Improved open‐circuit voltage and ambient stability of CsPbI 2 Br perovskite solar cells by incorporating CH 3 NH 3 Cl

Inorganic cesium metal halide perovskites have gained research interest as absorbers in perovskite solar cells due to their superior thermal stability. Among these, CsPbI2Br, with a narrower band gap than CsPbBr3 and a better phase stability than CsPbI3, has received tremendous interest of the researchers. However, CsPbI2Br takes adverse phase transfer easily with an exposure to the water vapor in ambient air which not only brings inconvenience for researches but also puts forward very high requirement for encapsulation. Herein, a dense and uniform film is obtained by incorporating hydrophobic CH3NH3Cl (MACl) into the precursor solution. Being attributed to a good passivation effect, the defect density is decreased from 3.12 × 1016 to 1.49 × 1016 cm−3 and the average photoluminescence lifetime is increased from 8.84 to 20.6 ns. The photovoltaic device achieves a high open-circuit voltage of 1.22 V based on optimized MACl-doped film and accordingly a higher power conversion efficiency (PCE) of 12.9% which is 21.7% higher than the pristine CsPbI2Br device with PCE of 10.6%. In addition, the ambient stability of MACl-doped device has been enhanced, which is greatly attributed to the hydrophobic properties of MACl. This work provides a clue to improve ambient stability of inorganic perovskite solar cells and inspires toward further development of this material.