Homogenized NiOx nanoparticles for improved hole transport in inverted perovskite solar cells

Fluid Chemistry of Metal Halide Perovskites

Solution-processed metal halide perovskites (MHPs) have been rapidly developed worldwide, with much attention to fluid dynamic, fluid crystallization, and fluid interfaces, all falling within the realm of fluid chemistry. It is widely recognized that the theory of fluid chemistry has been proven to provide an effective means for the improvement of perovskite crystallization and the enhancement of perovskite solar cells (PSCs) performance. In this review, the fluid behavior, microfluidic synthesis, and aging process of perovskite materials are first investigated, with emphasis on the related improvement methods and chemical mechanisms. Second, the internal crystallization chemistry, external interface chemistry, and the large-area PSCs based on the fluid chemistry are discussed. Finally, four specific directions for future studies of fluid chemistry of MHPs are proposed, aiming to harness the theoretical advantages of fluid chemistry and contribute to the industrialization of PSCs.

Efficient perovskite solar modules enabled by a UV-stable and high-conductivity hole transport material

Ultraviolet (UV) radiation poses a substantial challenge to the stability of prevalent p-i-n (positive-intrinsic-negative) perovskite solar cells (PSCs), demanding more robust hole-transport layers (HTLs) due to light incident from the HTL side. Here, we unveil that commonly used self-assembled monolayer (SAM)-type HTLs suffer from poor UV stability that causes irreversible damage to hole extraction and impairs device stability. To address this issue, we develop a polymeric and UV-stable HTL named Poly-2PACz, which exhibits strong binding to substrates and exceptional UV resistance over SAM-type HTLs. The PSCs blade-coated under ambient conditions using Poly-2PACz HTL achieved a remarkable efficiency of 26.0% and outstanding UV stability. Our cells retain 80% of the initial PCE even after about 500 hours of high-intensity UV illumination [7.7 times higher than that of air mass 1.5 global (AM 1.5G) solar spectrum]. Furthermore, Poly-2PACz exhibits good wettability and high conductance, enabling the fabrication of blade-coated minimodules with an aperture efficiency of 22.2% and excellent uniformity.

Modification at ITO/NiOx Interface with MoS2 Enables Hole Transport for Efficient and Stable Inverted Perovskite Solar Cells

Inverted perovskite solar cells (IPSCs) utilizing nickel oxide (NiOx) as hole transport material have made great progress, driven by improvements in materials and interface engineering. However, challenges remain due to the low intrinsic conductivity of NiOx and inefficient hole transport. In this study, we introduced MoS2 nanoparticles at the indium tin oxide (ITO) /NiOx interface to enhance the ITO surface and optimize the deposition of NiOx, resulting in increased conductivity linked to a ratio of Ni3+:Ni2+. This interface modification not only optimized energy level but also promoted hole transport and reduced defects. Consequently, IPSCs with MoS2 modified at ITO/NiOx interface achieved a champion power conversion efficiency (PCE) of 21.42 %, compared to 20.25 % without modification. Additionally, unencapsulated IPSCs with this interface modification displayed improved stability under thermal, light, humidity and ambient conditions. This innovative strategy for ITO/NiOx interface modification efficiently promotes hole transportation and can be integrated with other interface engineering approaches, offering valuable insights for the development of highly efficient and stable IPSCs.

3D Patterning of Perovskite Quantum Dots via Direct In Situ Femtosecond Laser Writing

Perovskite quantum dots (PQDs) exhibit remarkable optical properties, making them highly promising for next-generation display technologies. However, achieving precise PQDs patterning is hindered by significant challenges, including the inability to achieve true three-dimensional (3D) structuring and the risk of damaging the delicate perovskite crystal lattice. Existing methods struggle to achieve true 3D structuring while preserving the optical integrity. This study introduces an in situ patterning technique using direct laser writing (DLW). By leveraging the nonlinear absorption properties of femtosecond lasers, thiol-Ene photopolymerization is triggered, transforming perovskite precursors into complex fluorescent structures. Unlike conventional methods, this precursor-based approach minimizes laser power requirements and prevents quantum dot degradation caused by high-energy exposure. It enables precise, scalable fabrication while maintaining the structural and optical stabilities of PQDs. This innovation provides a robust platform for developing advanced display technologies, optoelectronic devices, and miniaturized on-chip systems, paving the way for future high-performance applications.

Reconstruction of the Buried Interface of Triple-Halide Wide-Bandgap Perovskite for All-Perovskite Tandems

All-perovskite tandem solar cells (TSCs) paired by wide-bandgap (WBG) perovskites with narrow-bandgap perovskites holds the potential to overcome the Shockley-Queisser limitation. However, the severe phase segregation and non-radiative recombination of WBG perovskite put on a shadow for their power conversion efficiency and stability. Here, an interfacial engineering strategy is introduced into the triple-halide WBG perovskite. Potassium trifluoromethanesulfonate (TfOK) is utilized to reconstruct the buried interface of the triple-halide WBG perovskite. The distribution of (chlorine) Cl- changes from perovskite bulk toward the buried interface due to the TfOK addition. Therefore, a wider bandgap perovskite thin layer is formed at buried layer, which can form a graded heterojunction with bulk WBG perovskite to improve carrier separation and transfer. Meanwhile, the (potassium) K+ of TfOK diffuses into WBG perovskite bulk to suppress halide phase segregation. Consequently, the 1.78 eV WBG PSCs deliver an impressive power conversion efficiency of 20.47% and an extremely high fill factor over 85%. Furthermore, the resultant two-terminal all-perovskite TSCs achieves a champion efficiency of 28.30%. This strategy provides a unique avenue to improve performance and photostability of WBG PSCs, a new function of Cl- in triple-halide is illustrated.

Simple I-Shaped Aryl-Based Dyes for Tin Perovskite Solar Cells with Selenophene Core Moiety as Self-Assembled Monolayers on NiOx Using Two-Step Fabrication

Six novel organic small molecules, TPA-Sp-PA (1), TPA-Sp-PE (1E), TPA-T-PA (2), TPA-T-PE (2E), TPA-P-PA (3) and TPA-P-PE (3E) are developed and applied to NiOx films as self-assembled monolayers (SAMs) for tin perovskite solar cells (TPSCs). The linker between acceptor (phosphonic acid (PA) or phosphonic ester (PE)) and donor (triphenylamine (TPA)) plays an important role in facilitating the growth of high-quality perovskite films using a two-step method. Three different types of linkers, phenyl ring (P), thiophene (T), and selenophene (Sp), are studied, for which the Sp-based SAMs provide the best device performance with TPA-Sp-PE (1E) achieving a PCE 8.7%, and its acidic analog, TPA-Sp-PA (1), reaching a maximum PCE of 8.3%. Single crystal structures of TPA-Sp-PE (1E) and TPA-T-PE (2E) are successfully obtained, with the expectation that a uniform SAM would form on the NiOx/ITO substrate. The research introduces a novel approach to enhance TPSC performance by integrating organic SAMs with NiOx HTMs, offering a promising avenue for future progress in TPSC technology through a two-step fabrication technique.

