Stabilizing black-phase formamidinium perovskite formation at room temperature and high humidity

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.

Revealing Collaborative Effects of Binary Additives on Regulating Precursor Crystallization Toward Highly Efficient Perovskite Solar Cells

Fabricating high-quality perovskite layers is essential for achieving high-performance solar cells. Considering the significant advancements made in additive engineering for optimizing perovskite crystallization using single additive, exploring the collaborative effect of dual additives on precursor for perovskite crystallization may be an effective way for further advancing device performance. Herein, a binary additives strategy is proposed, where phenylmethylammonium iodide (PMAI) and [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) are introduced into the precursor. Compared with the precursor with no additives or a single additive (PMAI or 2PACz), the use of dual additives more effectively cleaves edge-shared Pb-I octahedra to expedite the transformation from PbI2 to PbI3 - complexes as prenucleation clusters and produces much larger colloidal particles with accelerated nucleation. Concurrently, the crystallization in both spin-coating and annealing processes is significantly retarded due to the stronger interaction between perovskite and binary additives. Benefiting from such rapid nucleation and slow crystallization, high-quality perovskite layer with larger-sized crystals and fewer defects is formed, resulting in mitigated microstrain, enhanced charge extraction, and suppressed nonradiative recombination. Consequently, the device derived from the use of dual additives could achieve an impressive efficiency of 26.05% (certified 25.49%) and retained 90% of its initial efficiency after 1200 h of maximum power point tracking.

Perovskite Solar Cells and Light Emitting Diodes: Materials Chemistry, Device Physics and Relationship

Solution-processed perovskite solar cells (PSCs) and perovskite light emitting diodes (PeLEDs) represent promising next-generation optoelectronic technologies. This Review summarizes recent advancements in the application of metal halide perovskite materials for PSC and PeLED devices to address the efficiency, stability and scalability issues. Emphasis is placed on material chemistry strategies used to control and engineer the composition, deposition process, interface and micro-nanostructure in solution-processed perovskite films, leading to high-quality crystalline thin films for optimal device performance. Furthermore, we retrospectively compare the device physics of PSCs and PeLEDs, their working principles and their energy loss mechanisms, examining the similarities and differences between the two types of devices. The reciprocity relationship suggests that a great PSC should also be a great PeLED, motivating the search for interconverting photoelectric bifunctional devices with maximum radiative recombination and negligible non-radiative recombination. Specific requirements of PSCs and PeLEDs in terms of bandgap, thickness, band alignment and charge transport to achieve this target are discussed in detail. Further challenges and issues are also illustrated, together with prospects for future development. Understanding these fundamentals, embracing recent breakthroughs and exploring future prospects pave the way toward the rational design and development of high-performance PSC and PeLED devices.

Dual-Interface Passivation of Wide-Bandgap Perovskite Films for Efficient Four-Terminal Perovskite-Organic Tandem Solar Cells

Interface defects in perovskite solar cells (PSCs) can significantly impair device efficiency by promoting nonradiative recombination, hindering charge transport, and facilitating ion migration. In this work, we introduce a dual-interface passivation strategy utilizing 2-(N-morpholino)ethanesulfonic acid potassium (MESK) and octylammonium iodide (OAI), targeting both the electron transport layer (ETL)/perovskite and perovskite/hole transport layer (HTL) interfaces to enhance the efficiency of wide-bandgap PSCs based on FA0.8Cs0.2Pb(I0.6Br0.4)3 with a bandgap of 1.77 eV. The sulfonic group in MESK passivates bottom interface defects through coordination with Pb ions, while the amine group in OAI interacts with Pb and halide ions to effectively passivate top interface defects. The dual-interface passivation strategy improves perovskite crystallinity, enlarges grain size, and reduces nonradiative recombination. As a result, the performance of PSCs is significantly enhanced, achieving a power conversion efficiency (PCE) of 23.69% in a four-terminal (4T) perovskite-organic tandem solar cell (TSC), which provides a promising and sustainable solution for the commercialization of TSCs.

Homogenization and Rapid Oxidation of Spiro-OMeTAD with Ionic Liquids for Efficient Perovskite Solar Cells

Spiro-OMeTAD is widely recognized as the most effective hole transport layer (HTL) for n-i-p perovskite solar cells (PSCs), which typically requires doping with LiTFSI to overcome its low inherent conductivity. However, the doping takes a prolonged oxidation (≈24 h) in an ambient atmosphere, hindering the commercial development. Moreover, the aggregation of LiTFSI leads to poor conductivity and accelerated degradation of the HTL, which are often ignored. This study introduces the long-chain ionic liquid 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (OMIMTFSI) as a multifunctional additive to mitigate the aggregation of LiTFSI and promote the oxidation of Spiro-OMeTAD simultaneously. The strong electrostatic interactions between OMIM+ and LiTFSI, coupled with the dispersion effect of OMIM+ in chlorobenzene, effectively hamper the aggregation of LiTFSI, beneficial for uniform doping and enhanced conductivity. The OMIM+ also facilitates rapid oxidation of Spiro-OMeTAD by attracting lone pair electrons from the triphenylamine group. As a result, the power conversion efficiency of PSCs processed in air is significantly improved from 21.48% to 24.04% with enhanced stability, maintaining over 80% of initial values after storing in air for 1360 h or under light and heat treatment for 500 h. This strategy provides valuable insights of designing lithium salt-doped Spiro-OMeTAD for efficient and stable PSCs.

Cyanovinyl Phosphonic Acid Based Molecular Additives for Highly Efficient and Stable Formamidinium-Cesium Lead Lodide Perovskite Solar Cells

Formamidinium-cesium lead iodide perovskites (FA1-xCsxPbI3, 0 < x < 0.1) are promising solar cell absorber materials with favorable bandgap and high thermal stability. However, the fabrication of high-quality FA1-xCsxPbI3 films with large grain size, stable black phase, uniform cations distribution, and minimal defects remains challenging. Here, the efficacy of cyanovinyl phosphonic acid (CPA) based molecular additives in fabricating high-quality FA0.95Cs0.05PbI3 films is reported. The CPA unit shows strong interactions with all species of lead iodide (PbI2), formamidinium iodide (FAI), and cesium iodide (CsI) in the precursor solution, thus significantly alleviating the inhomogeneous crystallization in this mixed-cation system. The resulting FA0.95Cs0.05PbI3 films exhibit enlarged grain size and homogenized cation distribution, and the presence of CPA-based molecules in final perovskite films enhances optoelectronic qualities and photostability owing to efficient passivation and strong interaction with perovskite. With optimizations on molecular size and adding concentrations, inverted structured perovskite solar cells based on an optimal molecular additive (Ph-CPA) achieve power conversion efficiencies (PCEs) up to 26.25%. Moreover, the lifespans (T90, time corresponding to 90% of initial PCE retained) of the devices are unprecedentedly prolonged from hundreds of hours to over 1000 and 3000 h under light and thermal stresses (ISOS-L-2I, 85 °C) and operational condition (ISOS-L-1I), respectively.

