Polyhydroxy compound modifying SnO2 for high-performance and stable perovskite solar cells

Electron transport layer (ETL) is one of the key functional layers for extracting carriers in perovskite solar cells (PSCs). SnO2 with high electron mobility and excellent energy level matching with adjacent perovskites has been considered an ideal electron transport material with great application prospects. However, surface defects always exist on the SnO2 films prepared by solution method, which will inevitably lead to non-radiation recombination at the interface of SnO2 ETL/perovskite. To further improve the performance of PSCs, the defects should be effectively suppressed. Herein, an interfacial engineering strategy is adopted to eliminate the surface defects and improve the interface performance by passivating the SnO2 electron transport layer with sodium L-ascorbate (SLA). After the SLA treatment, the interfacial defects of SnO2/perovskite film were reduced significantly and the electron transport was effectively facilitated by the denser SnO2 layer, finally improving the power conversion efficiency (PCE) of PSCs. Besides, SLA neutralized the alkalinity of SnO2 film, simultaneously improving the efficiency and stability of the device. As a result, the PCE of FA0.74MA0.19Cs0.07PbI2.81Cl0.19 PSCs with active area of 0.09 cm2 was increased from 20.32 % to 22.70 %, and the larger area PSCs with active area 1.00 cm2 obtained a high PCE of 19.83 %. This work presents a convenient and effective passivation strategy for improving the ETL to promote the development of perovskite photovoltaic devices.