Colloidal Self-Assembly of CuCrO2 Nanocrystals for Durable Inverted Perovskite Solar Cells

Despite the promise of self-assembled organic hole-transport layers (HTLs) in inverted perovskite solar cells, critical concerns persist about their structural stability under external fields such as bias and illumination, which have been regarded as a potential threat to the device's longevity. To address this issue, instead of using self-assembled organic molecules, the intrinsically stable p-type, wide bandgap CuCrO2 colloidal nanocrystals with high monodispersity are synthesized and self-assembled them into HTL via a simple dip-coating method. By further HCl-mediated ligands exchange, the self-assembled CuCrO2-HTL creates a thermally stable chlorinated surface that can not only enhance the electronic coupling of inter nanocrystals but also provide contact passivation on the perovskite surface defects. These merits eventually endow the constructed buried interface with favorable contact, thus facilitating efficient and stable hole transfer. Consequently, an impressive power conversion efficiency of 25.35% is achieved, accompanied by greatly improved longevity under different accelerated-aging tests.

Double Hole Transport Layers Enable 20.42% Efficiency Organic Solar Cells by Aggregation Control of Self-Assembled Molecules on Cobalt Salt Surfaces

Heterojunction interfaces play a crucial role in charge carrier transport, influencing the overall photovoltaic performance of organic solar cells (OSCs). Despite the importance, advancements in interfacial engineering, especially in optimizing the microstructure and nanomorphology, have not kept pace with research on photoactive layers. In the study, a strategy is explored to control the self-assembly growth of alcohol-soluble Me-4PACz (4P) used as a hole transport layer (HTL) in OSCs. The surface architecture is modified of inorganic Co salts via Cu doping and UV-ozone treatments, creating a smooth top surface with an increased Co3+/Co2+ ratio and hydroxyl groups. This meticulous design fine-tuned the assembly behavior of self-assembled molecules, resulting in the transition from spherical aggregates to a more uniform worm-like morphology. Additionally, the electrical and optical properties are optimized to passivate surface defects and enhance the wettability of organic solvents, leading to improved hole extraction and reduced interfacial charge carrier recombination losses. Consequently, an OSC with Cu-Co/4P as the HTL exhibited the highest power conversion efficiency of 20.42% (certified 20.20%). The characteristic universality and stability make the Cu-Co/4P HTL a potential candidate for widespread applications, particularly in providing rationalized guidance to further enhance the performance of OSCs.

Charge Polarization Tunable Interfaces for Perovskite Solar Cells and Modules

Interfacial localized charges and interfacial losses from incompatible underlayers are critical factors limiting the efficiency improvement and market-integration of perovskite solar cells (PSCs). Herein, a novel interfacial chemical tuning strategy is proposed involving proton transfer between the amine head of pyridoxamine (PM) and the phosphonic acid anchoring group of [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz), with simultaneous enhancement of charge delocalization through electrostatic attraction between opposite charged molecules. The Me-4PACz-PM charge polarization interface modulates the nickel oxide (NiOx) charge states and the coordination environment at buried interfaces, consequently enhancing p-type conductivity and obtaining a more compatible band arrangement. The high-coverage and wettability of the NiOx/Me-4PACz-PM underlayer also facilitate the deposition of high-quality perovskite films, releasing lattice strain and mitigating trap-assisted non-radiative recombination. Attributing to the implementation of charge polarization tunable interfaces, small-area devices and modules with an aperture area of 69 cm2 achieved impressive power conversion efficiencies (PCEs) of 26.34% (certified 25.48%) and 21.94% (certified 20.50%), respectively, and unencapsulated devices maintained their initial PCEs ≈90% after aging for 2000 h (ISOS-L-1) and 1500 h (ISOS-D-1). The broad applicability of charge polarization tunable interfaces and the successful scaling of large-area modules provide a reference for expanding PSCs applications.

Advancing Self-Assembled Molecules Toward Interface-Optimized Perovskite Solar Cells: from One to Two

Perovskite solar cells (PSCs) have rapidly gained prominence as a leading candidate in the realm of solution-processable third-generation photovoltaic (PV) technologies. In the high-efficiency inverted PSCs, self-assembled monolayers (SAMs) are often used as hole-selective layers (HSLs) due to the advantages of high transmittance, energy level matching, low non-radiative recombination loss, and tunable surface properties. However, SAMs have been recognized to suffer from some shortcomings, such as incomplete coverage, weak bonding with substrate or perovskite, instability, and so on. The combination of different SAMs or so-called co-SAM is an effective strategy to overcome this challenge. In this Perspective, the latest achievements in molecule design, deposition method, working principle, and application of the co-SAM are discussed. This comprehensive overview of milestones in this rapidly advancing research field, coupled with an in-depth analysis of the improved interface properties using the co-SAM approach, aims to offer valuable insights into the key design principles. Furthermore, the lessons learned will guide the future development of SAM-based HSLs in perovskite-based optoelectronic devices.

Anion-Cation Synergistic Regulation of Low-Dimensional Perovskite Passivation Layer for Perovskite Solar Cells

Mixing 2D and 3D perovskite together is an effective strategy to enhance the stability of perovskite solar cells (PSCs). This strategy has been widely used in many recent works. Typically, 2D layer is formed by introducing 2D spacer onto 3D surfaces through in situ intercalation reaction. However, this intercalation may not stop after the 2D layer is formed. Progressive migration of 2D spacer into 3D bulk leads to increased n-values of 2D phases and deviation from optimized structural design. The high n-value 2D perovskite is less stable than the low n-value 2D perovskite and may be prone to degradation under external stresses. Here, a heteroatom ammonium ligand, thiomorpholine (SMOR) is found, which can effectively passivate the perovskite surface, and form a 1D phase or 2D phase depending on cation to anion ratio and the type of anions. Due to lower formation energy at 1:1 cation to anion ratio, 1D phase can prevent the formation of high-n-value 2D phase and show excellent thermal stability. The passivation of SMOR-based 1D perovskite boosts the device efficiency to 25.6% (certified 24.7%). More importantly, the unpackaged device can maintain >80% of its initial efficiency after stable operation at 85 °C for 1000 h.

Scalable Impregnation Method for Preparing a Self-Assembled Monolayer in High-Performance Vapor-Deposited Lead-Halide Perovskite Solar Cells

The power conversion efficiency (PCE) of inverted lead-halide perovskite solar cells (PSCs) via vapor deposition has undergone significant enhancement through the incorporation of a self-assembled monolayer (SAM) serving as the hole transport layer. To achieve high-performance PSCs, the SAM layer needs to maintain a dense and high-coverage configuration during the fabrication process. Our investigation revealed that during solid-vapor reaction, conditions of high temperature and low pressure can potentially lead to the migration of SAM molecules, particularly those adsorbed on the surface but have not yet formed covalent bonds. In this study, to overcome this limitation, we have developed an impregnation process for mixed SAM molecules with (4-(7H-dibenzo[c,g]carbazol-7-yl)butyl)phosphonic acid (4PADCB) and glycine hydrochloride (GH), which reduces the agglomeration of SAM molecules and enhances their strong anchoring ability with the substrate, thereby maintaining an extremely high coverage rate even in the high-temperature and low-pressure environment of solid-vapor reactions. Consequently, champion efficiencies of 22.15% (0.16 cm2) and 19.18% (5 cm × 5 cm module) are achieved, which is the highest record for inverted PSCs based on vapor deposition. Moreover, the impregnation process of the SAM layer has the advantages of reusability, good uniformity, and low cost, which has very broad commercial prospects.

