Strengthened Perovskite/Fullerene Interface Enhances Efficiency and Stability of Inverted Planar Perovskite Solar Cells via a Tetrafluoroterephthalic Acid Interlayer

In this work, a novel back contact interface engineering is developed for inverted planar perovskite solar cells, in which a tetrafluoroterephthalic acid (TFTPA) interlayer is inserted between CH3NH3PbI3 and PC61BM to strengthen the interface contact. Benefiting from the strong Coulombic interactions between positive electron-poor tetrafluoroterephthalate moieties and negative electron-rich fullerene molecules, as well as the coordinate effect between −COOH groups of TFTPA and Pb2+ ions of perovskites surface, a tightly jointing and defect-passivated CH3NH3PbI3/PC61BM interface is formed. The strengthened CH3NH3PbI3/PC61BM back contact can significantly facilitate electron transport and simultaneously diminish the charge accumulation and recombination. Therefore, power conversion efficiency (PCE) of the TFTPA device is up to 19.39%, whereas the hysteresis effect is weak, and the PCE is improved by 20.4% compared with the control device which does not have a TFTPA interlayer. Particularly, the moisture stability of the TFTPA device is greatly improved as compared to the control device. Our findings illustrate that the back contact interface engineering is an important and promising approach for inverted planar perovskite solar cells.