This study utilizes a method to enhance the structural and thermal stability of perovskite solar cells (PSCs) by incorporating an alkali halide interlayer between the electron transport layer (ETL) and perovskite, which is known to improve device efficiency. This passivation technique significantly reduces residual stress within the perovskite at room temperature (3.68 MPa → 2.56 MPa) and maintains structural integrity under thermal cycling (-40 to 85 °C) as per IEC 61215: 2016 standards. Following 50 cycles, the treated film exhibits a minimal increase in residual stress (≈5.34 MPa), in contrast to the control film (≈29.72 MPa) based on Williamson-Hall 2θ - Sin