Optimizing Molecular Packing and Interfacial Contact via Halogenated N-Glycidyl Carbazole Small Molecules for Low Energy Loss and Highly Efficient Inverted Perovskite Solar Cells

Nonideal interfacial contact and non-radiative voltage loss in self-assembled monolayers (SAMs)-based inverted perovskite solar cells (PSCs) limit their further development. Herein, two carbazole-based molecules with different halogen atoms (X-OCZ, X = Cl or Br) are developed as efficient interfacial regulators. The halogen effect not only finely modulates the molecular packing, crystallinity, and surface contact potential of the MeO-2PACz analogue via self-induced intermolecular interactions but also significantly influences the subsequent crystal growth of perovskite, thus resulting in the formation of high-quality films with enhanced crystallinity, improved energy level alignment, and depressed non-radiative recombination. Importantly, the Cl-OCZ-mediated device exhibits a minimal interfacial carrier transport energy barrier of 0.10 eV and an impressive charge collection efficiency of 93.6%. Moreover, the target device (aperture area: 0.09 cm2) shows an exceptional efficiency of 26.57% (certified 26.4%) along with enhanced thermal and operational stability. The strategy is also extended to large area devices, delivering efficiencies of 25.0% for a 1 cm2 device and 22.9% for a 12.96 cm2 minimodule. This study highlights the halogen role of interfacial small molecules in optimizing molecular packing and interfacial contact toward highly efficient PSCs with minimized energy loss and non-radiative recombination.

Multifunctional Hole Transport Strategy for Highly Efficient and Stable Inverted Perovskite Solar Cells

Self-assembled monolayer (SAM)-based inverted perovskite solar cells (PSCs) have exhibited excellent performance in efficiency, while the stability and reproducibility of the PSCs still need to be improved. In this work, we present a multifunctional hole transport approach for inverted PSCs, where NiOX, SAM ((E)-3-(4-(bis(4-methoxyphenyl)amino)phenyl)acrylic acid, abbreviated as MPTCA) and a wetting agent (2-phenylethylamine hydroiodide, known as PEAI) are employed for hole-transport materials (HTMs). This NiOX/MPTCA/PEAI composite layer is uniform and has good wetting properties, which enables the formation of a high-quality perovskite film, effectively minimizing defects that typically occur at the buried interface. An outstanding champion efficiency of 24.74% was obtained for the devices, followed by enhanced reproducibility with an average power conversion efficiency (PCE) of 24.13 ± 0.26%, which is notably higher than that (22.73 ± 0.62%) of the pristine MPTCA-based PSCs. More importantly, the composited HTL-based devices without encapsulation demonstrated remarkable stability, with a decrease of less than 10% in the initial efficiency after 500 h of continuous light soaking.

Function Nickel Oxide for Perovskite LEDs: Energy Level Modulation and Hole Injection Optimization

Optimizing the architecture of perovskite light-emitting diodes (PeLEDs), such as incorporating inorganic hole transporting layers (HTLs), is crucial for enhancing their operational stability. Nickel oxide (NiOx) offers a unique combination of intrinsic stability, good electron-blocking properties, excellent solution processability, and tunable optoelectronic properties, making it an ideal inorganic HTL. Understanding the basic properties of NiOx, and customizing its energy level help address the limitations in hole injection, enabling more efficient and stable display devices. This review begins with an overview of the band structure and surface chemistry of NiOx, focusing on the structure-activity relationship between NiOx and its semiconductor properties. In the following section, the synthetic chemistry of solution-process NiOx is addressed. The emphasis is placed on the possible correlation between the morphology of NiOx and its energy level. Next, strategies for tuning the energy level of NiOx are summarized. Finally, a brief prospect on NiOx-based PeLEDs is provided. It is hoped this review provides a new viewpoint for more stable and efficient PeLEDs.

Cost Effectivities Analysis of Perovskite Solar Cells: Will it Outperform Crystalline Silicon Ones?

The commercialization of perovskite solar cells (PSCs) has garnered worldwide attention and many efforts were devoted on the improvement of efficiency and stability. Here, we estimated the cost effectivities of PSCs based on the current industrial condition. Through the analysis of current process, the manufacturing cost and the levelized cost of electricity (LCOE) of PSCs is estimated as 0.57 $ W-1 and 18-22 US cents (kWh)-1, respectively, and we demonstrate the materials cost shares 70% of the total cost. Sensitivity analysis indicates that the improvement of efficiency, yield and decrease in materials cost significantly reduce the cost of the modules. Analysis of the module cost and LCOE indicates that the PSCs have the potential to outperform the silicon solar cells in the condition of over 25% efficiency and 25-year lifetime in future. To achieve this target, it is essential to further refine the fabrication processes of each layer in the module, develop stable inorganic transport materials, and precisely control material formation and processing at the microscale and nanoscale to enhance charge transport.

Robust Fully Screen-Printed Perovskite Solar Cells Based on Synergistic Ostwald Ripening

Fully screen-printed process for low-cost manufacturing significantly enhances the commercial competitiveness of perovskite solar cells (PSCs). However, the controllable crystallization in screen-printed perovskite thin films using high-viscosity ionic liquids has been suggested to be difficult, which hampers further development of fully screen-printed perovskite devices in terms of application expansion and performance improvement. Here, we report a synergistic ripening strategy to fully control crystallization by employing methylamine propionate (MAPa) ionic liquid and water (H2O, moisture in the air). We found that a reversible and sustainable ripening process was activated by integrating MAPa/H2O in both externally and internally into perovskite crystals. MAPa effectively prevents the loss of organic salts and maintains the dispersion of Pb-I framework, preventing the perovskite component loss and decomposition. H2O and organic salts trends to form hydration complexes, which lowers the energy barrier and enhances the reactivity of the humidity-induced Ostwald ripening reaction. These improvements allow the screen-printed perovskite thin films achieve controlled secondary growth and ion exchange, thereby reducing defects and optimizing energy level alignment. The resulting fully screen-printed PSCs exhibits a record power conversion efficiency of 19.47 % and an operational stability over 1,000 h with maintaining 91.6 % of the highest efficiency under continuous light stress at maximum power point.

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.

Regulating three-layer full carbon electrodes to enhance the cell performance of CsPbI3 perovskite solar cells

Carbon-based perovskite solar cells exhibit a promising application prospect due to its cost effective and attractive hydrophobic nature and chemical inertness, but are still limited to unsatisfied device efficiency. Herein, we design a triple-layer full-carbon electrode for n-i-p typed perovskite solar cells, which is comprised of a modified macroporous carbon layer, a highly conductive graphite layer and a thin dense carbon layer, and each layer undertakes different contribution to improving the cell performance. Based on this full-carbon electrode, inorganic CsPbI3 perovskite solar cells exhibit >19% certified efficiency which is the highest result among carbon-based CsPbI3 devices. On one hand, carbon quantum dots decorated on the macro-porous carbon layer can realize better energy alignment of full-carbon electrode/spiro-OMeTAD/CsPbI3 interface, on the other hand, highly conductive graphite layer is advantageous to carrier transporting. Typically, the top dense carbon layer exhibits significant thermal radiation ability, which can reduce the operational temperature of devices by about 10 °C, both from theoretical simulation and experimental testing. Thereby, packaged full-carbon electrode based CsPbI3 cells exhibit much better photothermal stability at ~70°C accompanied by white light emitting diode illumination, which exhibit no efficiency degradation after 2000 h continuous operational tracking.

