Ammonium Additive Engineering in Antisolvents for Improving Perovskite/Charge-Transport-Layer Interfaces toward Efficient Lead–Tin Alloyed Perovskite Solar Cells

Although significant advancements have been achieved in lead–tin (Pb–Sn) alloyed perovskite solar cells (PSCs), their power conversion efficiency (PCE) remains inferior to that of their Pb-based counterparts, primarily due to higher open-circuit voltage ( V oc ) losses and lower fill factors (FFs). Herein, we report both perovskite top and bottom interfacial improvements by incorporating a facile fluorophenylethylammonium iodide (p-FPEAI)/ethyl acetate (EA) solution during the film crystal growth. Based on the analysis of perovskite crystallization, film growth, and strain relaxation, the mechanisms behind these interfacial improvements have been well understood. Furthermore, p-FPEAI could reduce the defect density and nonradiative recombination losses, thus attributing to the improved V oc and FF. Finally, the treated device achieved a PCE of 20.14% with a V oc of up to 0.84 V, which is among the highest reported values so far for Pb–Sn alloyed PSCs without additional precursor additives. In addition, the unencapsulated p-FPEAI-treated device maintained its initial efficiency of approximately 92% after being kept in a nitrogen atmosphere for 1 month, in contrast to the control device which retained only 30% of its initial value. Our findings provide a comprehension for understanding the effect of bulky cations as antisolvents on fabricating highly efficient Pb–Sn alloyed perovskite solar cells.