Unraveling the Combined Photothermal Stability of Common Perovskite Solar Cell Compositions

In halide perovskite solar cells, certain compositions, especially those with a high mixture of anions, degrade rapidly. Here, a degradation study compares the photo (exposure to light), thermal (exposure to elevated temperatures), and photo-plus-thermal (combination) stability of three representative perovskite compositions chosen for their relatively high performance and to independently test anion versus cation effects. Based upon experience and reports, the compositions studied are triple cation with a high Br ratio (Cs0.05(FA0.98MA0.02)0.95Pb(I0.5Br0.5)3), all iodide with a moderately high Cs ratio (FA0.8Cs0.2PbI3), and FA-dominated triple cation (Cs0.05(FA0.98MA0.02)0.95Pb(I0.98Br0.02)3). Cs0.05(FA0.98MA0.02)0.95Pb(I0.98Br0.02)3 displayed the best combined photo-plus-thermal stability. Degradation mechanisms were investigated by comparing the morphology, surface composition, and bulk and interface carrier dynamics. Under the harshest aging conditions (photo-plus-thermal), phase segregation and vaporization of organic cations occurred, along with the appearance of high-energy states indicating the interaction with C60. The findings were verified on perovskite films blade-coated in air used in devices (FTO/NiOx/SAM/Perovskite/C60/BCP/Cu), achieving an efficiency of 21.9% alongside correlated stability.