Molecular contacts with an orthogonal π-skeleton induce amorphization to enhance perovskite solar cell performance

Perovskite solar cells represent a promising class of photovoltaics that have achieved exceptional levels of performance within a short time. Such high efficiencies often depend on the use of molecule-based selective contacts that form highly ordered molecular assemblies. Although this high degree of ordering usually benefits charge-carrier transport, it is disrupted by structure deformation and phase transformation when subjected to external stresses, which limits the long-term operational stability of perovskite solar cells. Here we demonstrate a molecular contact with an orthogonal π-skeleton that shows better resilience to external stimuli than commonly used conjugated cores. This molecular design yields a disordered, amorphous structure that is not only highly stable but also demonstrates exceptional charge selectivity and transport capability. The perovskite solar cells fabricated with this orthogonal π-skeleton molecule exhibited enhanced long-term durability in accelerated-ageing tests. This orthogonal π-skeleton functionality opens new opportunities in molecular design for applications in organic electronics.

Nonvolatile and Strongly Coordinating Solvent Enables Blade-coating of Efficient FACs-based Perovskite Solar Cells

Blade-coating has emerges as a critical route for scalable manufacturing of perovskite solar cells. However, the N2 knife-assisted blade-coating process under ambient conditions typically yields inferior-quality perovskite films due to inadequate nucleation control and disorderly rapid crystallization. To address this challenge, a novel solvent engineering strategy is developed through the substitution of N-methyl-2-pyrrolidone (NMP) with 1,3-dimethyl-1,3-diazinan-2-one (DMPU). The unique physicochemical properties of DMPU, characterized by low vapor pressure, strong coordination capability, and limited PbI2 solubility, synergistically regulate nucleation and crystallization kinetics. This enables rapid nucleation, stabilization of intermediate phases in wet films, and controlled crystal growth, ultimately producing phase-pure perovskite films with reduced defect density. Moreover, the feasibility and superiority of the mixed solvent strategy are demonstrated. The optimized blade-coated PSCs achieve a power conversion efficiency of 21.74% with enhanced operational stability, retaining 84% initial efficiency under continuous 1-sun illumination for 1,000 h. This work provides new insights into solvent design for preparing blade-coated perovskite films.

ALD-Deposited Hydroxyl-Rich NiOx to Enhance SAM Anchoring for Stable and Efficient Perovskite Solar Cells

The interface between nickel oxide (NiOx) and self-assembled monolayers (SAMs) in perovskite solar cells (PSCs) often suffers from limited adsorption strength, poor energy-level alignment, and inadequate defect passivation, which hinder device performance and stability. To address these issues, we introduce a hybrid hole selective layer (HSL) combining atomic layer deposition (ALD)-fabricated NiOx with full-aromatic SAM molecules, creating a highly stable and efficient interface. ALD NiOx, enriched with hydroxyl groups, provides robust adsorption sites for the SAM molecule MeO-PhPACz, ensuring a strong, stable interaction. This hybrid HSL enhances energy-level alignment, hole selectivity, and defect passivation at the NiOx/perovskite interface. Devices utilizing this approach demonstrate significant performance improvements, achieving a power conversion efficiency (PCE) of 21.74%, with reduced voltage losses and minimal hysteresis. Furthermore, operational stability tests reveal enhanced durability under elevated humidity and temperature conditions. These findings highlight the potential of ALD NiOx and SAM hybrid HSL to overcome existing barriers, advancing the commercial viability of PSC technologies.

Enhancing Performance of NiOx-Based Inverted Perovskite Solar Cells: Advances in Buried Interface Material Modification Strategy

Inverted perovskite solar cells (PSCs) have become a current research hotspot due to their advantages such as low-temperature preparation, low hysteresis, and compatibility with stacked other cells. NiOx, as a metal oxide hole transport layer material, is widely used in inverted PSCs. However, challenges such as high defect density, low intrinsic conductivity, and unfavorable valence band mismatch at the NiOx/perovskite interface hinder further improvement of device performance. Therefore, enhancing the buried interface between NiOx and perovskite layers is crucial for optimizing performance. This review systematically categorizes materials based on their types, including organic small molecules, self-assembled monolayers (SAMs), polymers, and salts. Additionally, it incorporates other strategies, such as the introduction of low-dimensional materials, metal doping, and advancements in NiOx deposition technology. By reviewing the materials and technologies used in the past 2 years, this article aims to provide insights for enhancing the buried interface to achieve more efficient and stable NiOx-based PSCs. Finally, we also discuss future directions and challenges.

Highly conductive and homogeneous NiOx nanoparticles for stable and efficient flexible perovskite solar cells

We present a facile strategy to improve the conductivity and homogeneousness of nickel oxide nanoparticles (NiOx NPs). The inverted flexible perovskite solar cells (F-PSCs) prepared with NiOx achieved impressive efficiencies of 22.68% under AM 1.5G and 35.59% under 1000 lux, respectively.

Unveiling Popular PEDOT:PSS-Derived Composition Segregation Effect in Tin-Lead Mixed Perovskite Solar Cells and Elimination

As the most popular hole-transport material for promising tin-lead mixed perovskite (TLP) solar cells, poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) would cause the composition segregation of TLP, besides exacerbating degradation and parasitic absorption reported previously. However, the segregation phenomenon is now crucial but was rarely discussed previously, and the mechanism behind it was hardly investigated. In this work, we reveal unambiguously that PSS with a sulfonic acid group in PEDOT:PSS has the propensity to coordinate Sn prior to Pb and causes the uneven nucleation at the surface of PEDOT:PSS, further affecting the growth of the TLP film. This resulted in severe tin enrichment, and voids frequently occurred at the buried interfacial layer; herein, the Sn/Pb distribution was uneven through the TLP film. To address this concern, we designed 4-(10H-phenoxazin-10-yl)butyl)phosphonic acid (PXZPA) to exclude that negative effect. For the Cs0.1FA0.7MA0.2Sn0.3Pb0.7I3 TLP material with a bandgap of 1.30 eV, the defect density declined obviously from 1.33 × 1016 cm-3 to 5.78 × 1015 cm-3, and the champion device conversion efficiency surged remarkably from 17.27% to 22.43%.

Buried hole-selective interface engineering for high-efficiency tin-lead perovskite solar cells with enhanced interfacial chemical stability

Mixed Sn-Pb perovskites are attracting significant attention due to their narrow bandgap and consequent potential for all-perovskite tandem solar cells. However, the conventional hole transport materials can lead to band misalignment or induce degradation at the buried interface of perovskite. Here we designed a self-assembled material 4-(9H-carbozol-9-yl)phenylboronic acid (4PBA) for the surface modification of the substrate as the hole-selective contact. It incorporates an electron-rich carbazole group and conjugated phenyl group, which contribute to a substantial interfacial dipole moment and tune the substrate's energy levels for better alignment with the Sn-Pb perovskite energy levels, thereby promoting hole extraction. Meanwhile, enhanced perovskite crystallization and improved contact at bottom of the perovskite minimized defects within perovskite bulk and at the buried interface, suppressing non-radiative recombination. Consequently, Sn-Pb perovskite solar cells using 4PBA achieved efficiencies of up to 23.45%. Remarkably, the 4PBA layer provided superior interfacial chemical stability, and effectively mitigated device degradation. Unencapsulated devices retained 93.5% of their initial efficiency after 2000 h of shelf storage.

