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Formamidinium lead triiodide (FAPbI3 ) is attractive for photovoltaic devices due to its optimal bandgap at around 1.45 eV and improved thermal stability compared with methylammonium-based perovskites. Crystallization of phase-pure α-FAPbI3 conventionally requires high-temperature thermal annealing at 150 °C whilst the obtained α-FAPbI3 is metastable at room temperature. Here, aerosol-assisted crystallization (AAC) is reported, which converts yellow δ-FAPbI3 into black α-FAPbI3 at only 100 °C using precursor solutions containing only lead iodide and formamidinium iodide with no chemical additives. The obtained α-FAPbI3 exhibits remarkably enhanced stability compared to the 150 °C annealed counterparts, in combination with improvements in film crystallinity and photoluminescence yield. Using X-ray diffraction, X-ray scattering, and density functional theory simulation, it is identified that relaxation of residual tensile strains, achieved through the lower annealing temperature and post-crystallization crystal growth during AAC, is the key factor that facilitates the formation of phase-stable α-FAPbI3 . This overcomes the strain-induced lattice expansion that is known to cause the metastability of α-FAPbI3 . Accordingly, pure FAPbI3 p-i-n solar cells are reported, facilitated by the low-temperature (≤100 °C) AAC processing, which demonstrates increases of both power conversion efficiency and operational stability compared to devices fabricated using 150 °C annealed films.

Fullerene derivatives are widely employed as efficient electron-transporting layers (ETLs) in p-i-n perovskite photovoltaics but face challenges in mitigating interfacial recombination losses and ensuring stable film morphology. Non-fullerene acceptors (NFAs), commonly utilized in organic photovoltaics, present a promising alternative to fullerene-based ETLs. Nevertheless, the suboptimal performance of NFA-based devices underscores the need for molecular engineering to tailor their properties. Herein, we develop two Y-type NFAs, Y-Phen and Y-CE, by substituting the benzothiadiazole core of Y6 with higher-polarity phenanthroline and crown ether. These modifications effectively enhance carrier kinetics by (1) promoting ordered molecular assembly on the perovskite surface through supramolecular interactions, thereby optimizing interfacial energetic alignment, and (2) improving the molecular packing to facilitate efficient charge transport. Using Y-CE as the ETL, the device achieves a certified power conversion efficiency (PCE) of 25.59%. Furthermore, the optimized device exhibits less than 10% degradation in PCE after 1440 hours of thermal aging. This work offers valuable insights into designing NFA-based ETLs for high-performance perovskite photovoltaics. The suboptimal performance of perovskite solar cells based on non-fullerene acceptor as the electron-transporting layer underscores the need for their molecular engineering. Here, authors substitute the core of Y6 with phenanthroline and crown ether, achieving a certified efficiency of 25.59%. [ABSTRACT FROM AUTHOR]

The inherent defects (lead iodide inversion and iodine vacancy) in perovskites cause non‐radiative recombination and there is also ion migration, decreasing the efficiency and stability of perovskite devices. Eliminating these inherent defects is critical for achieving high‐efficiency perovskite solar cells. Herein, an organic molecule with multiple active sites (4,7‐bromo‐5,6‐fluoro‐2,1,3‐phenylpropyl thiadiazole, M4) is introduced to modify the upper interface of perovskites. When M4 interacts with the perovskite surface, the active bromine (Br) site interacts with lead (Pb) at the surface to repair iodine atomic vacancy defects. The fluorine (F) site of M4 interacts with Pb to correct octahedral crystal lattice distortions and eliminate PbI defects. Additionally, sulfur–iodine (S–I) interactions reduce I–I dimerization and eliminate IPb defects. It is also calculated that the energy level of M4 aligns with the band gap, promoting charge transfer. As a result, the perovskite devices achieve an efficiency of 25.1%, a stabilized power output (SPO) of 25.0%, a voltage of 1.19 V, and a fill factor of 85.2%. The device retains 95% of its initial efficiency after 2000 h of ageing in a nitrogen atmosphere. Thus, multi‐point cooperative passivation of surface defects provides an effective method to improve the efficiency and stability of perovskite solar cells. [ABSTRACT FROM AUTHOR]