Degradable Additive Couple Enable Pure and Stable Alpha-Phase FAPbI3 for Perovskite Solar Cells

Pure black-phase FAPbI3 has always been pursued because of its ideal bandgap (Eg) and high thermal stability. Here, a pair of sacrificial agents containing diethylamine hydrochloride (DEACl) and formamide (Fo) is reported, which can induce the oriented growth of black-phase FAPbI3 along (111) and will disappear by the aminolysis reaction during perovskite annealing, retaining the Eg of FAPbI3 as 1.49 eV. In addition, the tensile strain of the target FAPbI3 is found to be mitigated with a stabilized black phase due to the tilt of FA+. The devices based on the pure and stable black-phase (111)-FAPbI3 achieved a power conversion efficiency of 25.2% and 24.2% (certified 23.51%) with an aperture area of 0.09 and 1.04 cm2, respectively. After 1080 h of operation at the maximum power point under 1-sun illumination (100 mW cm-2), the devices maintained 91.68 ± 0.72% of the initial efficiencies.

Modulating Crystal Growth with Sacrificial Coordination for High-Performance Perovskite Solar Cells via Intense Pulsed Light Annealing

Intense pulsed light (IPL) annealing has emerged as a transformative technology for the high-throughput, low-cost fabrication of perovskite films, enabling the rapid conversion of precursor wet films into perovskite films within milliseconds. Despite their potential, the efficiencies of IPL-processed devices have yet to match those achieved through conventional thermal annealing (TA), primarily due to the challenges of uncontrolled crystallization and defect formation during the IPL process. In this study, a solid Lewis base additive, dodecyl methyl sulfoxide (DodecylMSO) is introduced, to modulate perovskite crystal growth and improve film morphology and uniformity under IPL conditions. DodecylMSO acts as a sacrificial additive, with X-ray photoelectron spectroscopy (XPS) confirming the majority of it is removed in the final films. Compared to the control films, DodecylMSO-modified films exhibited significantly reduced defect densities and enhanced carrier extraction and transport properties. Leveraging this approach, p-i-n perovskite solar cells (PSCs) is demonstrated with a champion power conversion efficiency of 23.5% fabricated via IPL. This sacrificial coordination strategy not only addresses key challenges in IPL processing but also opens new avenues for advancing the manufacturability and scalability of high-performance PSCs.

Stabilize Perovskite Precursors and Inhibit Intermediates for High Performing Perovskite Solar Cells

Significant power conversion efficiency (PCEs) advancements have been made in perovskite solar cells (PSCs). However, the degraded precursor can severely affect the crystallinity and reproducibility of the films, and the stability of the perovskite precursor and the intermediate phases during film growth remains a considerable hurdle. Here the saccharin sodium (SacS) is introduced into the perovskite precursor. Benefiting from the electron-rich sulfonyl (O═S═O) and carbonyl (C═O) groups, the SacS molecule formed a stable complex with lead(II) iodide (PbI2) in the precursor, which retarded the degradation and colloidal aggregation of the precursor and suppresses the formation of unfavorable intermediate phases during film growth. The strong interaction reduces the surface energy of the nuclei and promotes the formation of larger-sized nuclei, resulting in high-quality films with vertical orientation. This approach significantly improves the power conversion efficiency (PCE) of the device to 24.8% and bolsters the long-term stability.

Simultaneous Halides Oxidation Inhibition and Defects Passivation for Efficient and Stable Perovskite Solar Cells

Despite significant progress in improving the photovoltaic efficiency of perovskite solar cells (PSCs), achieving long-term operational stability remains challenging for their commercialization. Light-induced halide ion migration causes instability, oxidizing iodide into iodine. Elevated temperatures exacerbate this issue, resulting in irreversible device degradation. Here, ammonium oxalate (AO) is introduced as an additive to the perovskite precursor to prevent both the degradation of the perovskite precursor and the photo-induced degradation pathway to formamidinium iodide and PbI2 in perovskite films. AO stabilizes the precursor by inhibiting the oxidation of iodide ions (I-) and passivates charged traps through coordination and hydrogen bonding interactions, thereby enhancing crystallinity and reducing defects within the resultant perovskite films. This leads to the achievement of a higher-quality perovskite film with a low trap density and an extended carrier lifetime. In addition, the oxidation of I- within the perovskite film is inhibited, reducing the corrosion of I2 on the silver electrode and enhancing the long-term operating stability of the photovoltaic device. Consequently, the champion power conversion efficiency (PCE) of PSCs is increased from 22.19% to 24.82%. Meanwhile, the air, thermal, and light stability are also enhanced.

On-demand formation of Lewis bases for efficient and stable perovskite solar cells

In the fabrication of FAPbI3-based perovskite solar cells, Lewis bases play a crucial role in facilitating the formation of the desired photovoltaic α-phase. However, an inherent contradiction exists in their role: they must strongly bind to stabilize the intermediate δ-phase, yet weakly bind for rapid removal to enable phase transition and grain growth. To resolve this conflict, we introduced an on-demand Lewis base molecule formation strategy. This approach utilized Lewis-acid-containing organic salts as synthesis additives, which deprotonated to generate Lewis bases precisely when needed and could be reprotonated back to salts for rapid removal once their role is fulfilled. This method promoted the optimal crystallization of α-phase FAPbI3 perovskite films, ensuring the uniform vertical distribution of A-site cations, larger grain sizes and fewer voids at buried interfaces. Perovskite solar cells incorporating semicarbazide hydrochloride achieved an efficiency of 26.1%, with a National Renewable Energy Laboratory-certified quasi-steady-state efficiency of 25.33%. These cells retained 96% of their initial efficiency after 1,000 h of operation at 85 °C under maximum power point tracking. Additionally, mini-modules with an aperture area of 11.52 cm2 reached an efficiency of 21.47%. This strategy is broadly applicable to all Lewis-acid-containing organic salts with low acid dissociation constants and offers a universal approach to enhance the performance of perovskite solar cells and modules.

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.