Defect Passivation and Stress Release Strategies for Inverted Perovskite Solar Cells Based on the Low-Pressure-Assisted Solution Process

Perovskite solar cells (PSCs) have attracted much attention in the global photovoltaic field due to their excellent optoelectronic properties. However, the intrinsic crystalline properties and the preparation methods of perovskites result in numerous defects and residual stress in the perovskite film. To address this issue, the additive 3-methylthio-1-propylammonium bromide (3MeSPABr) was added to the perovskite precursor solution, and PSCs with an inverted structure via a low-pressure-assisted solution process were fabricated. The additive was found to interact with the perovskite through strong coordination and hydrogen bonding, passivate defects, and alleviate residual tensile stress. The power conversion efficiency (PCE) of the PSCs as high as 21.99% was obtained. Besides, the addition of 3MeSPABr also increases the hydrophobicity of the perovskite film and improves the stability of the PSCs.

Deciphering the Impact of Aromatic Linkers in Self-Assembled Monolayers on the Performance of Monolithic Perovskite/Si Tandem Photovoltaic

Aromatic linker-constructed self-assembled monolayers (Ar-SAMs) with enlarged dipole moment can modulate the work function of indium tin oxide (ITO), thereby improving hole extraction/transport efficiency. However, the specific role of the aromatic linkers between the polycyclic head and the anchoring groups of SAMs in determining the performance of perovskite solar cells (PSCs) remains unclear. In this study, we developed a series of phenothiazine-based Ar-SAMs to investigate how different aromatic linkers could affect molecular stacking, the regulation of substrate work function, and charge carrier dynamics. When served as hole-selective layers (HSLs) in PSCs and monolithic perovskite/silicon tandem solar cells (P/S-TSCs), we found that the Ar-SAM with naphthalene linker along the 2,6-position axis (β-Nap) could form dense and highly ordered HSLs, enhancing interfacial interactions and favoring optimal energy level alignment with the perovskite films. Using this strategy, the optimized wide-band gap PSCs achieved an impressive power conversion efficiency (PCE) of 21.86 % with negligible hysteresis, utilizing a 1.68 eV perovskite. Additionally, the encapsulated devices demonstrated enhanced stability under damp-heat conditions (ISOS-D-2, 50 % RH, 65 °C) with a T91 of 1000 hours. Notably, the fabricated P/S-TSCs, based on solution-processed micron-scale textured silicon heterojunction (SHJ) solar cells, achieved an efficiency of 28.89 % while maintaining outstanding reproducibility. This strategy holds significant promise for developing aromatic linking groups to enhance the hole selectivity of SAMs.

Novel quantitative valuation of hybrid perovskite solar cells

As an emerging photovoltaic technology, hybrid perovskite solar cells (PSCs) have achieved excellent performance through rapid development in recent years. High power conversion efficiency (PCE) and excellent stability further promote the commercialization of PSCs. To date, the perovskite light-harvesting active materials are diversified and the device fabrication process is also various. Considered the fabrication costs and steps of PSCs based on different active materials, the quantitative valuation of different hybrid PSCs with PCE above 20% is implemented using data envelopment analysis (DEA) for the first time. This valuation mainly focuses on the inputs (cost and fabrication steps) and outputs (PCE and stability). No weights are needed during the whole analytical process. This ensures the convenience and ease of operation of the analysis, promoting the universality of this method. The results show a detailed analysis of different PSCs from an economic perspective and develop a new way to evaluate PSCs. Meanwhile, the results and this novel valuation method will provide promising guidance for the commercialization of PSCs.

Controllable Heavy n-type Behaviours in Inverted Perovskite Solar Cells with Non-Conjugated Passivants

Interfacial issues between the perovskite film and electron transport layer greatly limit the efficiency and stability of inverted (p-i-n) perovskite solar cells (PSCs). Despite organic ammonium passivants have been widely established as interfacial layers, they failed to improve electron extraction. Here, we reported that the heavy n-type characteristics in a low band gap perovskite film could be modulated by incorporating non-conjugated ammonium passivants with strong electron-withdrawing abilities. This resulted in a significant enhancement of electron extraction in the heavily n-type doped perovskite. The passivant-treated PSCs exhibited a power conversion efficiency of 25.74 % with an excellent fill factor of 85.4 % and a high open-circuit voltage of 1.166 V, which are significantly higher than that of the control device. The unencapsulated devices maintained 88 % of their initial PCEs after 1,200 hours at 85 °C.

Tailoring Buried Interface and Minimizing Energy Loss Enable Efficient Narrow and Wide Bandgap Inverted Perovskite Solar Cells by Aluminum Glycinate Based Organometallic Molecule

Rational regulation of Me-4PACz/perovskite interface has emerged as a significant challenge in the pursuit of highly efficient and stable perovskite solar cells (PSCs). Herein, an organometallic molecule of aluminum glycinate (AG) that contained amine (-NH2) and aluminum hydroxyl (Al-OH) groups is developed to tailor the buried interface and minimize interface-driven energy losses. The Al-OH groups selectively bonded with unanchored O═P-OH and bare NiO-OH to optimize the surface morphology and energy levels, while the -NH2 group interacted specifically with Pb2+ to retard perovskite crystallization, passivate buried Pb-related defects, and release residual interface stress. These interactions facilitate the interface carrier extraction and reduce interface-driven energy losses, thereby realizing a balanced charge carrier transport. Consequently, AG-modified narrow bandgap (1.55 eV) PSC demonstrates an efficiency of 26.74% (certified 26.21%) with a fill factor of 86.65%; AG-modified wide bandgap (1.785 eV) PSC realizes 20.71% champion efficiency with excellent repeatability. These PSCs maintain 91.37%, 91.92%, and 92.00% of their initial efficiency after aging in air atmosphere, the nitrogen-filled atmosphere at 85 °C, and continuously tracking at the maximum power-point under one-sun illumination (100 mW cm-2) for 1200 h, respectively.

Regulation of Interface Schottky Barrier and Photoelectric Properties in Carbon-Based HTL-Free Perovskite Solar Cells

Carbon-based hole transport layer (HTL)-free perovskite solar cells (C-PSCs) receive a lot of attention because of their simplified preparation technology, low price, and good hydrophobicity. However, the Schottky junction formed at the interface between perovskite and carbon poles affects the photogenerated carrier extraction and conversion efficiency. In this paper, 4-trifluoromethyl-2-pyridinecarboxylic acid (TPCA) is used to modify the perovskite films. The introduction of TPCA can reduce the p-type Schottky barrier height (p-SBH) and thin the Schottky barrier width W, which greatly improves the hole transport ability and tunneling probability. Meanwhile, the n-type Schottky barrier height (n-SBH) shows a rising trend, which prevents the reverse electron transport to carbon, suppresses unnecessary carrier complexes, and greatly improves the device's optoelectronic performance. Besides, the pyridine nitrogen and C = O in TPCA interact with Pb2+ to raise the crystal quality of perovskite films while inhibiting nonradiative recombination. The results show that compared with the pristine device's 11.45% photoelectric conversion efficiency （PCE), the TPCA-modified device achieves 13.64% PCE. The device's long-term stability significantly improved post-TPCA modification. After 720 h of storage at room temperature and 40-60% relative humidity in the air, the unencapsulated device retained 77% of its initial efficiency.

