Efficient and Stable Perovskite Solar Cells with SnO2/TiO2 Bilayer Electron Transport Architectures

Perovskite solar cells (PSCs) have drawn widespread concern for their high efficiency and facile low-temperature solution fabrication, promising for the alternative low-cost photovoltaic energy. However, commercial deployment requires resolution of persistent stability issues and electrical hysteresis effects in PSCs. We demonstrate planar PSCs configuration using a stacked SnO2/TiO2 electron transport layer, which exhibits a cascadealigned energy level, achieving an efficiency of 23.54% with a reduced hysteresis (index: 0.12) and remarkable stability (>90% efficiency retention beyond fifty days at 25% relative humidity without encapsulation). Photoluminescence and electrical characterizations suggest that the performance enhancement is ascribed to the synergetic optimization from suppressing the defective interface and promoting carrier transfer and blocking. More importantly, detailed transient absorption characterization reveals that the use of stacking n-type materials can decrease the hot-carrier cooling dynamics, improve the carrier transfer, and eliminate nonradiative recombination in PSCs. These results suggest that stacking n-type layers could enable superior overall performances compared to common electron transport layers (TiO 2 and SnO 2 ), providing facile routes for fabricating efficient PSCs with high stability.