure 2D perovskite passivation layer with a homogeneous energy landscape by dual-ligand codeposition. The preferential adsorption of 3,6-dimethyl-carbazole-9-ethylammonium iodide with a large molecular size and lower adsorption energy could regulate the surface reaction between the m-fluorophenylethylammonium iodide and perovskite surface, resulting in a 2D perovskite with a narrow quantum well distribution and a uniform surface potential distribution. Beyond this, the preservation of the surface-confined 2D passivation layer retained a higher electric field at the interface of perovskite and the hole transport layer. As a result, the champion device reached an efficiency of 25.86% for the 0.05 cm2 device and 25.08% for the 1 cm2 device, with enhanced operational stability (T90 > 1000 h) and much better thermal stability. Our work provides deeper insights into efficient and stable 2D passivation for PSCs.

Boosting Stability of Cesium/Formamidinium Based Perovskite Solar Cells via Eliminating Intermediate Phase Transition and X-Anion Vacancy

Boosting the stability of cesium/formamidinium (Cs/FA) based perovskite solar cells (PSCs) has received tremendous attention. However, the crystallization of perovskites usually undergoes complex intermediate phase transitions and ion loss processes, which seriously degrade the efficiency and stability of PSCs. Herein, iodine monobromide (IBr, an interhalogen) is incorporated into the precursor solution to regulate the perovskite crystallization process. IBr can directly induce the formation of perovskite crystal nuclei in the intermediate film, avoiding a complex phase transformation (2H-4H-3C). This leads to a reduction in the impurity phase, an increase in grain size, and an improvement in crystal quality. Furthermore, IBr can effectively compensate X-anion vacancy, thereby reducing defect density and nonradiative recombination, which enhances device performance. Thus, the efficiency of the optimal device is 24.82%. Simultaneously, the device demonstrated excellent stability. After 400 h of continuous operation, the efficiency value of the unencapsulated PSCs still retains 89% of its initial value. This study provides an effective strategy for manufacturing PSCs with excellent efficiency and stability.

Synthesis of Multifunctional Organic Molecules via Michael Addition Reaction to Manage Perovskite Crystallization and Defect

Additive engineering plays a pivotal role in achieving high-quality light-absorbing layers for high-performance and stable perovskite solar cells (PSCs). Various functional groups within the additives exert distinct regulatory effects on the perovskite layer. However, few additive molecules can synergistically fulfill the dual functions of regulating crystallization and passivating defects. Here, we custom-synthesized 2-ureido-4-pyrimidone (UPy) organic small molecules with diverse functional groups as additives to modulate crystallization and defects in perovskite films via the Michael addition reaction. Theoretical and experimental investigations demonstrate that the -OH groups in UPy exhibit significant effects in fixing uncoordinated Pb2+ ions, passivation of lead-iodide antisite defects, alleviating hysteresis, and reducing non-radiative recombination. Furthermore, the enhanced C=O and -NH2 motifs interact with the A-site cation via hydrogen bonding, which relieves residual strain and adjusts crystal orientation. This strategy effectively controls perovskite crystallization and passivates defects, ultimately enhancing the quality of perovskite films. Consequently, the open-circuit voltage of the UPy-based p-i-n PSCs reaches 1.20 V, and the fill factor surpasses 84 %. The champion device delivers a power conversion efficiency of 25.75 %. Remarkably, the unencapsulated device maintained 96.9 % and 94.5 % of its initial efficiency following 3,360 hours of dark storage and 1,866 hours of 1-sun illumination, respectively.

Visible Light-Triggered Self-Welding Perovskite Solar Cells and Modules

Flexible perovskite solar cells (F-PSCs) are highly promising for both stationary and mobile applications because of their advantageous features, including mechanical flexibility, their lightweight and thin nature, and cost-effectiveness. However, a number of drawbacks, such as mechanical instability, make their practical application difficult. Here, self-welding dynamic diselenide that is triggered by visible light into the structure of F-PSCs to improve their long-term stability by repairing cracks and defects in the absorber layer is incorporated. The diselenide confers the flexibility and self-welding properties to the Cs0.05MA0.05FA0.9PbI3 perovskite layer, enabling optimized F-PSC devices to achieve a power conversion efficiency of 24.85% while retaining ca. 92% of their initial efficiency after undergoing 15 000 bending cycles at a curvature radius of 3 mm. The corresponding flexible large-scale module with an active area of 15.82 cm2 achieved a record PCE of 21.65%.

