JungYup Yang

Multiple‐cation perovskites have been extensively researched for stability enhancement, but limited literature exists on CsFAMA (CFM) solar cell stability under harsh temperature and humidity. This article focuses on the development of damp‐heat‐resistant CFM‐based perovskite solar cells (PSCs) through the implementation of various surface treatment strategies, including antisolvent treatment (AST) control and alkyl‐type interfacial passivation, while also proposing an effective encapsulation structure. The Cs + ratio in Cs x (FA 0.91 MA 0.09 ) 1− x Pb(I,Br) 3 perovskites is varied in the range of x = 0 to 0.362, and the AST times are explored by adjusting from 8 to 15 s. Remarkably, a power conversion efficiency (PCE) is achieved with significant improvements in open‐circuit voltage and fill factor at an AST time of 12 s. Through precise tuning of the Cs ratio to x = 0.17 (Cs 0.17 (FA 0.91 MA 0.09 ) 0.83 Pb(I,Br) 3 ) and introduction of an octyl‐ammonium iodide interlayer, the highest‐performing device with a PCE of 20.82% is obtained. Additionally, a low‐temperature vacuum lamination is employed, and the conducive tape in a twisted form is extended, which effectively seals the device. This results in superior stability for 500 h under damp‐heat conditions at 85 °C and 85% relative humidity. This encapsulation method holds significant promise as a potential solution for the modularization of PSCs.