Radical Molecular Network-Buffer Minimizes Photovoltage Loss in FAPbI₃ Perovskite Solar Cells

Formamidinium lead iodide (FAPbI₃) perovskite solar cells (PSCs) hold immense potential for high-efficiency photovoltaics, but maximizing their open-circuit voltage (VOC) remains challenging. Targeting the inherently stable {111}c-dominant facets is a promising approach for enhancing stability, but their formation typically suffers from high defect densities and disordered growth. This study introduces a novel approach using an in situ polymerizable radical molecule, ATEMPO, as an additive to address these issues. ATEMPO preferentially interacts with the {111}c perovskite facets, guiding their growth and forming a "radical molecular network-buffer" upon polymerization. The network effectively mitigates lattice strain, suppresses defect formation, enhances charge transport via redox-mediated hopping, and provides a hydrophobic barrier, significantly improving moisture resistance. This strategy yields high-quality, {111}c -oriented FAPbI₃ films, leading to a champion PCE of 25.28% with a remarkably high VOC of 1.203 V, corresponding to an energy loss (Eloss) of only 0.297 eV, among the highest VOC reported for FAPbI₃-based PSCs. Furthermore, a mini-module fabricate with an active area of 12.5 cm2 achieve a high PCE of 21.39%. the work paves the way for developing high-performance, stable PSCs with minimized photovoltage loss. Furthermore, it offers a promising strategy to enhance device longevity and address environmental concerns.

Synthesis and Chiroptical Properties of Chiral Lead Halide Molecular Clusters

Chiral lead halide molecular clusters (MCs) consisting of PbBr2, neutral achiral butylamine (BTYA), and chiral methylbenzylamine [(R/S)-MBA] with unique chiral optical properties in both the solution and solid states have been synthesized using ligand-assisted reprecipitation and depositing, separately. Ultraviolet-visible (UV-vis) electronic absorption and photoluminescence (PL) spectra show the first electronic absorption band and sharp blue emission band of the chiral MCs that peaked at 404 and 412 nm, respectively, in both solution and films. The emission asymmetry factor |glum| of the chiral MCs is 1.04 × 10-3 in solution and 2.01 × 10-3 in the film state at room temperature, indicating excellent circularly polarized luminescence (CPL) properties. This pronounced asymmetry is attributed to the chiral transfer from the chiral ligand to the BTYA-capped PbBr2 framework due to the chiral MBA ligand coordination with Pb2+. The samples exhibited excellent ambient stability for over 1 month, primarily due to strong BTYA-PbBr2 coordination. The MCs maintained their structure and CPL properties in the solid state, which is important for photonic applications.

Triple-Additive Strategy for Enhanced Material and Device Stability in Perovskite Solar Cells

The stability of the FAPbI3 perovskite phase is significantly affected by internal strain. In this report, additives in the perovskite precursor solution are designed to prevent local lattice mismatch of the resulting perovskite layer. Instead of using a conventional methylammonium chloride (Control), triple additives (Target) are introduced by considering ion association and formation energy. The out-of-plane orientation for the (100) plane is less pronounced by the triple additives compared to the Control film with a highly enhanced preferred orientation, which reduces the strain gradient and the Pb─I bond distance. Moreover, the anisotropic atomic-level lattice strain along (111) plane, associated with the α-to-δ phase transition, is more uniformly distributed by the triple additives. The triple-additive strategy demonstrates exceptional phase stability under relative humidity as high as 90% and the International Summit on Organic Photovoltaic Stability (ISOS)-L-2 protocol. The device lifetime measured under the ISOS-D-1 condition shows that the Target perovskite solar cell (PSC) maintains 95% of its initial power conversion efficiency (PCE) for over 8000 h, and the best PCE of 24.50% is achieved.

Solar-Driven High-Rate Ammonia Production from Wastewater Coupled with Plastic Waste Reforming

Solar-powered electrochemical NH3 synthesis offers the benefits of sustainability and absence of CO2 emissions but suffers from a poor solar-to-ammonia yield rate (SAY) due to a low NH3 selectivity, large bias caused by the sluggish oxygen evolution reaction, and low photocurrent in the corresponding photovoltaics. Herein, a highly efficient photovoltaic-electrocatalytic system enabling high-rate solar-driven NH3 synthesis was developed. A high-performance Ru-doped Co nanotube catalyst was used to selectively promote the nitrite reduction reaction (NO2RR), exhibiting a faradaic efficiency of 99.6% and half-cell energy efficiency of 52.3% at 0.15 V vs the reversible hydrogen electrode, delivering a high NO2RR selectivity even in electrolytes with high NO3- and low NO2- concentrations. Thus, the promoted NO2RR was coupled with the ethylene glycol oxidation reaction and a perovskite photovoltaic cell to achieve the highest SAY reported to date (146 ± 1 μmol h-1 cm-2) and stable operation.

Minimized optical/electrical energy loss for 25.1% Monolithic perovskite/organic tandem solar cells

Perovskite/organic tandem solar cells (PO-TSCs) exploit the advantages of cost-effective fabrication, orthogonal solvent processing for perovskite and organic absorber layers, and compatibility with low-temperature, high-throughput deposition techniques. However, their performance remains hampered by energy losses of subcells and interconnecting layers (ICLs). Here, an energy loss management strategy for PO-TSCs is proposed, focusing on the simultaneous regulation of defect states in perovskite front subcells and the reduction of optical and electrical losses in the ICL. The synergistic effect of hydrogen bonding and coordination interactions between the pyridinium bromide perbromide and perovskite layer effectively mitigates ion migration, thereby minimizing energy losses. Meanwhile, the optimized V2O5-based ICL structure not only demonstrates excellent transmissivity for near-infrared photons but also allows for barrier-free extraction of charge carriers. Such structure can provide a low-loss interface, facilitating light management within the bulk heterojunction, which effectively balances the current between the front and rear subcells. Taken together, the resulting PO-TSCs deliver a power conversion efficiency of 25.1% with a high open-circuit voltage of 2.10 V.

Role of Water in the Stability and Efficiency of Ionic Liquid-Based Perovskite Solar Cells

The fabrication of perovskite solar cells (PSCs) in ambient air can accelerate their industrialization. However, moisture causes severe decomposition of the perovskite materials, limiting device efficiency. Here, we demonstrate that, compared to traditional N,N-dimethylformamide-based precursor solutions, the ionic liquid methylammonium acetate (MAAc) system forms a protective layer on the perovskite surface due to the C═O···Pb and N-H···I interactions between MAAc and PbI64-, which effectively prevents direct contact between the perovskite components and water. Moreover, we show that a certain level of humidity weakens the interactions between MAAc and PbI64-, promoting the crystallization process and resulting in films with fewer defects. PSCs based on MAAc achieved a power conversion efficiency of 20.73% under optimal water content conditions, and the unencapsulated devices maintained >83% of their initial efficiency after >1300 h in ambient air.

