Using 4‐Chlorobenzoic Acid Layer Toward Stable and Low‐Cost CsPbI₂Br Perovskite Solar Cells

Inorganic perovskite solar cells (PSCs) have attracted a lot of attention due to their thermal stability. Among them, CsPbI 2 Br are more widely studied due to their reasonable bandgap and phase stability at room temperature. However, poor moisture resistance is an urgent issue to conquer. Herein, solution‐processed 4‐chlorobenzoic acid (CBA) is used to increase the work function of a Ag electrode, enabling effective hole extraction. More importantly, CBA can effectively avoid the phase conversion of the CsPbI 2 Br perovskite from the cubic phase to the undesired nonperovskite δ‐phase due to the hygroscopicity of lithium bis (trifluoromethanesulphony)imide (Li‐TFSI) in 2,2,7,7‐tetrakis(N,N‐di‐pmethoxyphenylamine)‐9,9‐spirobifluorene (Spiro‐OMeTAD), enhancing the water stability of PSCs. It can also reduce the fabrication cost by replacing the expensive Au electrode and saving the evaporation energy consumption of the commonly used MoO 3 anode buffer layer. Consequently, the champion device achieves a power conversion efficiency (PCE) of 14.3%, with a high open‐circuit voltage of 1.21 V. After storing in air at 20% relative humidity (RH) for 500 h, the unencapsulated device maintains more than 95% of the initial PCE.