Hot-substrate deposition of all-inorganic perovskite films for low-temperature processed high-efficiency solar cells

All-inorganic cesium lead halide perovskites (CsPbX3) have emerged as one of the most promising photovoltaic materials due to their superior thermal stability. However, the high phase transition temperatures (typically over 250 degrees C) of CsPbX3 perovskites are incompatible with flexible substrates. Herein, we employ a simple hot-casting method to fabricate low-temperature processed CsPbI2Br films. By casting the perovskite precursor solution onto a hot substrate (maintained at 55 degrees C), compact, largegrain and pinhole-free CsPbI2Br films can be prepared at a low post-annealing temperature, which outperform the conventional room temperature (RT)-casting and high-temperature (post-annealing at 340 degrees C) processed CsPbI2Br films containing some voids. As a result, the hot-casting and lowtemperature (post-annealing at 120 degrees C) processed CsPbI2Br perovskite solar cells (PSCs) exhibited an outstanding power conversion efficiency (PCE) of 12.5%, which is much higher than that (2.91%) of the RT-casting processed CsPbI2Br devices. Further optimization of the post-annealing temperature (optimized value: 180 degrees C) yielded the best performance of 13.8% for hot-casting processed CsPbI2Br devices. This study gives an effective and facile strategy toward low-temperature processed all-inorganic perovskite films and high-performance PSCs.