Enhanced Electric Field Minimizing Quasi‐Fermi Level Splitting Deficit for High‐Performance Tin‐Lead Perovskite Solar Cells

Abstract The quasi‐Fermi level splitting (QFLS) deficit caused by the non‐radiative recombination at the interface of perovskite/electron transport layer (ETL) can lead to severe open‐circuit voltage (V_OC) loss and thus decreases the efficiency of perovskite solar cells (PSCs), however, has received limited attention in inverted tin‐lead PSCs. Herein, the strategy of constructing an extra‐electric field is presented by introducing ferroelectric polymer dipoles (FPD)‐β‐poly(1,1‐difluoroethylene)‐to suppress the QFLS deficit. The directional polarization of FPD can enhance the built‐in electric field (BEF) and thus promote the charge transfer at the perovskite/ETL interface, which effectively suppresses non‐radiative recombination. Furthermore, the incorporation of FPD facilitates high‐quality crystallization of perovskite and reduces the surface energetic disorder. Therefore, the QFLS deficit in the perovskite/ETL half‐stacked device is reduced from 62 to 27 meV after incorporating FPD, and the optimized device achieves an efficiency of 23.44% with a high V_OC of 0.88 V. Additionally, the addition of FPD increases the activation energy for ion migration, which can reduce the effect of ion migration on the long‐term stability of the device. Consequently, the FPD‐incorporated device retains 88% of the initial efficiency after 1100 h of continuous illumination at the maximum power point (MPP).