All‐inorganic cesium lead halide flexible perovskite solar cells (f‐PSCs) exhibit superior thermal stability compared to their organic‐inorganic hybrid counterparts. However, their flexibility and efficiency are still below‐par for practical viability. This study presents an approach involving the introduction of multifunctional molecule ammonium benzenesulfonate (ABS) to selectively etch 0D‐Cs4Pb(IBr)6 from the mixed‐dimensional perovskite film surface, to attain more contact area between the perovskite and hole transport layer for improved hole extraction and transport. It is found that the ABS molecules bind to the perovskite lattice surface via O atoms and NH4+, effectively passivating surface defects and enhancing phase stability. The hydrophobic nature of the benzene ring in ABS further contributes to operational stability, leading to high cell efficiency of 15.00%, accompanied by enhanced operational stability. Even after undergoing 60 000 flexing cycles at a curvature radius of 5 mm, the ABS‐treated f‐PSC still retains over 98.5% of its initial efficiency. This multifunctional strategy for modifying typical mixed‐dimensional perovskite compositions significantly enhances the photovoltaic performance and stability of flexible all‐inorganic f‐PSCs. [ABSTRACT FROM AUTHOR]

Mixed tin‐lead perovskite solar cells can reach band gaps as low as 1.2 eV, offering high theoretical efficiency and serving as base materials for all‐perovskite tandem solar cells. However, instability and high defect densities at the interfaces, particularly the buried surface, have limited performance improvements. In this work, we present the modification of the bottom perovskite interface with multifunctional hydroxylamine salts. These salts can effectively coordinate the different perovskite components, having critical influences in regulating the crystallization process and passivating defects of varying nature. The surface modification reduced traps at the interface and prevented the formation of excessive lead iodide, enhancing the quality of the films. The modified devices presented fill factors reaching 81 % and efficiencies of up to 23.8 %. The unencapsulated modified devices maintained over 95 % of their initial efficiency after 2000 h of shelf storage. [ABSTRACT FROM AUTHOR]

Phase segregation can bring low crystallinity and orientation, giving rise to poor carrier transport and high defect density, leading to poor device performance. In order to reduce oxidation and defect density and regulate film growth, lots of reductive additives such as SnF2 are explored as additives in tin perovskite film growth. Despite the oxidation is effectively reduced, it induces phase segregation. Herein, a reductive molecule NH5F2 with a bi‐fluoride anion is explored to address this challenge for tin perovskite solar cells. This bi‐fluoride anion reduces coordination energy with Sn2+ compared to SnF2, hence the byproduct of [F─H─F]− can be eliminated during the film annealing process, effectively preventing fluoride segregation. As a result, a highly oriented perovskite film with reduced oxidation is fabricated. The film shows reduced defect density and carrier recombination, leading to improved current density. Consequently, a tin‐based perovskite solar cell with an efficiency of 15.04% is fabricated, ranking as one of the highest efficiencies reported up to now. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Metal halide perovskite wafers have shown significant potential in large‐area X‐ray detection and imaging. However, a distinct difference in optical transparency between state‐of‐the‐art perovskite wafers and single crystals indicates the inferior crystal quality of perovskite wafers, which limits the performance and stability of wafer‐based X‐ray detectors. Here, nano‐sized MAPbBr3 powders are utilized to fabricate dense perovskite wafers by low‐temperature hot‐pressing with high transparency above 60% within the 552–800 nm wavelength range. Adjacent nanocrystals assemble following the ordered coalescence mechanism, resulting in the exclusion of nanoscopic pores and crystallographic reorientation. The transparent MAPbBr3 wafer‐based detectors achieve an impressively high X‐ray sensitivity of 1.14 × 105 µC Gyair−1 cm−2 and a low detection limit of 149 nGyair s−1, which is superior to opaque MAPbBr3 wafer detectors (5.64 × 104 µC Gyair−1 cm−2 and 316.7 nGyair s−1) and comparable to MAPbBr3 single‐crystal detectors. Moreover, the detectors demonstrate high uniformity and outstanding stability under continuous X‐ray irradiation of a total dose of up to 5.9 Gyair, equaling to 29 500 times posteroanterior chest examinations. The high sensitivity and low detection limit of the detectors lead to clear X‐ray imaging performance. [ABSTRACT FROM AUTHOR]

