Efficient and Stable Carbon-Based Hole-Transport-Layer-Free CsPbI2Br Solar Cells by Adding Trace Amounts of Yttrium Acetate into the Photoactive Layer

CsPbI₂Br solar cells are a kind of important inorganic perovskite photovoltaic (PV) device that can serve as the top cells in a tandem configuration or semitransparent PV devices with balanced structural stability and light absorption. However, the issues relating to their power conversion efficiency (PCE) and long-term stability are still severely impeded by uncoordinated Pb²⁺ and migratable I^-. To effectively passivate the uncoordinated Pb²⁺ and meanwhile anchor the migratable I^-, herein, we propose a simple strategy by adding yttrium acetate (Y(Ac)₃) in the photoactive layer. A leading PCE of 15.53%, together with the notably improved stability and reduced current-voltage hysteresis, indicates the effectiveness of this additive strategy, as demonstrated in the carbon-based hole-transport-layer (HTL)-free CsPbI₂Br solar cells having a higher performance-to-cost ratio than their conventional counterparts because they abandon the usage of noble metal electrodes and the expensive organic HTLs that are also detrimental to the photoactive layer.