CsCl-induced defect control of CsPbI2Br thin films for achieving open-circuit voltage of 1.33 V in all-inorganic perovskite solar cells

All-inorganic perovskite solar cells (PSCs) attract attention due to their excellent optical properties and high thermal stability, but energy loss is a challenge due to the trap-assisted recombination loss at the imperfect film morphology. We herein demonstrate the optimization of α-CsPbI2Br morphology including low defect density and large grain size by employing cesium chloride (CsCl) as an additive. High-quality CsPbI2Br film grown with CsCl reveals high crystallinity and largely-grained morphology, which provides reduced defect density and energy loss. As a result, we optimize the CsPbI2Br device with 1% CsCl additive, which shows a power conversion efficiency (PCE) of 11.04% with an open-circuit voltage (VOC) of 1.33 V. The CsPbI2Br with CsCl shows stability maintaining >80% of the initial efficiency being aged for >360 h in ambient atmosphere. The CsCl-employed device also retains 98% of initial PCE after being heated at 85 °C for 12 h, verifying enhanced stability of the all-inorganic PSCs. In addition, the photovoltaic performance under white light-emitting diode yields PCE over 25% with a high V OC of 1.08 V in the presence of CsCl, which realizes the stable all-inorganic PSCs applicable in outdoor/indoor environments.