Surface engineering for injection control and hysteresis reduction in Perovskite Solar Cells

Abstract

Hybrid halide perovskites, such as CH3NH3PbI3 are among the most promising absorbers materials in photovoltaics due to its direct band gap, high absorption coefficient and low charge recombination.1,2 In addition, they have the benefits of being prepared by low temperature solution processes which are low cost.3,4 However, the interfaces between the perovskite and the selective contacts are still decisive for obtaining a better performance of the device. In addition, interfaces also play a critical role on the hysteresis present in the J-V curves that has been detected in Perovskite Solar Cells (PSCs), indicating that the current is dependent on the direction and speed of the scanning.5,6 Modifying the electron selective contact with a self-assembled monolayer (SAM) of fullerene derivatives has shown to enhance the photocurrent and to have a positive effect on the hysteresis, as reported for example by Wojciechowski et al.7 This fullerene derivative contains a functional group to anchor, by chemisorption, onto the selective contact surface, modifying the interface and improving the electron extraction.8 This work is focused on the use of some fullerene derivatives containing different functional groups to anchor onto the scaffold and the compact layer of TiO2. In addition, the effect of removing the compact layer has been studied in combination with the use of fullerenes.