Surface Regulation via Carboxylate Polymer for Efficient and Stable CsPbI ₂ Br Perovskite Solar Cells

Abstract CsPbI ₂ Br perovskite solar cell (PSC) is a promising candidate for high‐efficiency single‐junction and tandem solar cells. However, due to the numerous surface defects of the CsPbI ₂ Br film and the mismatch of energy levels at the CsPbI ₂ Br/charge transport layer interface, the power conversion efficiency (PCE) of CsPbI ₂ Br PSC is still significantly lower than the theoretical limits. To alleviate those issues, in this work, a carboxylate‐based p‐type polymer, TTC‐Cl, is employed to modify the surface of CsPbI ₂ Br layer. TTC‐Cl can interact with uncoordinated Pb ²⁺ , thereby mitigating surficial defects of CsPbI ₂ Br film and reducing non‐radiative recombination losses. Furthermore, TTC‐Cl also improves the band properties of the CsPbI ₂ Br thin film surface, rendering it more p‐type, which facilitates hole transport. Consequently, the CsPbI ₂ Br PSCs with TTC‐Cl modification achieve a remarkable PCE of 17.81%, which is notably higher than that of counterpart without TTC‐Cl (15.87%). Moreover, CsPbI ₂ Br PSCs with TTC‐Cl modification also exhibit better stability. This work highlights the importance of surface regulation via carboxylate polymer for further enhancing the performance of CsPbI ₂ Br PSCs.