Silver bismuth iodide (SBI) materials have recently gained attention as nontoxic alternatives to lead perovskites. Although most of the studies have been focusing on photovoltaic performance, the inherent ionic nature of SBI materials, their diffusive behavior, and influence on material/device stability is underexplored. Herein, AgBi2I7, Ag2BiI5, and Ag3BiI6 thin films are developed in controlled ambient humidity conditions with a decent efficiency up to 2.32%. While exploring the device stability, it is found that Ag3BiI6 exhibits a unique ion‐migration behavior where Ag+, Bi3+, and I− ions migrate and diffuse through the dopant‐free hole transport layer (HTL) leading to degradation. Interestingly, this ion‐migration behavior is relatively fast for the case of antisolvent‐processed Ag3BiI6 thin‐film‐based devices contrasting the case of without antisolvent and is not observed for other SBI material‐based devices. Theoretical calculations suggest that low decomposition enthalpy favors the decomposition of Ag3BiI6 to AgI and BiI3 causing migration of ions to the electrode which is protected by using a thick HTL . The new mechanism reported herein underlines the importance of SBI material composition and fundamental mechanism understanding on the stability of Ag3BiI6 material for better solar cell design and also in extending the applications of unique ion‐migration behavior in various optoelectronics.

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Investigation of the perovskite (MAPbI3; MA+ = CH3NH3 +) crystallization, location of residual lead iodide (PbI2), and its influence on the optoelectronic and photovoltaic properties is important to resolve the low-efficiency issue in radio frequency (RF) sputtered nickel oxide (sp-NiO x ) based perovskite solar cells (PSCs). Despite obtaining the perovskite layer from a solution of the stoichiometric ratio of precursor materials using a one-step method (OSM) for spin-coating, residual PbI2 grains are observed (from the top surface scanning electron microscopy (SEM) image) in the bulk of perovskite (deposited on sp-NiO x ). To investigate the dependence of residual PbI2 on the preparation methods, we prepared the perovskite (on sp-NiO x ) by a two-step method (TSM) in which methylammonium iodide (MAI) solution is spin-coated on top of the deposited PbI2 layer. The cross-sectional SEM image of the TSM-based perovskite device, confirms the presence of the residual PbI2 layer (20–50 nm) at the interface of perovskite/NiO x . Although a higher X-ray diffraction (XRD) peak intensity of residual PbI2 was observed, the higher crystallinity of the perovskite film prepared by TSM was confirmed based on the evaluation of the photoluminescence (PL) peaks and the PL lifetime. In comparison with the devices prepared by OSM, the higher photovoltaic performance of PSCs is observed for devices fabricated using TSM. An investigation on the relation of the device performance with the location of residual PbI2 is presented in this work and can be insightful to further improve the performance of sp-NiO x -based PSCs.