Over 20% Efficiency in Printable Mesoscopic Perovskite Solar Cells with Enhanced Open-Circuit Voltage via a Multifunctional Ionic Liquid

The large open-circuit voltage (VOC) losses limit the enhancement of power conversion efficiency (PCE) in printable mesoscopic perovskite solar cells (p-MPSCs). These losses primarily result from the high defect density at perovskite grain boundaries within the mesoporous scaffold, which promotes non-radiative recombination. In this study, the crystallization improvement and defect modulation of perovskite is promoted by adopting a multifunctional ionic liquid, 1-butyl-2,3-dimethylimidazolium trifluoromethanesulfonate (BMMIm[OTF]). The imidazolium ions in BMMIm[OTF] form hydrogen bonds with the PbI6 4- framework and coordinate with under-coordinated lead ions through S═O bonds. These interactions synergistically improve the crystallinity of perovskite films and optimize energy level alignment at the perovskite/carbon electrode interface. This improved interface facilitates more efficient charge transfer and extraction while reducing non-radiative recombination. As a result, the champion p-MPSCs incorporating BMMIm[OTF] achieve a PCE of 20.02% and a VOC of 1.055 V, significantly outperforming control devices with a VOC of 0.965 V. Furthermore, the hydrophobic nature of BMMIm[OTF] enhances device stability. This research provides a practical strategy for developing efficient and durable p-MPSCs.

A Brief Review of Perovskite Quantum Dot Solar Cells: Synthesis, Property and Defect Passivation

Perovskite quantum dot solar cells (PQDSCs), as the promising candidate for the next generation of solar cell, have garnered the significant attention over the past decades. However, the performance and stability of PQDSCs are highly dependent on the properties of interfaces between the perovskite quantum dots (PQDs) and the other layers in the device. This work provides a brief overview of PQDSCs, including the synthesis of PQDs, the characteristics and preparation methods of PQDs, the photoelectric properties as the light absorption layer and optimization methods for PQDSCs with high efficiency. Future directions and potential applications are also highlighted.

Strain Release via Glass Transition Temperature Regulation for Efficient and Stable Perovskite Solar Cells

Thermally induced tensile strain that remains in perovskite films after annealing is one of the key reasons for diminishing the performance and operational stability of perovskite solar cells (PSCs). Herein, a glass transition temperature (Tg) regulation (TR) strategy is developed by introducing two polymerizable monomers, 2-(N-3-Sulfopropyl-N,N-dimethyl ammonium)ethyl methacrylate (SBMA) and 2-Hydroxyethyl acrylate (HEA), into the perovskite layer. SBMA and HEA undergo in situ polymerization, which regulates the nucleation and crystal growth of the perovskite film. In addition, adjusting the ratio of SBMA and HEA to lower the Tg of the resulting polymer effectively releases the strain in the perovskite film. The modified film exhibits significantly reduced tensile strain, decreased trap density and improved stability. As a result, the optimized PSCs achieve a champion power conversion efficiency (PCE) of 26.15% (certified as 25.59%). Furthermore, the encapsulated device demonstrates prominent enhanced operation stability, maintaining 90.3% of its initial efficiency after 500 h of continuous sunlight exposure.

The Aging Chemistry of Perovskite Precursor Solutions

A significant barrier to the commercialization of solution-processed perovskite solar cells (PSCs) is the chemical instability of the components in precursor solutions under ambient conditions. This instability leads to solution aging, which subsequently diminishes the quality and reproducibility of the resulting PSCs. Inspired by recent published works, which focused on the deprotonation of organic cations, the oxidation of iodide, and the formation of undesired byproducts, we here systematically summarize and provide an outlook on the research directions and perspectives of the origin of precursor solution aging and countermeasures, such as using stabilizing additives, redox shuttles, Schiff base reactions, and green solvents. We are aiming to provide insight into potential paths for achieving reproducible and efficient PSCs with high operational stability.

Removal of Residual Additive Enabling Perfect Crystallization of Photovoltaic Perovskites

Achieving high-efficiency perovskite solar cells (PSCs) hinges on the precise control of the perovskite film crystallization process, often improved by the inclusion of additives. While dimethyl sulfoxide (DMSO) is traditionally used to manage this process, its removal from the films is problematic. In this work, methyl phenyl sulfoxide (MPSO) was employed instead of DMSO to slow the crystallization rate, as MPSO is more easily removed from the perovskite structure. The electron delocalization associated with the benzene ring in MPSO decreases the electron density around the oxygen atom in the sulfoxide group, thus reducing its interaction with PbI2. This strategy not only sustains the formation of a crystallization-slowing intermediate phase but also simplifies the elimination of the additive. Consequently, the optimized PSCs achieved a leading power conversion efficiency (PCE) of 25.95 % along with exceptional stability. This strategy provides a novel method for fine-tuning perovskite crystallization to enhance the overall performance of photovoltaic devices.

Dimensional engineering of interlayer for efficient large-area perovskite solar cells with high stability under ISOS-L-3 aging test

The utilization of low-dimensional perovskites (LDPs) as interlayers on three-dimensional (3D) perovskites has been regarded as an efficient strategy to enhance the performance of perovskite solar cells. Yet, the formation mechanism of LDPs and their impacts on the device performance remain elusive. Herein, we use dimensional engineering to facilitate the controllable growth of 1D and 2D structures on 3D perovskites. The differences of isomeric ligands in electrostatic potential distribution and steric effects for intermolecular forces contribute to different LDPs. The 1D structure facilitates charge transfer with favored channel orientation and energy level alignment. This approach enables perovskite solar modules (PSMs) using 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene to achieve an efficiency of 20.20% over 10 by 10 square centimeters (cm2) and 22.05% over 6 by 6 cm2. In particular, a PSM (6 by 6 cm2) using poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] maintains an initial efficiency of ~95% after 1000 hours under the rigorous ISOS-L-3 accelerated aging tests, marking a record for the highest stability of n-i-p structure modules.

Bridging-Solvent Strategy for Quasi-Single-Crystal Perovskite Films and Stable Solar Cells

Controllable fabrication of formamidinium (FA)-based perovskite solar cells (PSCs) with both high efficiency and long-term stability is the key to their further commercialization. However, the diversity of PbI2 complexes and perovskite compositions usually leads to light sensitive PbI2 residues and phase impurities in the film, which can accelerate the device degradation. Here, the crystallization kinetics of FA-based perovskite films are studied and a bridging-solvent strategy is proposed to modulate the reaction kinetics between PbI2 and ammonium salts by prohibiting the formation of undesired intermediates. N-methylpyrrolidone (NMP) solvent is introduced into the PbI2 precursor solution to obtain stable and homogeneous PbI2-NMP complex films. The strong interaction between NMP and formamidinium iodide (FAI) molecules promotes the conversion from PbI2-NMP into (001)-oriented quasi-single-crystal perovskite films with negligible impurities, long carrier lifetime of 1.5 µs and a large grain size of 3 µm. The optimized PSCs exhibit a high power conversion efficiency of 24.1%, as well as superior shelf stability which maintains 95% initial efficiency after storage in air for 1200 h (T95 = 1200 h), and operating stability with T96 = 300 h under continuous working at the maximum power point. This work offers a simple and reproducible method for fabricating phase-pure and uniaxially oriented perovskite films.

