Degradation Kinetics of Inverted Perovskite Solar Cells

We explore the degradation behaviour under continuous illumination and direct oxygen exposure of inverted unencapsulated formamidinium(FA)(0.83)Cs(0.17)Pb(I(0.8)Br(0.2))(3), CH(3)NH(3)PbI(3), and CH(3)NH(3)PbI(3−x)Cl(x) perovskite solar cells. We continuously test the devices in-situ and in-operando with current-voltage sweeps, transient photocurrent, and transient photovoltage measurements, and find that degradation in the CH(3)NH(3)PbI(3−x)Cl(x) solar cells due to oxygen exposure occurs over shorter timescales than FA(0.83)Cs(0.17)Pb(I(0.8)Br(0.2))(3) mixed-cation devices. We attribute these oxygen-induced losses in the power conversion efficiencies to the formation of electron traps within the perovskite photoactive layer. Our results highlight that the formamidinium-caesium mixed-cation perovskites are much less sensitive to oxygen-induced degradation than the methylammonium-based perovskite cells, and that further improvements in perovskite solar cell stability should focus on the mitigation of trap generation during ageing.