Synergistic passivation by alkali metal and halogenoid ions for high efficiency HTM-free carbon-based CsPbI2Br solar cells

Abstract Hole transport material (HTM)-free carbon-based all-inorganic perovskite solar cells (C-PSCs) possess excellent thermal stability and low cost, which promise an alternative to replace the conventional organic–inorganic hybrid PSCs. The additive method is an effective approach to enhance the performance of PSCs by improving the quality of perovskite films. Herein, the synergistic passivation strategy of alkali metal and halogenoid ions in NaSCN additive is adopted to suppress nonradiative recombination in CsPbI2Br films. The Na+ is incorporated at the A-site of CsPbI2Br cell that enhances the I− diffusion barrier energy from 0.229 eV to 0.401 eV, suggesting suppressed iodide vacancy. Moreover, the SCN− plays a role in regulating the crystal growth dynamics during the CsPbI2Br film formation process, reducing defect density. This synergistic passivation strategy effectively improves the perovskite film quality, and increases the recombination resistance and the carrier extraction efficiency of CsPbI2Br films, therefore reducing nonradiative recombination loss in the final device. The assembled HTM-free carbon-based all-inorganic CsPbI2Br perovskite solar cells present a champion PCE of 14.63% (VOC = 1.267 V, JSC = 14.31 mA/cm2, fill factor (FF) = 0.807), which is among the best performances in the carbon-based all-inorganic perovskite solar cells.