Influence of Light Soaking on FA-Rich Mixed Halide Double and Triple Cation Perovskite Absorber Layers and Efficient Inverted p–i–n Perovskite Solar Cells

Light soaking (under continuous light exposure) significantly affects the optical and electronic properties of perovskite absorbers, affecting solar cell performance over time. This study examines the effects of light soaking on two mixed-halide, mixed-cation perovskite absorber layers, namely Cs0.17FA0.83Pb(I0.9Br0.1)3 (CsFA) and Cs0.05(FA0.83MA0.17)0.95Pb(I0.9Br0.1)3 (CsMAFA) in thin films and solar cells. Optimized CsFA and CsMAFA solar cell devices achieve PCEs of 17.1% and 18.8%, respectively. Under continuous illumination, CsMAFA devices show faster stabilization of open-circuit voltage (VOC), indicating efficient charge separation and reduced non-radiative recombination. The steady-state and time-resolved photoluminescence (PL and TRPL) measurements suggest that MA reduces defect-induced recombination in CsMAFA, while both bulk and interfacial defects contribute in CsFA. Impedance measurements reveal better-aligned trap states in CsMAFA, facilitating faster charge collection and lower recombination losses, whereas CsFA exhibits slower response and higher recombination.