Reducing the interfacial defects of perovskite films is key to improving the performance of perovskite solar cells (PSCs). In this study, two kinds of perylene monoimide (PMI) derivative phosphonium bromide salts were designed and used as a multifunctional interface-modified layer in PSCs. These two molecules are inserted between SnO2 and perovskite to produce a bidirectional passivation effect. The interaction with SnO2 reduces the oxygen vacancy on the surface of SnO2 and tunes the energy level of the electron transport layer, making more matches with the perovskite layer. The modified layer can promote the growth of perovskite crystals and reduce the interfacial defects of the perovskite film. Furthermore, the power conversion efficiency (PCE) of PSCs increased from 19.49 to 22.85%, and the open-circuit voltage (VOC) increased from 1.06 to 1.14 V. At the same time, the PCE of the SnO2/PMI-TPP-based device remained 88% of the initial PCE after 240 h of continuous illumination. In addition, these two PMI derivatives with a quasi-planar structure can improve the flexibility of flexible PSCs. This study provided a new strategy for the interfacial modification of PSCs and a new insight into the application of flexible PSCs.
Keywords: PMI derivatives; defect passivation; interface modification; level optimization; perovskite solar cells.