Healing the defects in CsPbI₃ solar cells by CsPbBr₃ quantum dots

Cesium lead iodide (CsPbI₃) is a promising photo-absorber for perovskite photovoltaics due to its high thermal stability and relatively small bandgap. However, there are many defects in solution processed polycrystalline CsPbI₃ films especially at the grain boundaries (GBs), which limit the power conversion efficiency (PCE) of CsPbI₃ solar cells. In this work, we introduced CsPbBr₃ quantum dots (QDs) on top of the CsPbI₃ film to passivate the defects. As CsPbBr₃ QDs have a small size and a similar crystal structure as the CsPbI₃, they are excellent modifiers to fill in the GBs and heal the defects. Moreover, we find there is an anion exchange reaction between the CsPbBr₃ QDs and CsPbI₃ films, which is evidenced by photoluminescence spectra and grazing incidence X-ray diffraction patterns. The QDs treated films show enhanced carrier lifetime and reduced defect density. Additionally, the ligands on CsPbBr₃ QDs increase the hydrophobicity of the films. As a result, the QDs treated CsPbI₃ solar cells prepared at high temperature obtain PCEs exceeding 16% with high stability.