Dual Buried Interface Engineering for Improving Air-Processed Inverted FAPbI3 Perovskite Solar Cells

Fabricating perovskite solar cells (PSCs) in an ambient environment provides low-cost preparation routes for solar cells that are suitable for large-scale production. Compared with methylammonium (MA)- based perovskite materials, formamidinium lead iodide (FAPbI3) possesses a more favorable bandgap for light harvesting and better thermostability. However, the phase transition from the α-phase to the δ-phase easily occurs, making it challenging for ambient-air processing. Herein, we develop a buried interface engineering strategy via two molecules including 1,4-bis(diphenylphosphino)butane (DPPB) as well as [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl] phosphonic acid (Me-4PACz) to optimize air-processed inverted FAPbI3 PSCs. This strategy regulates the crystallization process of the air-fabricated FAPbI3 perovskite film, leading to a purer α-phase with significantly enhanced crystallinity and enlarged grain sizes. Apart from improving the bulk perovskite film, the defects at the NiOx/perovskite interface are passivated, and the energy levels are better matched in the modified device, which facilitates efficient carrier extraction. Resultantly, the target device processed in the open air achieves a dramatically improved power conversion efficiency from 11.37% to 18.45%, in association with an enhanced device stability.

Surface Reaction Induced Compressive Strain for Stable Inorganic Perovskite Solar Cells

Cesium-based inorganic perovskites have emerged as promising light-harvesting materials for perovskite solar cells (PSCs) due to their promising thermal- and photo-stability. However, obstacles to commercialization remain regarding their phase instability. In this work, we report a facile and effective strategy to regulate the surface compressive strain via in situ surface reaction to stabilize CsPbI3 perovskite. The use of a chelating ligand with a molecular configuration closely matching the integer multiples of the unit cell lattice parameters of CsPbI3 induces compressive strain at the surface of CsPbI3. The chemical bonding and strain modulation synergistically not only passivate film defects, but also inhibit perovskite phase degradation, thus significantly improving the intrinsic stability of inorganic perovskite. Consequently, enhanced power conversion efficiency (PCE) of 21.0 % and 18.6 % were respectively achieved in 0.16-cm2 lab-scale devices and 25.3-cm2 solar modules. Further, surface reaction enables PSCs with enhanced thermal and operational stability; these devices retain over 95 % of their initial PCE after damp-heat tests (i.e., in 85 °C and 85 % R. H. air) for 2000 h, and remain 99 % of their initial PCE after operating for 2000 h, representing one of the most stable inorganic PSCs reported so far.

Perovskite Crystallization Control for Large, Oriented Grains with Residual Solvent Restrain via Hydrogen-Bonded Organic Frameworks

Void-free perovskite films with oriented large grains are considered good performance. However, contradictory requirements on solvent volatilization arise that the growth of large grains requires slow volatilization while the residual solvent problem, which leads to difficult-handled voids at buried interface, requires quick and complete volatilization. Currently, although grain boundary additives help reach large and oriented grains, the occupation of additives in the grain boundary volatilization channel may further deteriorate the residual solvent problem. Herein, porous structures with "switchable pore" nature are constructed based on flexible hydrogen-bonded (HOF-FJU-2) in perovskite grain boundaries to meet both contradictory requirements with achieving crystallization control and residual solvent restrain. The additive molecules prolongs the perovskite crystallization through the Pb-O bond and guides the growth of (100) facet based on its strong ordered accumulation trend. The pre-embedded porous structure opens up the solvent volatilization channel for complete volatilization in annealing stage and then switches to a closed pore state via phase transformation after the solvent completely leaves, preventing the intrusion of the external environment. Combined with theoretical calculations and in situ spectrum tests, the crystallization thermodynamics and dynamics are analyzed. As expected, the target device exhibits enhanced performance (improved from 22.14% to 24.18%) and stability.

High-Temperature Driven Recrystallization for Stable Dopant-Free α-FAPbI3 Perovskite Solar Cells

High temperatures facilitate the formation of stable, high-crystallinity α-FAPbI3 films but can lead to the volatilization of organic components in perovskites. Here, a 300 °C hot-press-assisted recrystallization strategy is reported to grow stable phase-pure α-FAPbI3 film without any dopants. High temperature can promote the transformation of δ-FAPbI3 to α-FAPbI3, and induces recrystallization to relieve strain. The applied pressure creates a confined space that effectively prevents the volatilization of organic components in perovskite. The α-FAPbI3 film prepared by hot-press at 300 °C achieves an average grain size of ≈3 µm (with grains up to 10 µm) and demonstrates excellent damp-heat stability, showing no significant change after 20 s in deionized water. The result solar cell delivers a power conversion efficiency as high as 24.06% and retains >70% of their initial efficiency value after 1000 h at 85 °C and 85% relative humidity.

Recent progress of buried interface in high-efficiency and stable perovskite solar cells

Perovskite solar cells (PSCs) have been rapidly developed in recent years due to their excellent photovoltaic performance, which has been actively promoted by many researchers. However, interfacial non-radiative compounding hinders further improvement of their device performance. Buried interface modification strategies can minimize the non-radiative compounding within the interface, resulting in highly efficient and stable PSCs. In this review, we summarize the recent advances in the development of multiple classes of materials applied to buried interface engineering for the preparation of highly efficient and stable PSCs, including the development of organic, inorganic, and polymeric materials. The important role of buried interfaces in regulating energy alignment, passivating surface defects, modulating morphology, etc. have been discussed. Furthermore, we propose strategies to reduce nonradiative composites at interfaces. Finally, potential developments and challenges of buried interfaces for high performance stabilized PSCs are presented.

Micro-homogeneity of lateral energy landscapes governs the performance in perovskite solar cells

Suppression of energy disorders in the vertical direction of a photovoltaic device, along which charge carriers are forced to travel, has been extensively studied to reduce unproductive charge recombination and thus achieve high-efficiency perovskite solar cells. In contrast, energy disorders in the lateral direction of the junction for large-area modules are largely overlooked. Herein, we show that the micro-inhomogeneity characteristics in the surface lateral energetics of formamidinium (FA)-based perovskite films also significantly influence the device performance, particularly with accounting for the stability and scale-up aspects of the devices. By using organic amidinium passivators, instead of the most commonly used organic ammonium ones, the micro-inhomogeneity in the lateral energy landscapes can be suppressed, greatly improving device stability and efficiency of FA-based single-junction perovskite solar cells.

CO2 Laser Crystallization in Ambient for Highly Efficient FAPbI3 Perovskite Solar Cells

Metal halide perovskite solar cells have achieved tremendous progress and have attracted enormous research and development efforts since the first report of demonstration in 2009. Due to fabrication versatility, many heat treatment methods can be utilized to achieve perovskite film crystallization. Herein, 10.6 µm carbon dioxide laser process is successfully developed for the first time for perovskite film crystallization. In addition, this is the first time formamidinium lead triiodide solar cells by laser annealing under ambient are demonstrated. The champion cell produces a power conversion efficiency of 21.8%, the highest for laser-annealed perovskite cells. And this is achieved without any additive, passivation, or post-treatment.

