Enhanced carrier separation efficiency and performance in planar-structure perovskite solar cells through an interfacial modifying layer of ultrathin mesoporous TiO₂

The structure of interface between electron transport layer (ETL) and perovskite material is crucially important for a perovskite solar cell (PSC), especially for its carrier separation efficiency and hysteresis effect. Here, an ultrathin mesoporous TiO2 (thin-m-TiO2) layer is inserted to the interface between the compact TiO2 and the perovskite film in a planar PSC, serving as an interfacial modifying layer. The results show that the insertion of thin-m-TiO2 greatly improves the compactness and the grain size of perovskite films. Moreover, compared with traditional planar and mesoporous PSCs, the cells with an interfacial modifying layer exhibit improved performance. An average photoelectric conversion efficiency of 18.5% and a hysteresis coefficient as low as 4.5% are achieved. It is found that the interfacial modifying layer can not only enhance the carrier separation efficiency, but also maintain a high electron transport capacity. This work provides a feasible and facile strategy for developing high-performance PSCs.