Low temperature fabrication of formamidinium based perovskite solar cells with enhanced performance by chlorine incorporation

•Formamidinium based perovskite solar cells were fabricated with an inverted device structure at low temperature.•Chlorine incorporation significantly improves the quality of perovskite films with larger grains and high crystallinity.•The device was successfully demonstrated on flexible substrates with PCE of 9.9%.

Recently formamidinium (FA) based perovskite solar cell was demonstrated to show high performance and better stability upon partial substitution of FA with Cs cation. However, the fabrication of device required high-temperature processing on TiO2 electrode and thus limits the use of flexible polymeric substrates. Here, we present a low temperature approach for the fabrication of p-i-n perovskite solar cells based on Cs0.15FA0.85PbI3. Furthermore, we investigated the effects of chlorine on the morphology and crystallinity of the perovskite films and the corresponding photovoltaic performance. Chlorine incorporation can significantly enlarge the size of grains and improve the crystallinity of perovskite films with full surface coverage. A best power conversion efficiency of 14.5% was realized for planar perovskite solar cells with negligible hysteresis and remarkable reproducibility.

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