Low-temperature processing of polyvinylpyrrolidone modified CsPbI₂Br perovskite films for high-performance solar cells

Owing to the inevitability of moisture/thermal instability in organic-inorganic hybrid perovskites, pure inorganic perovskites such as CsPbI₂Br perovskite have surfaced as promising options for commercial perovskite solar cells (PSCs) due to their high photovoltaic performance and excellent inherent stability. However, designing additive engineering approaches to mitigate defect-induced crystalline phase transitions from a photosensitive perovskite phase to a non-perovskite phase has been a difficult task for researchers. In this work, using a one-step spin coating approach, we have prepared a polyvinylpyrrolidone (PVP) polymer-incorporated stable phase of CsPbI₂Br at a low temperature (120 ​°C). Examinations using structural, morphological, and photo-physical measurements revealed that the optimum amount of PVP can greatly improve the optoelectronic properties of the film, which facilitates in reducing the trap states and defect in perovskite film, thus enabling charge carrier separation and suppressing charge recombination. As a result, the device based on 5 ​mg-PVP achieves a champion power conversion efficiency (PCE) of 10.47%, with a fill factor (FF) of 56.35%, a short-circuit current (J_SC) of 18.47 ​mA ​cm², and an open-circuit voltage (V_OC) of 1.01 ​V, which is significantly higher than the device without PVP (6.36%). These findings suggest that PVP-CsPbI₂Br has tremendous promise for future research and application in photovoltaic devices.