Perovskite/P3HT graded heterojunction by an additive-assisted method for high-efficiency perovskite solar cells with carbon electrodes

The absence of hole transport layers (HTLs) in the carbon-based perovskite solar cells (PSCs) limits the further improvement of its power conversion efficiency (PCE) and future commercialization. Here we adopted a convenient one-step additive-assisted method to treat perovskite layers by adding poly(3-hexylthiophene) (P3HT) in chlorobenzene with concentration optimized. The incorporation of P3HT tremendously facilitates the crystallinity and passivates the defects of the perovskite film, which suppresses carrier recombination efficiently. In addition, the resulting perovskite/P3HT graded heterojunction enhances hole extraction capability, which leads to the PCE improvement from 12.72% to 15.57%. We also fabricated flexible devices and the PCE increases from 11.81% to 13.54%, which suggests our strategy is suitable for flexible devices. This study paves an efficient strategy of heterojunction for highly efficient carbon-based PSCs without additional hole transport layer.