How the dynamics of attachment to the substrate influence stress in metal halide perovskites

Metal halide perovskites have the potential to contribute to renewable energy needs as a high efficiency, low-cost alternative for photovoltaics. Initial power conversion efficiencies are superb, but improvements to the operational stability of perovskites are needed to enable extensive deployment. Mechanical stress is an important, but often misunderstood factor impacting chemical degradation and reliability during thermal cycling of perovskites. In this manuscript, we find that a commonly used equation based on the coefficient of thermal expansion (CTE) mismatch between perovskite and substrate fails to accurately predict residual stress following solution-based film formation. For example, despite similar CTEs there is a 60 MPa stress difference between narrow bandgap “SnPb perovskite” Cs0.25FA0.75Sn0.5Pb0.5I3 and “triple cation perovskite” Cs0.05MA0.16FA0.79Pb(I0.83Br0.17)3. A combination of in situ absorbance and substrate curvature measurements are used to demonstrate that partial attachment prior to the anneal can reduce residual stress and explain wide stress variations in perovskites.