Oriented Molecular Dipole-Enabled Modulation of NiOx/Perovskite Interface for Pb-Sn Mixed Inorganic Perovskite Solar Cells

Nickel oxide (NiOx) is considered as a potential hole transport material in the fabrication of lead-tin (Pb-Sn) perovskite solar cells (PSCs) for tandem applications. However, the energy level mismatch and unfavorable redox reactions between Ni≥3+ species and Sn2+ at the NiOx/perovskite interface pose challenges. Herein, high-performance Pb-Sn-based inorganic PSCs are demonstrated by modulating the NiOx/perovskite interface with a multifunctional 4-aminobenzenesulfonic acid (4-ABSA) interlayer. The 4-ABSA interlayer induces the formation of an oriented dipole moment directed from NiOx to perovskite, effectively elevating the valance band maximum of the NiOx film, thus balancing the energy level difference and promoting charge carrier extraction of the device. Moreover, the 4-ABSA molecules interact with both NiOx and perovskite, suppressing the reaction of highly active Ni≥3+ species with perovskites while regulating perovskite crystallization. This results in perovskite films with reduced defect density and enlarged grains. Consequently, a remarkable device efficiency of 17.4% is obtained, representing the highest reported value for Pb-Sn-based inorganic PSCs thus far. Furthermore, the 4-ABSA interlayer enhances the UV-radiation and operational stability of the resulting devices, maintaining over 80% and 90% of the initial efficiency after 240 h of UV-light exposure and 480 h of 1 sun illumination, respectively.

25.91%-Efficiency and Durable Inverted Perovskite Solar Cells Enabled by a Multifunctional Molecule Mediated Precursor Engineering

The stability of the precursor is essential for producing high-quality perovskite films with minimal non-radiative recombination. In this study, methionine sulfoxide (MTSO), which features multiple electron-donation sites, is strategically chosen as a precursor stabilizer and crystal growth mediator for inverted perovskite solar cells (PSCs). MTSO stabilizes the precursor by inhibiting the oxidation of iodide ions and passivates charged traps through coordination and hydrogen bonding interactions. This leads to enhanced crystallinity, reduced non-radiative recombination, and decreased internal residual stress in perovskite film. As a result, remarkable power conversion efficiencies of 25.91% (certified 25.76%) with a minimal voltage deficit of 0.36 V for a 0.09-cm2 inverted PSC, and 21.96% for a 12.96-cm2 (active area) perovskite minimodule, have been achieved, respectively. Furthermore, the unencapsulated devices demonstrated excellent long-term thermal aging and operational stability, retaining over 90% and 92% of their original efficiencies after 500 h of continuous thermal aging at 85 °C and 2500 h of continuous maximum power point tracking under 1 sun (white light LED array) illumination at 30 ± 5 °C. This study underscores the importance of the rational design of functional molecules for stabilizing the precursor and regulating the crystallization of perovskite films, advancing the practical development of PSCs.

Biomass Derived Self-Doped Carbon Nanosheets Enable Robust Hole Transport Layers with Ion Buffer for Perovskite Solar Cells

The diffusion of iodine species and lead leakage during device degradation represent the main obstacles restricting the commercial application of perovskite solar cells (PSCs). Cobalt loaded ultrathin carbon nanosheets (Co(III)-CNS) derived from biomass are prepared as ion buffer material to construct robust hole transport layers (HTLs). The carbon nanosheets containing trivalent cobalt ions can facilitate the oxidation of the hole transport material while preserving the structural integrity and electrical properties of HTLs under thermal stress, thereby ensuring efficient carrier transport. The two-dimensional ultrathin graphitized lamellar structure of Co(III)-CNS is conducive to alleviate the corrosive effects of the outward diffusion of iodine species on HTLs and silver electrodes, while avoiding irreversible degradation of PSCs. With the improvement of HTL composition and the related interfaces, Co(III)-CNS doped devices can maintain intact device structure under thermal stress and remain above 80 % of the original power conversion efficiency (PCE) after thermal aging at 85 °C for 720 h. Notably, the chemical interactions between heteroatoms of self-doped carbon nanosheets and the mobile lead ions can effectively alleviate lead leakage and avoid the potential impacts of device degradation on ecosystem. Ultimately, the Co(III)-CNS doped PSCs with enhanced thermal stability exhibit a champion PCE of 22.32 %.

Linking Nanoscopic Insights to Millimetric-Devices in Formamidinium-Rich Perovskite Photovoltaics

Halide-perovskite semiconductors have a high potential for use in single-junction and tandem solar cells. Despite their unprecedented rise in power conversion efficiencies (PCEs) for photovoltaic (PV) applications, it remains unclear whether perovskite solar modules can reach a sufficient operational lifetime. In order to make perovskite solar cells (PSCs) commercially viable, a fundamental understanding of the relationship between their nanostructure, optoelectronic properties, device efficiency, and long-term operational stability/reliability needs to be established. In this review, the phase instabilities in state-of-the-art formamidinium (FA)-rich perovskite absorbers is discussed. Furthermore, the concerted efforts are summarized in this prospect, covering aspects from fundamental research to device engineering. Subsequently, a critical analysis of the dictating impact of the nanoscale landscape of perovskite materials on their resulting intrinsic stability is provided. Finally, the remaining challenges in the field are assessed and future research directions are proposed for improving the operational lifetimes of perovskite devices. It is believed that these approaches, which bridge nanoscale structural properties to working solar cell devices, will be critical to assessing the realization of a bankable PSC product.

Enlarging moment and regulating orientation of buried interfacial dipole for efficient inverted perovskite solar cells

Carrier transport and recombination at the buried interface of perovskite have seriously restricted the further development of inverted perovskite solar cells (PSCs). Herein, an interfacial dipolar chemical bridge strategy to address this issue is presented. 2-(Diphenylphosphino) acetic acid (2DPAA) is selected as the linker to reconstruct the interfacial dipole, which effectively enlarges the interfacial dipole moment to 5.10 D and optimizes to a positive dipole orientation, thereby accelerating vertical hole transport, suppressing nonradiative recombination and promoting the perovskite crystallization. The champion inverted device yields a high power conversion efficiency (PCE) of 26.53% (certified 26.02%). Moreover, this strategy is extended to the wide-bandgap perovskite and large-area devices, which delivers high PCEs of 22.02% and 24.11%, respectively. The optimized devices without encapsulation also demonstrate great long-term shelf and operational stability. Our work highlights the importance of interfacial dipole moment and orientation at the buried interface to realize efficient and stable inverted PSCs.

