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

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).