Interface regulation enables hysteresis free wide-bandgap perovskite solar cells with low VOC deficit and high stability

Wide-bandgap perovskites (WBPs) are attractive candidates for constructing tandem photovoltaic devices, but they are often much more prone to defect formation and other interfacial problems. Fixing these problems can boost the performance of WBP solar cells and is thus crucial for achieving a high overall energy conversion efficiency. Toward this end, we performed a systematic study on the construction of a 2D/3D heterostructure on the WBP surface to passivate the defects and to regulate the interfacial properties by varying the chain length of alkylammonium bromides in the 2D part. Hexanelammonium bromide (HABr) was found to be the champion in multiple respects. The optimized interfacial energy band structure and the reduced defect density with HABr allowed to achieve a remarkable 19.8% photovoltaic efficiency with a prominent open-circuit voltage (VOC) of 1.31 V. HABr also reduced interfacial capacitance by improving hole transport, substantially alleviating the hysteresis of the corresponding devices. Last but not least, the HABr-induced hydrophobicity in the 2D layer can not only block moisture, but also retard migration of the alkali cations from the perovskites across the interface, eventually endowing the WBP based devices with a superior moisture stability.