Enhancing the performance of planar organo-lead halide perovskite solar cells by using a mixed halide source

Cl incorporation has been reported to be able to significantly increase the diffusion length of carriers in organo-lead halide perovskite thin films. However, due to the low solubility of PbCl2, Cl incorporation has been rarely reported in a two-step process, which is capable of producing uniform organo-lead halide perovskite thin films. In this letter, we report a novel growth method that combines the two-step process and Cl incorporation. The Cl-incorporated organo-lead halide perovskite solar cell made from a two-step process demonstrated a power conversion efficiency of 10.5%, which is 27% higher than that without Cl incorporation. Further investigation was performed to explore the fundamentals of the enhancement. Kelvin probe force microscopy (KPFM) measurement revealed a larger band bending at grain boundaries with Cl incorporation, which brings the Fermi level of the bulk perovskite thin film closer to the center of the bandgap. As a result, a p-i-n type of junction is formed in the devices with Cl incorporation, which facilitates the charge carrier collection. Additional carrier lifetime measurements indicate that the electron lifetime in the perovskite thin film with Cl incorporation is longer, indicating reduced recombination in the devices with Cl incorporation.