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Abstract: The phase instability and large energy loss are two obstacles to achieve stable and efficient inorganic‐CsPbI3−xBrx perovskite solar cells. In this work, stable cubic perovskite (α)‐phase CsPbI2Br is successfully achieved by Pb(Ac)2 functioning at the grain boundary under low temperature. Ac− strongly coordinates with CsPbI2Br to stabilize the α‐phase and also make the grain size smaller and film uniform by fast nucleation. PbO is formed in situ at the grain boundary by decomposing Pb(Ac)2 at high‐temperature annealing. The semiconducting PbO effectively passivates the surface states, reduces the interface recombination, and promotes the charge transport in CsPbI2Br perovskite solar cells. A 12% efficiency and good stability are obtained for in situ PbO‐passivated CsPbI2Br solar cells, while Pb(Ac)2‐passivated device exhibits 8.7% performance and the highest stability, much better than the control device with 8.5% performance and inferior stability. This article highlights the extrinsic ionic grain boundary functionalization to achieve stable and efficient inorganic CsPbI3−xBrx materials and the devices. [ABSTRACT FROM AUTHOR]

Abstract: Ionic movement is considered awful in perovskite solar cells (PSCs) for relating with the hysteresis and long‐term instability. However, the positive role of ions to enhance the energy band bending for high performance PSC is always overlooked, let alone reducing the hysteresis. In this work, LiI is doped in CH3NH3PbI3. It is observed that the aggregation of Li+/I− tunes the energy level of the perovskite and induces n/p doping in CH3NH3PbI3, which makes charge extraction quite efficient from perovskite to both NiO and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) layer. Therefore, in NiO/LiI doped perovskite/PCBM solar cells, Li+ and I− modulate the interface energy band alignment to facilitate the electron/hole transport and reduce the interface energy loss. On the other hand, n/p doping enlarges Fermi energy level splitting of the PSCs to improve the photovoltage. The performance of LiI doped PSCs is much higher with reduced hysteresis compared to the undoped solar cells. This work highlights the positive effect of selective ionic doping, which is promisingly important to design the stable and efficient PSCs. [ABSTRACT FROM AUTHOR]

Fabrication of efficient Pb reduced inorganic CsPbI2Br perovskite solar cells (PSC) are an important part of environment‐friendly perovskite technology. In this work, 10% Pb reduction in CsPb0.9Zn0.1I2Br promotes the efficiency of PSCs to 13.6% (AM1.5, 1sun), much higher than the 11.8% of the pure CsPbI2Br solar cell. Zn2+ has stronger interaction with the anions to manipulate crystal growth, resulting in size‐enlarged crystallite with enhanced growth orientation. Moreover, the grain boundaries (GBs) are passivated by the Cs‐Zn‐I/Br compound. The high quality CsPb0.9Zn0.1I2Br greatly diminishes the GB trap states and facilitates the charge transport. Furthermore, the Zn4s‐I5p states slightly reduce the energy bandgap, accounting for the wider solar spectrum absorption. Both the crystalline morphology and energy state change benefit the device performance. This work highlights a nontoxic and stable Pb reduction method to achieve efficient inorganic PSCs. [ABSTRACT FROM AUTHOR]