Enhanced Quasi-Fermi Level Splitting of Perovskite Solar Cells by Universal Dual-Functional Polymer

Perovskite solar cells (PSCs) have attracted extensive attention due to their higher power conversion efficiency (PCE) and simple fabrication process. However, the open-circuit voltage (V_OC) loss remains a significant impediment to enhance device performance. Here, a facile strategy to boost the V_OC to 95.5% of the Shockley-Queisser (S-Q) limit through the introduction of a universal multifunctional polymer additive is demonstrated. This additive effectively passivates the cation and anion defects simultaneously, thereby leading to the transformation from the strong n-type to weak n-type of perovskite films. Benefitting from the energy level alignment and the suppression of bulk non-radiative recombination, the quasi-Fermi level splitting (QFLS) is enhanced.  Consequently, the champion devices with 1.59 eV-based perovskite reach the highest V_OC value of 1.24 V and a PCE of 23.86%. Furthermore, this strategy boosts the V_OC by at least 0.07 V across five different perovskite systems, a PCE of 25.04% is achieved for 1.57 eV-based PSCs, and the corresponding module (14 cm²) also obtained a high PCE of 21.95%. This work provides an effective and universal strategy to promote the V_OC approach to the detailed balance theoretical limit.