Effective hot-air annealing for improving the performance of perovskite solar cells

We report a simple and effective method for improving the performance of CH₃NH₃PbI_3−xCl_x perovskite solar cells. By employing a moisture pretreatment (MPT) and a novel hot-air annealing process (HAAP) for preparing the perovskite CH₃NH₃PbI_3-xCl_x film, we could successfully enhance the crystallinity of the CH₃NH₃PbI_3-xCl_x active layer and improve its photon collection properties. This led to a marked improvement in device performance. Solar cells with the structure indium tin oxide/poly(3,4-ethylenedioxythiophene) -poly(styrenesulfonate)/CH₃NH₃PbI_3-xCl_x active layer/[6,6]-phenyl-C61-butyric acid methyl ester/Ca/Al and fabricated using the MPT process and the HAAP method showed significantly improved performance, including higher power conversion efficiency (PCE) and fill factor values than those of the device fabricated conventionally. The PCE increased from 9.05 to 11.87% when the MPT process was used and from 9.05 to 15.55% when both MPT and HAAP were used. Moreover, the HAAP device did not exhibit photocurrent hysteresis, which is always observed in the case of the conventionally fabricated solar cells owing to the charge traps resulting from the low quality of the perovskite film.