LAUSR

The effects of compositions on the crystalline structures, microstructures and optical characteristics of perovskite CH3NH3PbI3 films were investigated via varying the molar ratios of CH3NH3I (MAI) to PbI2 in the precursor solutions. As the amounts of MAI were increased in the precursor solution, the formation of CH3NH3PbI3 was facilitated, and the grain sizes as well as absorbance of the resulting films were increased. The enlarged grain of the prepared films effectively suppressed the carrier recombination at grain boundary and improved the electrical performance of the fabricated solar cells. The analysis of diode parameters also revealed that the additional shunt path was suppressed. On the other hand, once the molar ratio of MAI to PbI2 was further increased, the roughness of film surface was increased and caused the carrier recombination between absorber layers and hole-transport layers, thereby resulting in a dramatic decrease in conversion efficiency. This investigation indicated that controlling the compositions in the precursors of CH3NH3PbI3 films is crucial to improve the photovoltaic properties of perovskite solar cells.