We explore the degradation behaviour under continuous illumination and direct oxygen exposure of inverted unencapsulated formamidinium(FA)0.83Cs0.17Pb(I0.8Br0.2)3, CH3NH3PbI3, and CH3NH3PbI3-xClx 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 CH3NH3PbI3-xClx solar cells due to oxygen exposure occurs over shorter timescales than FA0.83Cs0.17Pb(I0.8Br0.2)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.
@article{arxiv.1801.09761,
title = {Degradation Kinetics of Inverted Perovskite Solar Cells},
author = {Mejd Alsari and Andrew J. Pearson and Jacob Tse-Wei Wang and Zhiping Wang and Augusto Montisci and Neil C. Greenham and Henry J. Snaith and Samuele Lilliu and Richard H. Friend},
journal= {arXiv preprint arXiv:1801.09761},
year = {2018}
}