Dual Crystal-Liquid Thermal Transport Behavior in MAPbCl3

Phonon dynamics in organic-inorganic hybrid perovskites (OIHPs) exhibit inherent complexity driven by the intricate interactions between rotatable organic cations and dynamically disordered inorganic octahedra, mediated by hydrogen bonding. This study aims to address this complexity by investigating the thermal transport behavior of MAPbCl3 as a gateway to the OIHPs family. The results reveal that the ultralow thermal conductivity of MAPbCl3 arises from a synergistic interplay of exceptionally low phonon velocities, short phonon lifetimes, and phonon mean free paths approaching the Regel-Ioffe limit. Additionally, the thermal conductivity of MAPbCl3 approaches its theoretical amorphous limit across a broad temperature range, with its thermal transport behavior transitioning from crystal-like to more liquid-like during the orthorhombic-to-cubic phase transitions. Furthermore, a phonon drag effect is observed at 17 K, with Umklapp scattering serving as the predominant phonon resistive mechanism in the orthorhombic phase. In contrast, dynamic lattice distortions caused by the jumping rotation of MA+ cations become the primary factors influencing thermal transport in the cubic phase.

Advances in Self-Healing Perovskite Solar Cells Enabled by Dynamic Polymer Bonds

This comprehensive review addresses the self-healing phenomenon in perovskite solar cells (PSCs), emphasizing the reversible reactions of dynamic bonds as the pivotal mechanism. The crucial role of polymers in both enhancing the inherent properties of perovskite and inducing self-healing phenomena in grain boundaries of perovskite films are exhibited. The review initiates with an exploration of the various stability problems that PSCs encounter, underscoring the imperative to develop PSCs with extended lifespans capable of self-heal following damage from moisture and mechanical stress. Owing to the strong compatibility brought by polymer characteristics, many additive strategies can be employed in self-healing PSCs through artful molecular design. These strategies aim to limit ion migration, prevent moisture ingress, alleviate mechanical stress, and enhance charge carrier transport. By scrutinizing the conditions, efficiency, and types of self-healing behavior, the review encapsulates the principles of dynamic bonds in the polymers of self-healing PSCs. The meticulously designed polymers not only improve the lifespan of PSCs through the action of dynamic bonds but also enhance their environmental stability through functional groups. In addition, an outlook on self-healing PSCs is provided, offering strategic guidance for future research directions in this specialized area.

Implementing Lattice and Energy Level Matching to Optimize Buried Interfaces for High-Performance Perovskite Solar Cells

In n-i-p type perovskite solar cells (PSCs), mismatches in energy level and lattice at the buried interface is highly detrimental to device performance. Here, thin PbS interconnect layer in situ coating on the SnO2 surface is grown. The function of PbS at the interface is different from the commonly used function of crystalline seeds in perovskite bulk. The theoretical calculation show that it helps construct an interconnect structure of SnO2/PbS/Perovskite with matched energy level and lattice. This not only increases conductivity of SnO2, but also upshifts Fermi energy levels (EF) of both SnO2 and buried perovskite due to charge transfer and perovskite's internal defect changes. Such a suitable energy level arrangement ensures a better energy level match at the interface, favoring efficient charge transfer and less open circuit voltage (Voc) loss. Additionally, in situ PL reveals that the template effect of PbS enable perovskite grain to grow bottom-up because of their highly matched lattice parameters. This growth mode optimizes buried interface contact and crystallinity of perovskite. Ultimately, after PbS modification, a remarkable power conversion efficiency (PCE) exceeding 24% and better device stability are obtained. This work demonstrates an effective interconnect layers strategy to realize ideal interface contact toward high-performance PSCs.

