Performance improvement of planar perovskite solar cells with cobalt-doped interface layer

Abstract

Metal element doping can effectively overcome the drawbacks of transition metal oxide electron transport layer (ETL), such as point defects and unmatched band structure, thereby improving the charge transport and extraction capacity of perovskite solar cells (PSCs). Herein, the application of Co (III) doped compact TiO2 layer for planar heterojunction PSCs is demonstrated. The Co ions replace the Ti ions, which can reduce the oxygen vacancy defects in pristine TiO2, thus decreasing the carrier recombination in electronic trap states and enabling faster electron transport and collection. Co (III) doping can also reduce the work function of TiO2 ETL and adjust its band structure to form a better level alignment, which is beneficial to improving the electron extraction capacity by decreasing the barrier against the electron transport. Meanwhile, the TiO2 ETL with smoother surface leads to a good interface contact. Correspondingly, the quality of perovskite film is also improved. An overall rise of the open-circuit voltage, short-circuit current density and the fill factor are realized, yielding an increased PCE from 16.86% to 19.16%. Our work provides a facile and effective method to solve the problems of non-stoichiometry defects and energy level mismatching for TiO2 or other metal oxide semiconductors transport layer.