Two‐step sequential deposition of perovskite films is proven efficient and compatible with large‐scale production. Nevertheless, its critically regulated environmental humidity often remains a burden, hindering its applications in reproducible fabrication of perovskite solar cells (PSCs). Herein, by introducing a water ethyl acetate (W‐EA) solution treatment before annealing, improved perovskite crystallinity and homogeneity in FA0.95‐xMAxCs0.05PbI3 films without additional composition regulation is achieved. In situ Grazing‐incidence Wide‐angle X‐ray Scattering experiments highlighted accelerated crystallization kinetics in W‐EA‐treated films, leading to high‐quality perovskite formation. PSCs based on this method reached an optimal power conversion efficiency of 25.01% and demonstrated enhanced moisture resistance, retaining 88% efficiency after 1000 h in ambient conditions. This W‐EA treatment simplifies the fabrication process, greatly reducing the need for controlled humidity, and offers insights into the role of water in perovskite film crystallization, with significant implications to produce high‐performance PSCs. [ABSTRACT FROM AUTHOR]

Two‐dimensional materials have been widely used to tune the growth and energy‐level alignment of perovskites. However, their incomplete passivation and chaotic usage amounts are not conducive to the preparation of high‐quality perovskite films. Herein, we succeeded in obtaining higher‐quality CsPbBr3 films by introducing large‐area monolayer graphene as a stable physical overlay on top of TiO2 substrates. Benefiting from the inert and atomic smooth graphene surface, the CsPbBr3 film grown on top by the van der Waal epitaxy has higher crystallinity, improved (100) orientation, and an average domain size of up to 1.22 μm. Meanwhile, a strong downward band bending is observed at the graphene/perovskite interface, improving the electron extraction to the electron transport layers (ETL). As a result, perovskite film grown on graphene has lower photoluminescence (PL) intensity, shorter carrier lifetime, and fewer defects. Finally, a photovoltaic device based on epitaxy CsPbBr3 film is fabricated, exhibiting power conversion efficiency (PCE) of up to 10.64% and stability over 2000 h in the air. [ABSTRACT FROM AUTHOR]

BackgroundAll-inorganic perovskite solar cells have been extensively studied for their phase and thermal stability. In perovskite solar cells, the interface energy level arrangement between the hole transport layer (HTL) and the perovskite layer plays a decisive role in the performance of the device. Suitable interfacial energy level alignment is essential to facilitate the injection of photogenerated holes from perovskite into the HTL simultaneously effectively block electron transport efficiently, thus suppressing the recombination of holes with electrons.PurposeThis study aims to precisely determine the interfacial energy level alignment between CsPbI2Br and Spiro-OMeTAD experimentally.MethodsFirst of all, the Spiro-OMeTAD was deposited on CsPbI2Br film, then the interfacial electronic structure between CsPbI2Br and Spiro-OMeTAD was investigated by in situ X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. Finally, the fabricated CsPbI2Br film was characterized by synchrotron-based grazing incidence X-ray diffraction (GIXRD) and scanning electron microscope (SEM).ResultsExperimental results show that there is no detectable interaction observed at the Spiro-OMeTAD/CsPbI2Br interface where electrons accumulate due to the formed interfacial state. An interfacial dipole of 0.18 eV is formed at the interface with 0.13 eV and 0.27 eV upward energy band bending at the CsPbI2Br substrate side and the Spiro-OMeTAD side, respectively. The hole injection barrier at the interface as indicated by the gap between the CsPbI2Br valence band maximum (VBM) and the Spiro-OMeTAD highest occupied molecular orbital (HOMO) is determined to be 0.23 eV, which favours the hole injection and extraction. Meanwhile, the gap between the CsPbI2Br conduction band minimum (CBM) to the Spiro-OMeTAD lowest unoccupied molecular orbital (LUMO) known as the electron-blocking barrier is up to 1.25 eV, effectively blocking the electron transfer from CsPbI2Br to Spiro-OMeTAD with the interfacial recombination efficiently suppressed.ConclusionsIt is concluded that Spiro-OMeTAD is an excellent HTL material in CsPbI2Br-based all-inorganic perovskite solar cells. The present work also provides meaningful guidance for the tunning interfacial electronic structure between perovskite and HTLs for high-performance CsPbI2Br solar cells.