ABSTRACT
We propose a doping method by using [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) to fill the grain boundary interstices of the methylammonium lead iodide (CH3NH3PbI3) perovskite for the elimination of pinholes. A sandwiched PCBM layer is also used between the perovskite and TiO2 layers to improve the interfacial contact. By using these two methods, the fabricated perovskite solar cells show a low hysteresis effect and high current density, which result from the improved compactness at the grain boundaries of the perovskite surface and the interface between the TiO2/perovskite layers. The theoretical and experimental results indicate that PCBM can effectively suppress carrier recombination, regardless of the interfacial layer or dopant. We also found that the dark current reduced during the analysis of dark state current-voltage ( I- V) characteristics. The slopes of the I- V curves for the fluorine-doped tin oxide/PCBM-doped perovskite/Au device reduce monotonically with the increase in the PCBM concentration from 0.01 to 0.1 wt %, which suggest the decreasing defects in the perovskite layer. By tuning the PCBM doping and controlling the preparation process, we have successfully fabricated a planar TiO2/PCBM-based PCBM-doped perovskite photovoltaic device that reaches a high current density of 22.6 mA/cm2 and an outstanding photoelectric conversion efficiency up to 18.3%. The controllability of the PCBM doping concentration and interfacial preparation shed light on further optimization of the photoelectric conversion efficiency of perovskite solar cells.