Lattice Strain Regulation and Halogen Vacancies Passivation Enable High-Performance Formamidine-Based Perovskite Solar Cells

Formamidinium lead iodide (FAPbI3) perovskite has lately surfaced as the preferred contender for highly proficient and robust perovskite solar cells (PSCs), owing to its favorable bandgap and superior thermal stability. Nevertheless, volatilization and migration of iodide ions (I-) result in non-radiating recombination centers, and the presence of large formamidine (FA) cations tends to cause lattice strain, thereby reducing the power conversion efficiency (PCE) and stability of PSCs. To solve these problems, the lead formate (PbFa) is added into the perovskite solution, which effectively mitigates the halogen vacancy and provides tensile strain outside the perovskite lattice, thereby enhancing its properties. The strong coordination between the C═O of HCOO- and Pb-I backbones effectively immobilizes anions, significantly increases the energy barrier for anion vacancy formation and migration, and reduces the risk of lead ion (Pb2+) leakage, thereby improving the operation and environmental safety of the device. Consequently, the champion PCE of devices with Ag electrodes can be increased from 22.15% to 24.32%. The unencapsulated PSCs can still maintain 90% of the original PCE even be stored in an N2 atmosphere for 1440 h. Moreover, the target devices have significantly improved performance in terms of light exposure, heat, or humidity.

Confined Flash Printing and Synthesis of Stable Perovskite Nanofilms under Ambient Conditions

The fabrication of stable perovskite nanofilm patterns is important for the development of functional optical devices. However, current production approaches are limited by the requirement for strict inert gas protection and long processing times. Here, a confined flash printing synthesis method is presented to generate perovskite nanofilms under ambient conditions, combining precursor transfer, perovskite synthesis, crystallization, and polymer protection in a single step within milliseconds. A laser simultaneously prints and induces the flash synthesis, confined in a polymer nanofilm, under normal ambient conditions. Due to its simplicity and flexibility, the method enables the combination and screening of many different perovskite precursor materials on various substrates. Besides for the development of novel perovskite materials and devices, the nanofilms can be applied for biodetection. The unique H2O2-responsive property of the ultrathin perovskite quantum dot film is applied for biomolecule detection based on oxidase-catalyzed enzymatic reactions.

Br-Induced Suppression of Low-Temperature Phase Transitions in Mixed-Cation Mixed-Halide Perovskites

Mixed-cation mixed-halide lead perovskites have been shown to be excellent candidates for solar energy conversion. However, understanding the structural phases of these mixed-ion perovskites across a wide range of operating temperatures, including very low temperatures for space applications, is crucial. In this study, we investigated the structure of formamidinium-based Cs y FA1-y Pb(Br x I1-x )3 using low-temperature in situ synchrotron powder X-ray diffraction. Our findings revealed that substituting the I anion with Br in mixed-cation (Cs,FA) perovskites suppressed the phase transformation from tetragonal to orthorhombic at low temperatures. The addition of Br also prevented the formation of nonperovskite secondary phases. We gained fundamental insights into the structural behavior of these materials by creating a low-temperature phase diagram for the compositional set of mixed-cation mixed-halides. This understanding of the structural properties lays the groundwork for designing more robust and efficient energy materials capable of functioning under extreme temperature conditions, including space-based solar energy conversion.

The Promise and Challenges of Inverted Perovskite Solar Cells

Recently, there has been an extensive focus on inverted perovskite solar cells (PSCs) with a p-i-n architecture due to their attractive advantages, such as exceptional stability, high efficiency, low cost, low-temperature processing, and compatibility with tandem architectures, leading to a surge in their development. Single-junction and perovskite-silicon tandem solar cells (TSCs) with an inverted architecture have achieved certified PCEs of 26.15% and 33.9% respectively, showing great promise for commercial applications. To expedite real-world applications, it is crucial to investigate the key challenges for further performance enhancement. We first introduce representative methods, such as composition engineering, additive engineering, solvent engineering, processing engineering, innovation of charge transporting layers, and interface engineering, for fabricating high-efficiency and stable inverted PSCs. We then delve into the reasons behind the excellent stability of inverted PSCs. Subsequently, we review recent advances in TSCs with inverted PSCs, including perovskite-Si TSCs, all-perovskite TSCs, and perovskite-organic TSCs. To achieve final commercial deployment, we present efforts related to scaling up, harvesting indoor light, economic assessment, and reducing environmental impacts. Lastly, we discuss the potential and challenges of inverted PSCs in the future.

Enhanced charge carrier transport and defects mitigation of passivation layer for efficient perovskite solar cells

Surface passivation has been developed as an effective strategy to reduce trap-state density and suppress non-radiation recombination process in perovskite solar cells. However, passivation agents usually own poor conductivity and hold negative impact on the charge carrier transport in device. Here, we report a binary and synergistical post-treatment method by blending 4-tert-butyl-benzylammonium iodide with phenylpropylammonium iodide and spin-coating on perovskite surface to form passivation layer. The binary and synergistical post-treated films show enhanced crystallinity and improved molecular packing as well as better energy band alignment, benefiting for the hole extraction and transfer. Moreover, the surface defects are further passivated compared with unary passivation. Based on the strategy, a record-certified quasi-steady power conversion efficiency of 26.0% perovskite solar cells is achieved. The devices could maintain 81% of initial efficiency after 450 h maximum power point tracking.

Oxide Derivatives of Nb2CTx MXene and Their Application as Electron Transport Layers in Perovskite Solar Cells: Unraveling the Oxidation Process and Functionalization

In the realm of photovoltaic research, 2D transition metal carbides (MXenes) have gained significant interest due to their exceptional photoelectric capabilities. However, the instability of MXenes due to oxidation has a direct impact on their practical applications. In this work, the oxidation process of Nb2CTx MXene in aqueous systems is methodically simulated at the atomic level and nanosecond timescales, which elucidates the structural variations influenced by the synergistic effects of water and dissolved oxygen, predicting a transition from metal to semiconductor with 44% C atoms replaced by O atoms in Nb2CTx. Moreover, Nb2CTx with varying oxidation degrees is utilized as electron transport layers (ETLs) in perovskite solar cells (PSCs). Favorable energy level alignments with superior electron transfer capability are achieved by controlled oxidation. By further exploring the composites of Nb2CTx to its derivatives, the strong interaction of the nano-composites is demonstrated to be more effective for electron transport, thus the corresponding PSC achieves a better performance with long-term stability compared with the widely used ETLs like SnO2. This work unravels the oxidation dynamics of Nb2CTx and provides a promising approach to designing ETL by exploiting MXenes to their derivatives for photovoltaic technologies.

