Green low-temperature-solution-processed in situ HI modified TiO2/SnO2 bilayer for efficient and stable planar perovskite solar cells build at ambient air conditions

Planar structures for halide perovskite solar cells with the high efficiencies typically use high-temperature processed TiO 2 as the electron transporting layers (ETLs). Here, we demonstrate that an in-situ passivation strategy for TiO 2 film through the introduction of HI during low-temperature preparation process. HI not only controls hydrolysis of TiO 2 precursor but also eliminates defects and suppresses trap states in TiO 2 film. Meanwhile, the double-layer architecture is constructed by coating TiO 2 with SnO 2 layer, the double ETLs can improve the photovoltaic performance of methylamine lead iodide (MAPbI 3 ) perovskite solar cells. The TiO 2 (HI)/SnO 2 ETL can effectively reduce the interfacial charge recombination and facilitate electron transfer. More importantly, the preparation of TiO 2 and SnO 2 are totally performed at low-temperature (150 °C) and the devices are fabricated in uncontrolled ambient conditions. Our best-performing planar perovskite cell using such a TiO 2 (HI)/SnO 2 ETL has achieved a maximum power conversion efficiency (PCE) of 16.74%, and the devices exhibit good stability which maintaining 85% and 83% of their initial efficiency after heating at 100 °C for 22 h and under illuminating upon 1 sun irradiation for 6 h, respectively. Our results suggest a new approach for further improving the stability of PSCs fabricated in the air condition.