A Stepwise Melting-Polymerizing Molecule for Hydrophobic Grain-Scale Encapsulated Perovskite Solar Cell

Despite the ongoing increase in the efficiency of perovskite solar cells, the stability issues of perovskite have been a significant hindrance to its commercialization. In response to this challenge, a stepwise melting-polymerizing molecule (SMPM) is designed as an additive into FAPbI3 perovskite. SMPM undergoes a three-stage phase transition during the perovskite annealing process: initially melting from solid to liquid state, followed by overflowing grain boundaries, and finally self-polymerizing to form a hydrophobic grain-scale encapsulation in perovskite solar cells, providing protection against humidity-induced degradation. With this unique property, coupled with the advantages of improved crystallization, diminished non-radiative recombination, and energy level alignment, FAPbI3-based perovskite solar cells with a 25.21% (small-area) and 22.94% (1 cm2) power conversion efficiency and over 2000 h T95% stability under 85% relative humidity is achieved. Furthermore, the SMPM-based perovskite solar cells without external encapsulations sustain impressive stability during underwater operation, in which the black FAPbI3 phase is maintained and Pb-leakage is also effectively suppressed. Therefore, the SMPM strategy can offer a sustainable settlement in both stability and environmental issues for the commercialization of perovskite solar cells.

Multifunctional Regulation of Chemical Bath Deposition Based SnO2 for Efficient Perovskite Solar Cells

SnO2 prepared by chemical bath deposition (CBD) is among the most promising electron transport layers for enabling high efficiency, large area perovskite solar cells (PSCs). However, the uneven surface coverage of SnO2 and the presence of defects in the film and/or at the SnO2/perovskite interface significantly affect the device performance. Herein, a multifunctional molecule of phosphorylcholine chloride (CP) is introduced to modulate the CBD growth of SnO2 and suppress the generation of defects. The agglomeration of SnO2 nanoparticles is hindered due to the electrostatic repulsion effect, leading to the formation of dense and conformal films with improved optical transmittance and electrical conductivity. Moreover, the defects both in SnO2 and at the interface of SnO2/perovskite are successfully passivated and the energy band structure is well regulated, contributing to the suppression of nonradiative recombination and the improvement of electron transport. As a result, a remarkably high power conversion efficiency (PCE) of 24.04% is attained for PSCs processed in air ambient. The unencapsulated devices exhibit improved long-term stability, maintaining over 80% of their initial PCE after storing in air ambient for 1500 h or under one-sun illumination for 600 h.

Thiol Groups Reutilization on Chemical Bath Deposited Tin Oxide Surface Achieving Interface Anchoring and Defects Passivation for Enhancing the Performance and Stability of Perovskite Solar Cells

Due to its simple process and adaptability to large-area deposition, chemical bath deposition (CBD) is one of the preparation methods for the SnO2 layer in highly efficient "n-i-p" structured perovskite solar cells (PSCs). However, the residual thioglycolic acid (TGA) on the CBD-SnO2 surface affects the stability of PSCs and the carrier transport at the CBD-SnO2/perovskite interface, hindering the further development of this method. This work demonstrates a method for the reutilization of surface groups to construct molecular bridges. This strategy utilizes the substitution reaction between the residual thiol group on the CBD-SnO2 surface and the iodine group of iodoacetamide (IAM) to form the IAM structure. The IAM structure not only assists the perovskite grain crystallization but also increases the electronic cloud density of the CBD-SnO2 surface. Consequently, the charge mobility of the CBD-SnO2 is enhanced and the energy band alignment at the CBD-SnO2/perovskite interface is optimized. A champion device with the IAM structure achieved a power conversion efficiency (PCE) of 22.41% while it maintained 80% of its original PCE after placing at 65 °C in nitrogen filled atmosphere for over 300 h and in an environment at 25 °C and 50 ± 5% relative humidity for over 1000 h, respectively.