Solvent-Activated Transformation of Polymer Configurations for Advancing the Interfacial Reliability of Perovskite Photovoltaics

Organic materials have been widely used as the charge transport layers in perovskite solar cells due to their structural versatility and solution processability. However, their low surface energy usually causes unsatisfactory thin-film wettability in contact with the perovskite solution, which limits the interfacial performance of the photovoltaic devices. Although solvent post-treatment could occasionally regulate the wetting behavior of organic films, the mechanism of the solid-liquid interaction is still unclear. Here, we present evidence of a possible correlation between the solvent and the wettability of a conventional polymer, poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA), and reveal the critical roles of Hansen solubility parameters (HSPs) of solvents in wetting mechanisms. Our results suggest that the conventional solvent N,N-dimethylformamide (DMF) improves the wettability of PTAA by the morphological disruption mechanism but negatively impacts interfacial charge collection and stability. In contrast, 2-methoxyethanol (2-Me) with an appropriate HSP value induces the transformation of the PTAA configuration in an orderly manner, which simultaneously improves the wetting property and maintains the film topography. After careful optimization of the surface conformation of the PTAA film, both perovskite crystallization and interfacial compatibility have been enhanced. Benefiting from superior interfacial properties, the perovskite solar cells based on 2-Me deliver a champion efficiency of 24.15% compared to 21.4% for DMF-based ones. More encouragingly, the use of 2-Me minimizes the perovskite buried interfacial defects, enabling the unencapsulated devices to maintain about 95% of their initial efficiencies after light illumination for 1100 h. The present study demonstrates the high effectiveness of solvent-polymer interaction for adjusting interfacial properties and strengthening the robustness of perovskite solar cells.

Achievements, challenges, and future prospects for industrialization of perovskite solar cells

In just over a decade, certified single-junction perovskite solar cells (PSCs) boast an impressive power conversion efficiency (PCE) of 26.1%. Such outstanding performance makes it highly viable for further development. Here, we have meticulously outlined challenges that arose during the industrialization of PSCs and proposed their corresponding solutions based on extensive research. We discussed the main challenges in this field including technological limitations, multi-scenario applications, sustainable development, etc. Mature photovoltaic solutions provide the perovskite community with invaluable insights for overcoming the challenges of industrialization. In the upcoming stages of PSCs advancement, it has become evident that addressing the challenges concerning long-term stability and sustainability is paramount. In this manner, we can facilitate a more effective integration of PSCs into our daily lives.

Rational Strategies to Improve the Efficiency of 2D Perovskite Solar Cells

In the quest for durable photovoltaic devices, 2D halide perovskites have emerged as a focus of extensive research. However, the reduced dimension in structure is accompanied by inferior optical-electrical properties, such as widened band gap, enhanced exciton binding energy, and obstructed charge transport. As a result, the efficiency of 2D perovskite solar cells (PSCs) lags significantly behind their 3D counterparts. To overcome these constraints, extensive investigations into materials and processing techniques are pursued rigorously to augment the efficiency of 2D PSCs. Herein, The cutting-edge delve into developments in 2D PSCs, with a focus on chemical and material engineering, as well as their structure and photovoltaic properties. The review starts with an introduction of the crystal structure, followed by the key evaluation criteria of 2D PSCs. Then, the strategies around solution chemical engineering, processing technique, and interface optimization, to simultaneously boost efficiency and stability are systematically discussed. Finally, the challenges and perspectives associated with 2D perovskites to provide insights into potential improvements in photovoltaic performance will be outlined.

Lead-Chelating Intermediate for Air-Processed Phase-Pure FAPbI3 Perovskite Solar Cells

Formamidinium-lead triiodide (FAPbI3) perovskite holds promise as a prime candidate in the realm of perovskite photovoltaics. However, the photo-active α-FAPbI3 phase, existing as a metastable state, is observable solely at elevated temperatures and is susceptible to degradation into the δ-phase in ambient air. Therefore, the attainment of phase-stable α-FAPbI3 in ambient conditions has become a crucial objective in perovskite research. Here, we proposed an efficient conversion process of PbI2 into the α-FAPbI3 perovskites in ambient air. This conversion was facilitated by the introduction of chelating molecules, which interacted with PbI2 to form an intermediate phase. Due to the reduced formation barrier resulting from the altered reaction pathway, this stable intermediate phase transitioned directly into α-FAPbI3 upon the deposition of the organic cation solution, effectively bypassing the formation of δ-FAPbI3. Consequently, the ambient-fabricated FAPbI3 perovskite solar cells (PSCs) exhibited an outstanding power conversion efficiency of 25.08 %, along with a high open-circuit voltage of 1.19 V. Furthermore, the unencapsulated devices demonstrated remarkable environmental stability. Notably, this innovative approach promises broad applicability across various chelating molecules, opening new avenues for further progress in the ambient air fabrication of FAPbI3 PSCs.

Two-Step Perovskite Solar Cells with > 25% Efficiency: Unveiling the Hidden Bottom Surface of Perovskite Layer

While significant efforts in surface engineering have been devoted to the conversion process of lead iodide (PbI2) into perovskite and top surface engineering of perovskite layer with remarkable progress, the exploration of residual PbI2 clusters and the hidden bottom surface on perovskite layer have been limited. In this work, a new strategy involving 1-butyl-3-methylimidazolium acetate (BMIMAc) ionic liquid (IL) additives is developed and it is found that both the cations and the anions in ILs can interact with the perovskite components, thereby regulating the crystallization process and diminishing the residue PbI2 clusters as well as filling vacancies. The introduction of BMIMAc ILs induces the formation of a uniform porous PbI2 film, facilitating better penetration of the second-step organic salt and fostering a more extensive interaction between PbI2 and the organic salt. Surprisingly, the oversized residual PbI2 clusters at the bottom surface of the perovskite layer completely diminish. In addition, advanced depth analysis techniques including depth-resolved grazing-incidence wide-angle X-ray scattering (GIWAXS) and bottom thinning technology are employed for a comprehensive understanding of the reduction in residual PbI2. Leveraging effective PbI2 management and regulation of the perovskite crystallization process, the champion devices achieve a power conversion efficiency (PCE) of 25.06% with long-term stability.

Controlled Nucleation and Oriented Crystallization of Methylammonium-Free Perovskites via In Situ Generated 2D Perovskite Phases

Enhancing stability while maintaining high efficiency is among the primary challenges in the commercialization of perovskite solar cells (PSCs). Here, a crystal growth technique assisted by in situ generated 2D perovskite phases has been developed to construct high-quality 2D/3D perovskite films. The in situ generated 2D perovskite serve as templates for regulating the nucleation and oriented crystal growth in the α-FAPbI3-rich film. This led to a high film quality with much reduced trap density and an ultralong carrier lifetime. The obtained perovskite film shows excellent stability under extreme environment conditions (T = 200 °C, RH = 75 ± 5%). The corresponding PSC achieved an efficiency of 26.16% (certified 25.84%), along with excellent operational stability (T93 > 1300 h, T ≅ 50 °C) as well as outstanding high and low temperature cycle stability.

