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The inorganic perovskite solar cells (IPSC) are promising in the context of simultaneously delivering high efficiency and good stability. Developing a high‐performance and larger band gap IPSC is particularly in demand for commercialization due to their suitability to match with the prevailing silicon solar cells for tandem devices, while this is hindered by the poor morphology and phase stability of inorganic perovskite films. To address this issue, this work develops a combined method of nonstoichiometric composition and post‐cation exchange to improve the morphology and phase stability of the CsPbI2Br IPSCs, and achieves a record efficiency of 17.80%. This work finds that excessive PbI2 regulates the CsPbI2Br film crystallization, and thus, a high‐quality perovskite film with enlarged grains is obtained. Further depositing the formamidinium iodide on top of the CsPbI2Br perovskite induces cation exchange during the post‐annealing process, which increases the phase stability of the perovskite film and significantly improves the device efficiency and stability. Therefore, this work provides an avenue toward high‐performance IPSCs, via the nonstoichiometric and ion exchange method. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: The surface properties and chemical interactions are critical for perovskite solar cells (PVSCs). In this work, we show that the polypropylene glycol (PPG) can simultaneously passivate the NiOx surface and grain boundaries of perovskite films, allowing more efficient charge transfer at the anode interface and reducing the recombination of PVSCs. As a result, the open‐circuit voltage (Voc) of MAPbI3 based inverted PVSCs increases from 1.087 V to 1.127 V, and the short‐circuit current density (Jsc) is increased from 20.87 mA·cm–2 to 22.32 mA·cm–2, thereby realizing the improvement of the device power conversion efficiency (PCE) from 18.34% to 20.12%. Moreover, the steady‐state output of the PVSCs is remarkably improved by incorporating PPG. Further analysis of surface properties suggests that part of the PPG at the interface can permeate into the precursor solution with the help of DMF solvent and remain in the perovskite layer to form a concentration gradient. The ether bond of PPG and the uncoordinated Pb2+ in the perovskite are coordinated to achieve passivation effects and improve device performance. Our work provides a rational strategy for the preparation of high‐performance PVSCs. [ABSTRACT FROM AUTHOR]

Controlling the crystallization of perovskite film is critical for high‐performance perovskite solar cells (PVSCs), and temperature is the key factor dominating the nucleation and crystal growth. Herein, it is demonstrated that the inconspicuous ambient temperature plays an important role in reaching high‐quality perovskite film and high‐performance PVSCs. It is observed that the ambient temperature greatly affects the composition of as‐prepared perovskite film, which dramatically influences the perovskite film morphology during the subsequent annealing process. Remarkably, the device prepared at the optimal ambient temperature of 29 °C exhibits the best power conversion efficiency of 20.91% with little hysteresis. This represents one of the best results for inverted PVSCs based on pristine MAPbI3 system. In addition, the PVSC prepared at 29 °C shows good stability with 80% of its initial efficiency after 30d in air with a humidity of 45%. Overall, the importance of ambient temperature for crystallization of the perovskite film is emphasized, and this work should have implications for controlling the morphology for high‐performance PVSCs. [ABSTRACT FROM AUTHOR]

Surface or interface engineering is one of the most effective strategies to improve the device performance and stability of perovskite solar cells (PSCs), owing to the fact that the defects are mainly located at the surface. Organosilanes are among the most promising surface modifiers due to their unique cross‐linking ability, which makes a robust layer to further protect the underneath perovskites. However, the influence of tail functional groups of organosilanes on the device performance and stability has never been systematically investigated. Herein, a series of organosilanes with different chain lengths, fluorination, and different interactions toward perovskite are applied to modify the perovskite. Tail functional groups that show passivation ability toward perovskite are demonstrated to effectively reduce trap densities and thus improve the power conversion efficiencies (PCEs), while the fluorinated functional groups are beneficial for high stability. Finally, PSCs based on 3,3,3‐trifluoropropyltrimethoxysilane (FPTMS) modification showed a high PCE of 23.0% with the best operational stability. The encapsulated device maintained 85% of the initial PCE after 1725 h under continuous 1 sun equivalent illumination in air. The work may provide important insights into designing modifiers for high‐performance PSCs with high stability. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: The surface properties and chemical interactions are critical for perovskite solar cells (PVSCs). In this work, we show that the polypropylene glycol (PPG) can simultaneously passivate the NiOx surface and grain boundaries of perovskite films, allowing more efficient charge transfer at the anode interface and reducing the recombination of PVSCs. As a result, the open‐circuit voltage (Voc) of MAPbI3 based inverted PVSCs increases from 1.087 V to 1.127 V, and the short‐circuit current density (Jsc) is increased from 20.87 mA·cm–2 to 22.32 mA·cm–2, thereby realizing the improvement of the device power conversion efficiency (PCE) from 18.34% to 20.12%. Moreover, the steady‐state output of the PVSCs is remarkably improved by incorporating PPG. Further analysis of surface properties suggests that part of the PPG at the interface can permeate into the precursor solution with the help of DMF solvent and remain in the perovskite layer to form a concentration gradient. The ether bond of PPG and the uncoordinated Pb2+ in the perovskite are coordinated to achieve passivation effects and improve device performance. Our work provides a rational strategy for the preparation of high‐performance PVSCs. [ABSTRACT FROM AUTHOR]

Inverted-structure perovskite solar cells (PVSCs) applying NiO x as the hole transport layer (HTL) have attracted increasing attention. It is still a challenge to optimize the contact between NiO x and the perovskite layer and to suppress energy loss at the interface. In this study, interface engineering was carried out by modifying the NiO x layer with different polymers such as polystyrene, poly(methyl methacrylate) (PMMA), or poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) to improve the surface contact between NiO x and the perovskite, to decrease the defect states, and to make the energy level alignment better. The NiO x /PMMA-based device presents a V oc as high as 1.19 V because of the improved interfacial contact and the interaction of the carbonyl and methoxy group with Pb 2+ . The NiO x /PTAA-based device with the structure ITO/NiO x /PTAA/(MAPbI 3 ) 0.95 (MAPbBr 2 Cl) 0.05 /PCBM/BCP/Ag exhibits the highest power conversion efficiency of 21.56% with a high V oc of 1.19 V. The enhanced performance can be attributed to the deepened highest occupied molecular orbital level of NiO x /PTAA, which matched well with that of the perovskite and suppressed interface energy loss as well. This work provides a facile approach for efficiently improving the V oc of NiO x -based PVSCs.