Universal Passivation Strategy for the Hole Transport Layer/Perovskite Interface via an Alkali Treatment for High‐Efficiency Perovskite Solar Cells

A passivation strategy for the perovskite/HTL interface is presented based on potassium acetate (K‐Ac). Since K‐Ac is soluble in both polar and nonpolar solvent, deposition of K‐Ac on top and bottom of perovskite is possible. With this advantage, the universality of potassium interfacial passivation at the HTL/perovskite interface applied to various configurations with various ranges of perovskite bandgap is reported. Regarding the p–i–n configuration, various materials characterizations reveal that a potassium passivation layer underneath perovskite modifies perovskite orientations, resulting in better charge transport and film properties. Furthermore, the potassium passivation layer shifts the valence band position of the HTL upward, which results in a better extraction of charges (holes) across the HTL/perovskite interface, thus improving the short‐circuit current density ( J sc ). The modification of the band alignment at the HTL/perovskite by the potassium interfacial passivation layer is confirmed in n–i–p devices with both WBG and CBG perovskites. Compared to reference solar cells without a passivation layer, an increase in J sc of approximately 1 mA cm −2 is observed in all cases, resulting in power conversion efficiencies of 19.42%, 20.06%, and 21.57% for WBG p–i–n, CBG p–i–n and n–i–p solar cells, respectively, demonstrating the wide applicability of the passivation strategy.