Improving Stability of Triple-Cation Perovskite Solar Cells under High-Temperature Operation

Metal halide perovskite (MHP) photovoltaic performance required for commercial technology encompasses both efficiency and stability. Advances in both these parameters have recently been reported; however, these strategies are often difficult to directly compare due to differences in perovskite composition, device architecture, fabrication methods, and accelerated stressors applied in stability tests. Reported strategies to increase efficiency of perovskite photovoltaics include ink additives, pre- or post-treatments to the perovskite absorber, and choice of contact materials. While these methods may be effective for boosting the initial performance of MHPs, there is a distinct lack of standardized accelerated stability testing data showing the effects of these modifications on the operational stability. This work focuses on using individual and combinations of additive, post-treatment, and contact layer strategies from recent perovskite literature reports. A standardized accelerated testing protocol of light, heat (70 °C), and bias (modified ISOS-L-2) was applied throughout this study to evaluate overall performance impact across device architectures.<br/><br/>Initially, CsMAFA perovskites with an ink stoichiometry of Cs_0.05MA_0.16FA_0.79Pb(I_0.84Br_0.16)₃ were investigated. Visible degradation was quickly observed across all devices tested with this composition. Time of flight secondary ion mass spectrometry (ToF-SIMS) analysis revealed lateral phase halide phase segregation under these elevated temperature test conditions, which was not induced at lower temperatures. Reduction of the bromine content on the X site to a composition of Cs_0.05MA_0.16FA_0.79Pb(I_0.92Br_0.08)₃ mitigated this effect and provided a baseline platform for the broader study of additives, post-treatments, and alternative transport layers to determine the effect the interaction of each has on the stability of the device.<br/><br/>Through analysis of over 1000 devices, we identify the hole transport layer as the most significant factor toward improving performance at elevated temperature. Out of all the combinations tested, the four most stable architectures incorporated a NiOx contact. Post-treatment approaches targeting the perovskite/ETL interface showed positive effects on the initial performance of TC8Br devices but did not lead to significant stability improvements. This observation highlights that passivation approaches for perovskite solar cells should more regularly undergo accelerated aging tests that include exposure to light and heat to unambiguously establish whether the proposed passivation approach is worthwhile. Fundamentally, we observe that these p–i–n devices are stability limited by the HTL, consistent with recent trends in literature. This work therefore motivates the continued development of high-performance HTLs to realize stable and efficient perovskite solar cells.