Dimensional Regulation of Organic n-Type Dopants for Highly Efficient Perovskite Solar Cells and Modules

A strong n-type perovskite layer is crucial in achieving high open-circuit voltage (VOC) and power conversion efficiency (PCE) in the p-i-n solar cells, as the weak n-type perovskites result in a loss of VOC, and the p-type perovskites contain numerous electron traps that cause the severe carrier recombination. Here, three types of perylene diimide (PDI) based small molecule dopants with different dimensions, including 1D-PDI, 2D-PDI, and 3D-PDI are designed, to produce heavier n-type perovskites. The PDI-based molecules with Selenium atoms have a strong electron-donating ability, effectively enlarging the quasi-Fermi level splitting within the perovskites. Besides, the PDI molecules can coat the surface of the perovskite crystal to form the lattice cage through their conjugate skeletons, which passivates the trap states and improves the n-doping efficiency, as well as the stabilities of perovskites and related devices. With the addition of the 2D-PDI, the small-area solar cells achieved a PCE of 26.06% (25.44% certified) with a high VOC of 1.18 V and a remarkable fill factor of 87.23%. Furthermore, the rigid and flexible perovskite solar modules yielded high PCEs of 21.48% and 20.71%, respectively. This dimensional regulation strategy provides useful guidance for effective n-type doping and high-performance p-i-n solar cells.

Stabilization Strategies of Buried Interface for Efficient SAM-Based Inverted Perovskite Solar Cells

In recent years, self-assembled monolayers (SAMs) anchored on metal oxides (MO) have greatly boosted the performance of inverted (p-i-n) perovskite solar cells (PVSCs) by serving as hole-selective contacts due to their distinct advantages in transparency, hole-selectivity, passivation, cost-effectiveness, and processing efficiency. While the intrinsic monolayer nature of SAMs provides unique advantages, it also makes them highly sensitive to external pressure, posing a significant challenge for long-term device stability. At present, the stability issue of SAM-based PVSCs is gradually attracting attention. In this minireview, we discuss the fundamental stability issues arising from the structural characteristics, operating mechanisms, and roles of SAMs, and highlight representative works on improving their stability. We identify the buried interface stability concerns in three key aspects: 1) SAM/MO interface, 2) SAM inner layer, and 3) SAM/perovskite interface, corresponding to the anchoring group, linker group, and terminal group in the SAMs, respectively. Finally, we have proposed potential strategies for achieving excellent stability in SAM-based buried interfaces, particularly for large-scale and flexible applications. We believe this review will deepen understanding of the relationship between SAM structure and their device performance, thereby facilitating the design of novel SAMs and advancing their eventual commercialization in high-efficiency and stable inverted PVSCs.

Simultaneous Suppression of Multilayer Ion Migration via Molecular Complexation Strategy toward High-Performance Regular Perovskite Solar Cells

The migration and diffusion of Li+, I- and Ag impedes the realization of long-term operationally stable perovskite solar cells (PSCs). Herein, we report a multifunctional and universal molecular complexation strategy to simultaneously stabilize hole transport layer (HTL), perovskite layer and Ag electrode by the suppression of Li+, I- and Ag migration via directly incorporating bis(2,4,6-trichlorophenyl) oxalate (TCPO) into HTL. Meanwhile, TCPO co-doping results in enhanced hole mobility of HTL, advantageous energy band alignment and mitigated interfacial defects, thereby leading to facilitated hole extraction and minimized nonradiative recombination losses. TCPO-doped regular device achieves a peak power conversion efficiency (PCE) of 25.68 % (certified 25.59 %). The unencapsulated TCPO doped devices maintain over 90 % of their initial efficiencies after 730 h of continuous operation under one sun illumination, 2800 h of storage at 30 % relative humidity, and 1200 h of exposure to 65 °C, which represents one of the best stabilities reported for regular PSCs. This work provides a new approach to enhance the PCE and long-term stability of PSCs by host-guest complexation strategy via rational design of multifunctional ligand molecules.

Rationally designed universal passivator for high-performance single-junction and tandem perovskite solar cells

Interfacial trap-assisted nonradiative recombination hampers the development of metal halide perovskite solar cells (PSCs). Herein, we report a rationally designed universal passivator to realize highly efficient and stable single junction and tandem PSCs. Multiple defects are simultaneously passivated by the synergistic effect of anion and cation. Moreover, the defect healing effect is precisely modulated by carefully controlling the number of hydrogen atoms on cations and steric hindrance. Due to minimized interfacial energy loss, L-valine benzyl ester p-toluenesulfonate (VBETS) modified inverted PSCs deliver a power conversion efficiency (PCE) of 26.28% using vacuum flash processing technology. Moreover, by suppressing carrier recombination, the large-area modules with an aperture area of 32.144 cm2 and perovskite/Si tandem solar cells coupled with VBETS passivation deliver a PCE of 21.00% and 30.98%, respectively. This work highlights the critical role of the number of hydrogen atoms and steric hindrance in designing molecular modulators to advance the PCE and stability of PSCs.

Tailoring pyridine bridged chalcogen-concave molecules for defects passivation enables efficient and stable perovskite solar cells

Suppressing deep-level defects at the perovskite bulk and surface is indispensable for reducing the non-radiative recombination losses and improving efficiency and stability of perovskite solar cells (PSCs). In this study, two Lewis bases based on chalcogen-thiophene (n-Bu4S) and selenophene (n-Bu4Se) having tetra-pyridine as bridge are developed to passivate defects in perovskite film. The uncoordinated Pb2+ and iodine vacancy defects can interact with chalcogen-concave group and pyridine group through the formation of the Lewis acid-base adduct, particularly both the defects can be surrounded by concave molecules, resulting in effective suppression charge recombination. This approach enables a power conversion efficiency (PCE) as high as 25.37% (25.18% certified) for n-i-p PSCs with stable operation at 65 °C and 1-sun illumination for 1300 hours in N2 (ISOS-L-2 protocol), retaining 94% of the initial efficiency. Our work provides insight into the bowl-shaped Lewis base in defects passivation by coordinated strategy for high-performance photovoltaic devices.

Cyclic Multi-Site Chelation for Efficient and Stable Inverted Perovskite Solar Cells

Trap-assisted non-radiative recombination losses and moisture-induced degradation significantly impede the development of highly efficient and stable inverted (p-i-n) perovskite solar cells (PSCs), which require high-quality perovskite bulk. In this research, we mitigate these challenges by integrating thermally stable perovskite layers with Lewis base covalent organic frameworks (COFs). The ordered pore structure and surface binding groups of COFs facilitate cyclic, multi-site chelation with undercoordinated lead ions, enhancing the perovskite quality across both its bulk and grain boundaries. This process not only reduces defects but also promotes improved energy alignment through n-type doping at the surface. The inclusion of COF dopants in p-i-n devices achieves power conversion efficiencies (PCEs) of 25.64 % (certified 24.94 %) for a 0.0748-cm2 device and 23.49 % for a 1-cm2 device. Remarkably, these devices retain 81 % of their initial PCE after 978 hours of accelerated aging at 85°C, demonstrating remarkable durability. Additionally, COF-doped devices demonstrate excellent stability under illumination and in moist conditions, even without encapsulation.

