Surface Regulation via Carboxylate Polymer for Efficient and Stable CsPbI₂Br Perovskite Solar Cells

CsPbI₂Br 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 CsPbI₂Br film and the mismatch of energy levels at the CsPbI₂Br/charge transport layer interface, the power conversion efficiency (PCE) of CsPbI₂Br 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 CsPbI₂Br layer. TTC-Cl can interact with uncoordinated Pb²⁺, thereby mitigating surficial defects of CsPbI₂Br film and reducing non-radiative recombination losses. Furthermore, TTC-Cl also improves the band properties of the CsPbI₂Br thin film surface, rendering it more p-type, which facilitates hole transport. Consequently, the CsPbI₂Br 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, CsPbI₂Br 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 CsPbI₂Br PSCs.