Reducing Open-circuit Voltage Deficit of Wide-bandgap Perovskite Solar Cells by Heterocyclic Amine Modification

Wide-bandgap (WBG) perovskites play a key role in multi-junction tandem solar cells, which have greater potential in delivering higher power conversion efficiencies than single-junction devices. However, WBG perovskite solar cells suffer from relatively high open-circuit voltage (V_OC) loss due to their high surface defect density and interfacial energy band mismatch. Here, we found the heterocyclic amines with stronger electron donating ability are able to better passivate the defects by proton exchange and coordination reaction, as well as facilitating the electron transfer on the interface between the perovskite and electron transporting layer by regulating the band structure. After comparison, the piperazine modified WBG perovskite solar cells exhibit power conversion efficiency of 19.5% with high V_OC of 1.35 V. Finally, we fabricated all-perovskite tandem solar cells with above optimized WBG perovskite, and achieved a noteworthy PCE of 27.1% with outstanding photostability. This work presents a novel strategy to reduce the V_OC deficit in WBG perovskite solar cells, ultimately benefiting the advancement of high-performance perovskite-based tandem solar cells.