Incorporating Potassium Citrate to Improve the Performance of Tin-Lead Perovskite Solar Cells

Easy-to-form tin vacancies at the buried interface of tin-lead perovskites hinder the performance of low-bandgap perovskite solar cells (PSCs). Here, a synergistic strategy by incorporating potassium citrate (PC) into the poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) hole-transport layer to passivate the buried interface of Sn-Pb PSCs is reported. PC neutralizes the acidity of PEDOT:PSS and stabilizes the perovskite front surface, enhancing device stability. Citrate moieties coordinate with Sn²⁺ on the buried perovskite surface, preventing Sn²⁺ oxidation and suppressing defect formation. Additionally, potassium cations incorporate into Sn-Pb perovskites, enhancing crystallinity and passivating halide defects. The combined benefits enable efficient low-bandgap Sn-Pb PSCs with a power conversion efficiency of 22.7% and a high open-circuit voltage of 0.894 V. Using this method, 26.1% efficiency for all-perovskite tandem solar cells is demonstrated. These results emphasize the significance of buried interface passivation in developing efficient and stable Sn-Pb PSCs and all-perovskite tandem solar cells.