Thermal Stability of Lead-Halide PSCs Toward Space Applications—Investigating the Impact of Thermal Fatigue on the ETL-Perovskite Interface

Lead-halide perovskites (LHPs) have become the focus of emerging photovoltaics due to favorable properties like high carrier mobility, defect tolerance, and tunable bandgap - which are the cause for their rapid increase in power conversion efficiency (PCE) in the last decade. However, LHPs possess intrinsic thermal instability which induces rapid degradation in films and solar cell devices. Under high temperature conditions, LHP thin films degrade via ion migration and transition into a photo-inactive phase. When Perovskite Solar Cells (PSCs) are placed under such conditions, CTE mismatch between material layers of about one order of magnitude generates overwhelming forces and induces microscopic and macroscopic failure. Within interlayers (the junction between two layers), CTE mismatch can cause detrimental strain on bonds, eventually causing them to break. This significantly decreases performance by reducing charge transfer and leads to macroscopic adhesion failure where entire layers can delaminate or wrinkle. However, the behavior of PSCs under low-to-high temperature cycling still requires further investigation. Here, we investigate the impact of surface interactions on thermomechanical integrity throughout the device under thermal and mechanical fatigue. Literature suggests that substrate rigidity heavily influences the stress relaxation mechanism present, whether delamination or wrinkling. The role of substrate rigidity on stress relaxation under mechanical cycling will be examined via compression testing. Likewise, the integrity of interlayer bonds under thermal fatigue will be examined via temperature cycling in a thermal-vacuum chamber and XPS, XRF, and electronic performance measurements before and after thermal aging.