Low-temperature solution-processed Li-doped SnO₂ as an effective electron transporting layer for high-performance flexible and wearable perovskite solar cells

Lead halide perovskite solar cells (PSCs) are thought to be promising energy power suppliers because of their feasibility for high power conversion efficiency (PCE), light weight, and flexible architecture. The preparation of charge transporting layers at low temperature has been essential for high-performance and flexible PSCs. Recently, low-temperature-processed metal oxides have been a desirable material for charge transport and air stability for PSCs, instead of organic semiconductors. However, pristine metal oxides fabricated at low temperature have still precluded high performance of the device because of their low conductivity and large deviation in energy levels from the conduction band or valance band of the perovskite. Therefore, doping metals in the metal oxides has been considered as an effective method to endow suitable electrical properties. Herein, we developed a highly efficient electron transporting layer (ETL) comprising Li-doped SnO₂ (Li:SnO₂) prepared at low temperature in solution. The doped Li in SnO₂ enhanced conductivity as well as induced a downward shift of the conduction band minimum of SnO₂, which facilitated injection and transfer of electrons from the conduction band of the perovskite. The PCE was measured to be 18.2% and 14.78% for the rigid and flexible substrates, respectively. The high-performance and flexible PSCs could be potentially used as a wearable energy power source.