Crystallization Kinetics Engineering toward High-Performance and Stable CsPbBr3-Based Perovskite Solar Cells

Due to their superior stability and high open-circuit voltage (V-oc), all-inorganic cesium lead bromine (CsPbBr3) perovskite solar cells are attractive for tandem device applications. However, the current methanol fabrication process requires multistep (at least 5-6 times) spin coating, which is tedious and time-consuming. Here, we introduced a modified two-step spin-coating method to prepare the CsPbBr3 films. Water, instead of methanol, has been selected as the solvent for CsBr. Via precisely controlling the loading time (t) of CsBr aqueous solution on the PbBr2 film surface, the prepared films can be tuned from a CsPbBr3@CsPb2Br5 phase (t < 15 s) to a well-crystallized CsPbBr3 phase (t similar to 15 s) and finally the CsPbBr3@Cs4PbBr6 phase (t > 15 s). With a loading time of 15 s, we yield a maximum power conversion efficiency (PCE) of 9.14%, which is comparable with the devices fabricated from the methanol process. In addition, a high fill factor (FF) of 0.84 with a PCE of 9.02% has been obtained, which is among the highest FF reported for CsPbBr3 devices. Moreover, the devices hold superior stability with their PCEs slightly dropped under humidity and high temperature during a 30 day aging test. Overall, this facile and simple fabrication method reported in this work shows great potential for practical applications in the future.