Small-Molecule Hole Transport Materials for >26% Efficient Inverted Perovskite Solar Cells

Chemically modifiable small-molecule hole transport materials (HTMs) hold promise for achieving efficient and scalable perovskite solar cells (PSCs). Compared to emerging self-assembled monolayers, small-molecule HTMs are more reliable in terms of large-area deposition and long-term operational stability. However, current small-molecule HTMs in inverted PSCs lack efficient molecular designs that balance both the charge transport capability and interface compatibility, resulting in a long-standing stagnation of power conversion efficiency (PCE) below 24.5%. Here, we report the comprehensive design of HTMs' backbone and functional groups, which optimizes a simple planar linear molecular backbone with a high mobility exceeding 7.1 × 10-4 cm2 V-1 S-1 and enhances its interface anchoring capability. Owing to the improved surface properties and anchoring effects, the tailored HTMs enhance the interface contact at the HTM/perovskite heterojunction, minimizing nonradiative recombination and transport loss and leading to a high fill factor of 86.1%. Our work has overcome the persistent efficiency bottleneck for small-molecule HTMs, particularly for large-area devices. Consequently, the resultant PSCs exhibit PCEs of 26.1% (25.7% certified) for a 0.068 cm2 device and 24.7% (24.4% certified) for a 1.008 cm2 device, representing the highest PCE for small-molecule HTMs in inverted PSCs.

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.

Lattice Matching Anchoring of Hole-Selective Molecule on Halide Perovskite Surfaces for n-i-p Solar Cells

Exploiting the self-assembled molecules (SAMs) as hole-selective contacts has been an effective strategy to improve the efficiency and long-term stability of perovskite solar cells (PSCs). Currently, research works are focusing on constructing SAMs on metal oxide surfaces in p-i-n PSCs, but realizing a stable and dense SAM contact on halide perovskite surfaces in n-i-p PSCs is still challenging. In this work, the hole-selective molecule for n-i-p device is developed featuring a terephthalic methylammonium core structure that possesses double-site anchoring ability and a matching diameter (6.36 Å) with the lattice constant of formamidinium lead iodide (FAPbI3) perovskite (6.33 Å), which facilitates an ordered and full-coverage SAM atop FAPbI3 perovskite. Moreover, theoretical calculations and experimental results indicate that compared to the frequently used acid or ester anchoring groups, this ionic anchoring group with a dipolar charge distribution has much larger adsorption energy on both organic halide terminated and lead halide terminated surfaces, resulting in synergistic improvement of carrier extraction and defect passivation ability. Benefiting from these merits, the efficiency of PSCs is increased from 21.68% to 24.22%. The long-term operational stability under white LED illumination (100 mW cm-2) and at a high temperature of 85 °C is also much improved.

Heptamethine Cyanine Dye-Doped Single-Walled Carbon Nanotube Electrodes for Improving Performance of HTL-Free Perovskite Solar Cells

Perovskite solar cell (PSC) technology holds great promise with continuously improving power conversion efficiency; however, the use of metal electrodes hinders its commercialization and the development of tandem designs. Although single-walled carbon nanotubes (SWCNTs), as one-dimensional materials, have the potential to replace metal electrodes in PSCs, their poor conductivity still limits their application. In this study, the near-infrared (NIR)-absorbing anionic heptamethine cyanine dye-doped SWCNTs functioned in a dual role as an efficient charge-selective layer and electrode in PSCs. Benefiting from the improvement in conductivities and matched energy level of doped-SWCNT, the dual-role SWCNT electrodes applied to PSCs achieved a better performance than the undoped PSCs with a higher short circuit current (JSC) and fill factor (FF).

Enhancing Hole Transport Uniformity for Efficient Inverted Perovskite Solar Cells through Optimizing Buried Interface Contacts and Suppressing Interface Recombination

[4-(3,6-dimethyl-9H-carbazol-9yl)butyl]phosphonic acid (Me-4PACz) self-assembly material has been recognized as a highly effective approach for mitigating nickel oxide (NiOx) surface-related challenges in inverted perovskite solar cells (IPSCs). However, its uneven film generation and failure to effectively passivate the buried interface defects limit the device's performance improvement potential. Herein, p-xylylenediphosphonic acid (p-XPA) containing bilateral phosphate groups (-PO3H2) is introduced as an interface layer between the NiOx/Me-4PACz and the perovskite layer. P-XPA can flatten the surface of hole transport layer and optimize interface contact. Meanwhile, p-XPA achieves better energy level alignment and promotes interfacial hole transport. In addition, the bilateral -PO3H2 of p-XPA can chelate with Pb2+ and form hydrogen bond with FA+ (formamidinium cation), thereby suppressing buried interface non-radiative recombination loss. Consequently, the IPSC with p-XPA buried interface modification achieves champion power conversion efficiency of 25.87 % (certified at 25.45 %) at laboratory scale (0.0448 cm2). The encapsulated target device exhibits better operational stability. Even after 1100 hours of maximum power point tracking at 50 °C, its efficiency remains at an impressive 82.7 % of the initial efficiency. Molecules featuring bilateral passivation groups optimize interfacial contact and inhibit interfacial recombination, providing an effective approach to enhancing the stability and efficiency of devices.

Elucidating the Impact of Buried Interface Engineering on Perovskite Properties and Stability in Inverted Perovskite Solar Cells

Buried-interface engineering is crucial in the fabrication of perovskite solar cells (PSCs) due to its effectiveness in facilitating the deposition of perovskite absorbers. This technique is especially significant in inverted PSCs (IPSCs) where the dewetting materials are normally used as the bottom hole transporters. Here, we investigate the impact of buried-interface techniques on the optical and mechanical behavior of perovskites and the overall stability of IPSCs. Our findings demonstrate that the chemical treatment with fluorene-based conjugated polyelectrolyte (e.g., PFN-Br), in contrast to the physical UV-ozone method, induces distinct dendrite-like patterns at the buried interface. These changes profoundly impact the optical properties of the perovskite films, evidenced by red-shifted photoluminescence in these regions. Furthermore, the dendritic morphologies are shown to affect the mechanical properties of the as-crystallized perovskite films, such as a reduction in Young's modulus/hardness, which in turn modulate the device performance. The photovoltaic data indicate that these dendrite-like patterns are beneficial for the initial efficiencies but compromise the long-term stability of the derived IPSCs. This study provides valuable insights into buried-interface engineering strategies for achieving efficient and stable IPSCs.

One-Stone-For-Three-Birds Strategy Using a Fullerene Modifier for Efficient and Stable Inverted Perovskite Solar Cells

The electron extraction from perovskite/C60 interface plays a crucial role in influencing the photovoltaic performance of inverted perovskite solar cells (PSCs). Here, we develop a one-stone-for-three-birds strategy via employing a novel fullerene derivative bearing triple methyl acrylate groups (denoted as C60-TMA) as a multifunctional interfacial layer to optimize electron extraction at the perovskite/C60 interface. It is found that the C60-TMA not only passivates surface defects of perovskite via coordination interactions between C=O groups and Pb2+ cations but also bridge electron transfer between perovskite and C60. Moreover, it effectively induces the secondary grain growth of the perovskite film through strong bonding effect, and this phenomenon has never been observed in prior art reports on fullerene related studies. The combination of the above three upgrades enables improved perovskite film quality with increased grain size and enhanced crystallinity. With these advantages, C60-TMA treated PSC devices exhibit a much higher power conversion efficiency (PCE) of 24.89 % than the control devices (23.66 %). Besides, C60-TMA benefits improved thermal stability of PSC devices, retaining over 90 % of its initial efficiency after aging at 85 °C for 1200 h, primarily due to the reinforced interfacial interactions and improved perovskite film quality.