Thermal Stress Mitigation and Improved Performance in Perovskite Solar Cells via Lattice Matched Alkali Halide Passivation

Abstract 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 2 Ψ analysis. The incorporation of wide‐bandgap alkali halides facilitates a strong lattice registry, thereby enhancing structural reliability. Moreover, fluorescence lifetime imaging microscopy (FLIM) confirms a reduction in defect formation, correlating with macroscopic lifetime studies. This also increases open circuit voltage ( V OC ) (1.08 V → 1.15 V) and device efficiency (17.9% → 20.6%). Notably, the treated device retains ≈71% of its initial PCE after 50 thermal cycles, whereas control devices ceased operation after 30 cycles due to thermal stress‐induced interfacial delamination. This approach effectively prevents interlayer delamination, improving long‐term structural reliability and, thereby, enabling efficient and thermally stable PSC deployment.