Improved stability of perovskite solar cells in ambient air by controlling the mesoporous layerElectronic supplementary information (ESI) available. See DOI: 10.1039/c5ta02843d

Recently, organometal trihalide perovskite solar cells (PSCs) have undergone intense development and show huge potential as the next generation of high efficiency photovoltaic (PV) cells. However, the stability of these devices still needs to be improved to enable commercialization, especially the photovoltaic stability under ambient conditions. In this work, the demonstrated greatly improved stability of CH 3 NH 3 PbI 3 based PSCs in ambient air has been achieved by controlling the mesoporous TiO 2 (m-TiO 2 ) layer in the devices. With the optimized thickness of the m-TiO 2 layer, rather stable devices which maintain over 85% of the initial power conversion efficiency (PCE) even after ∼2400 hours (100 days) storage in air were accomplished. It is evidenced that the suppressed decomposition of perovskite and the well-kept charge transportation are majorly responsible for the improved air-stability of the device. Through optimization of the thickness of the m-TiO 2 layer, rather stable perovskite solar cells which maintain over 85% of the initial power conversion efficiency (PCE) even after storage for 100 days in air were accomplished.