A crystal capping layer for formation of black-phase FAPbI3 perovskite in humid air

Black-phase formamidinium lead iodide (α-FAPbI3) perovskites are the desired phase for photovoltaic applications, but water can trigger formation of photoinactive impurity phases such as δ-FAPbI3. We show that the classic solvent system for perovskite fabrication exacerbates this reproducibility challenge. The conventional coordinative solvent dimethyl sulfoxide (DMSO) promoted δ-FAPbI3 formation under high relative humidity (RH) conditions because of its hygroscopic nature. We introduced chlorine-containing organic molecules to form a capping layer that blocked moisture penetration while preserving DMSO-based complexes to regulate crystal growth. We report power conversion efficiencies of >24.5% for perovskite solar cells fabricated across an RH range of 20 to 60%, and 23.4% at 80% RH. The unencapsulated device retained 96% of its initial performance in air (with 40 to 60% RH) after 500-hour maximum power point operation.

Ultrastable and efficient slight-interlayer-displacement 2D Dion-Jacobson perovskite solar cells

Stability has been a long-standing concern for solution-processed perovskite photovoltaics and their practical applications. However, stable perovskite materials for photovoltaic remain insufficient to date. Here we demonstrate a series of ultrastable Dion-Jacobson (DJ) perovskites (1,4-cyclohexanedimethanammonium)(methylammonium)n-1PbnI3n+1 (n ≥ 1) for photovoltaic applications. The scalable technology by blade-coated solar cells for the designed DJ perovskites (nominal n = 5) achieves a maximum stabilized power conversion efficiency (PCE) of 19.11% under an environmental atmosphere. Un-encapsulated cells by blade-coated technology retain 92% of their initial efficiencies for over 4000 hours under ~90% relative humidity (RH) aging conditions. More importantly, these cells also exhibit remarkable thermal (85 °C) and operational stability, which shows negligible efficiency loss after exceeding 5000-hour heat treatment or after operation at maximum power point (MPP) exceeding 6000 hours at 45 °C under a 100 mW cm-2 continuous light illumination.

Ecofriendly Solution Processing of Perovskite Solar Cells Using Water

Perovskite solar cells (PSCs) represent a promising avenue for producing cost-effective solar energy by harnessing sunlight, but challenges persist in their solution processing, which uses a large amount of organic solvent for existing PSC technology. The use of water as a solvent offers an environmentally friendly alternative to traditional solvents, aligning with the global drive for sustainable renewable energy technologies. This Perspective provides an overview of research in the area of PSC fabrication using water as a solvent, highlighting key advancements in the synthesis process. We delve into the kinetics of crystallization and the physical-chemical transformations of perovskite materials in water-based solution processing. Key challenges of the scalability of water-based solution processing for PSC fabrication are discussed. The Perspective sheds light on the broader potential for enhancing the ecofriendliness of perovskite solar cell technologies.

Degassing 4-tert-Butylpyridine in the Spiro-MeOTAD Film Improves the Thermal Stability of Perovskite Solar Cells

The organic molecular 2,2',7,7'-tetrakis(4,4'-dimethoxy-3-methyldiphenylamino)-9,9'-spirobifluorene (Spiro-MeOTAD) is known as a typical hole transport material in the development of an all-solid-state perovskite solar cell (PSC). Spiro-MeOTAD requires additives of lithium bifurflimide (LiTFSI) and 4-tert-butylpyridine (tBP) to increase the conductivity and solubility for enhancing the photovoltaic performance of PSCs. However, those additives have an adverse effect on the thermal stability. We report on the origin of instability of additive-containing Spiro-MeOTAD at 85 °C and the methodology to solve the thermal instability. We have found that the interaction of LiTFSI with the underneath perovskite surface facilitated by diffusive tBP is responsible for thermal degradation. Degasification of tBP from the Spiro-MeOTAD film is found to be the key to achieving thermally stable PSCs, where the optimal degassing process achieves 90% of the initial power conversion efficiency (PCE) at 85 °C after 1000 h.

Polyfluorinated Organic Diammonium Induced Lead Iodide Arrangement for Efficient Two-Step-Processed Perovskite Solar Cells

The inefficient conversion of lead iodide to perovskite has become one of the major challenges in further improving the performance of perovskite solar cells fabricated by the two-step method. Herein, the discontinuous lead iodide layer realized by introduction of a polyfluorinated organic diammonium salt, octafluoro-([1,1'-biphenyl]-4,4'-diyl)-dimethanaminium (OFPP) iodide which does not form low-dimensional perovskites, can enable the satisfactory conversion of lead iodide into perovskite, leading to meliorated crystallinity and enlarged grains in the OFPP modulated perovskite (OFPP-PVK) film. Combined with the effective defect passivation, the OFPP-PVK films show enhanced charge mobility and suppressed charge recombination. Accordingly, the OFPP-based perovskite solar cells exhibit a champion efficiency of 24.76 % with better device stability. Moreover, a superior efficiency of 21.04 % was achieved in a large-area perovskite module (100 cm2). Our work provides a unique insight into the function of organic diammonium additive in boosting photovoltaic performance.

Efficient Air-Processed MA-Free Perovskite Solar Cells by SH-Based Silane Interface Modification

Air-processed perovskite solar cells (PSCs) with high photoelectric conversion efficiency (PCE) can not only further reduce the production cost but also promote its industrialization. During the preparation of the PSCs in ambient air, the contact of the buried interface not only affects the crystallization of the perovskite film but also affects the interface carrier transport, which is directly related to the performance of the device. Here, we optimize the buried interface by introducing 3-mercaptopropyltrimethoxysilane (MPTMS, (CH3O)3Si(CH2)3SH) on the nickel oxide (NiOx) surface. The crystallization of the perovskite film is improved by enhancing surface hydrophobicity; besides, the SH-based functional group of MPTMS passivates the uncoordinated lead at the interface, which effectively reduces the defects at the bottom interface of perovskite and inhibits the nonradiative recombination at the interface. Moreover, the energy level between the NiOx layer and the perovskite layer is better matched. Based on multiple functions of MPTMS modification, the open circuit voltage of the device is obviously improved, and efficient air-processed methylamine-free (MA-free) PSCs are realized with PCE reaching 21.0%. The device still maintains the initial PCE of 85% after 1000 h aging in the glovebox. This work highlights interface modification in air-processed MA-free PSCs to promote the industrialization of PSCs.