Improved open-circuit voltage and ambient stability of CsPbI₂Br perovskite solar cells by incorporating CH₃NH₃Cl

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.