Efficient and stable planar hole-transport-material-free perovskite solar cells using low temperature processed SnO2 as electron transport material

Efficient and stable planar hole-transport-layer-free perovskite solar cells were fabricated using low temperature processed tin dioxide (SnO2, 180 degrees C) as electron-transport-material and carbon film (100 degrees C) as top electrode. Open circuit voltage of 1.03 +/- 0.02 (highest at 1.07) V was obtained, which was 100 mV higher than that of reference devices using conventional high-temperature-processed mesoporous TiO2 as electron-transport-material, or 0.91 +/- 0.03 (highest at 0.96) V. The increased open circuit voltage along with slightly-upgraded fill factor then helped to upgrade power conversion efficiency to 13.21 +/- 0.7% (highest at 14.5%) under simulated illumination of AM 1.5 G, 100 mW/cm(2), compared to 10.13 +/- 1.34% (highest at 10.46%) of the reference devices. The improvement is ascribed to the upgraded built-in potential. Mott-Schottky study showed that, using low-temperature-processed SnO2 as electron-transport-material, higher built-in-potential (0.94 V) could be obtained, compared with 0.89 V of TiO2 based device, which then retarded charge recombination and thus increased both of the open circuit voltage and fill factor. Meanwhile, stability was test. Without any encapsulation, storage stability up to 150 days (3600 h, the test is still on-going) has been obtained for devices kept in dark (relative humidity similar to 45%), which is contributed by the low photo-activity SnO2, and the adoption of formamidinium cations, bromide anions co-doped perovskite film.