Novel insight into the function of PC61BM in efficient planar perovskite solar cells

A thin PC 61 BM buffer layer (BL) has been introduced between TiO 2 electron transporting layer and perovskite absorber in n-i-p planar perovskite solar cells (PSCs). We have found that the elastic nature of the PC 61 BM BL promotes the formation of porous PbI 2−x Cl x thin film with loose structure, which is vital in the following formation of high quality, uniform perovskite films with large grain size. In addition, it has been demonstrated that the thin PC 61 BM BL also flattens the TiO 2 surface, passivates the defects or dangling bands parasitizing on the TiO 2 surface, and optimizes the device band alignment. As a result, the device efficiency has been enhanced dramatically from ~8.37% to 15.44%. Moreover, devices show a good stability over 400   h and reproducibility in 20 pieces fabricated with the same procedure, which implies that this finding is benefit for fabricating highly efficient PSCs. We introduced a thin PC 61 BM buffer layer between the TiO 2 electron transport layer and the perovskite absorber in n-i-p planar perovskite solar cells , which facilitates the construction of a porous PbI 2−x Cl x precursor film, and thus promotes the following realization of high quality, uniform perovskite films with large grain size and improves the solar cell efficiency significantly.