A halide exchange engineering for CH3NH3PbI3−xBrx perovskite solar cells with high performance and stability

A facile halide exchange route based on CH 3 NH 3 Br solution post-treatment has been successfully employed to transform the two-step spin-coated CH 3 NH 3 PbI 3 films into the CH 3 NH 3 PbI 3− x Br x films, whose morphologies and compositions could be modified simultaneously. With the increase of CH 3 NH 3 Br solution concentration, the CH 3 NH 3 PbI 3− x Br x films exhibited increased grain size, prolonged charge carrier lifetime, and enlarged bandgap with slightly reduced light absorption compared with the parent CH 3 NH 3 PbI 3 film. The mesostructured perovskite solar cells based on the CH 3 NH 3 PbI 3− x Br x films yielded the optimal power conversion efficiency (PCE) of 14.25%, which is much higher than that of device with the parent CH 3 NH 3 PbI 3  film. In particular, the device based on the CH 3 NH 3 PbI 3− x Br x film retained up to 93% of its original PCE after exposed to air for 14 days without any encapsulation, presenting a favorable stability. Our work suggests a novel and attractive way to fabricate high-performance perovskite solar cells with excellent stability.