Insights into Accelerated Degradation of Perovskite Solar Cells under Continuous Illumination Driven by Thermal Stress and Interfacial Junction

The operational stability of encapsulated halide perovskite solar cells (HaPSCs) is imperative for their commercialization. Despite improvements in device stability, we lack insights into the irreversible degradation of devices under prolonged illumination and heat stress. Here, we investigated the operational stability of devices (∼1 cm2) made with poly(triaryl amine) (PTAA; power conversion efficiency PCE ≈ 19.32%) and sputtered NiOx (PCE ≈ 15.60%) as a hole-transport layer (HTL) under light (for >1000 h) at 20, 60, and 85 °C to unravel the degradation mechanisms. Degradation of the PTAA device was accelerated by interface deterioration and bulk decomposition initiated by the formation of voids and PbI2 via iodine migration from defective regions at the columnar grain boundaries with the release of I2 gas. The NiOx device, with its immunity to iodine and its moisture-resistive properties, had significantly improved stability with suppression of the HaP bulk degradation by alleviation of internal defect dynamics. Our results corroborate that the formation of voids and PbI2 crystallites at columnar intergrains or at the HTL (ETL) /HaP interface with the release of I2 gas is the primary cause of device degradation. Capacitance–voltage analysis showed that the PTAA device develops a much wider defective interface layer than the NiOx device, driven mainly by the chemical reaction of iodine with the interfacial layer. Thus, our results reveal that although the cracking of columnar intergrains and defective spots in the perovskite bulk is the main origin of device degradation, the nature of the carrier transport layer also partly contributes to catalyzing bulk and interface degradation. Thus, the passivation of columnar intergrain defects in the HaP bulk and lamination of the interface with a chemically inert to iodine and a moisture-resistive carrier-selective layer is crucial to the operational stability of HaPSCs.