Dual Defect Passivation at the Buried Interface for Printable Mesoscopic Perovskite Solar Cells with Reduced Open‐Circuit Voltage Loss

Abstract Numerous defects exist at the buried interface between the perovskite and adjacent electron transport layers in perovskite solar cells, resulting in severe non‐radiative recombination and excessive open‐circuit voltage (V_OC) loss. Herein, a dual defect passivation strategy utilizing guanidine sulfate (GUA₂SO₄) as an interface modifier is first reported. On the one hand, the SO₄²⁻ preferentially interacts with Pb‐related defects, generating water‐insoluble lead oxysalts complexes. Additionally, GUA⁺ diffuses into the perovskite and induces the formation of low‐dimensional perovskite. These reactions effectively suppress trap states at the buried interface and perovskite boundaries in printable mesoscopic perovskite solar cells (p‐MPSCs), thus increasing the carrier lifetime. Meanwhile, GUA₂SO₄ optimizes the interface energy band alignment, thus accelerating the charge extraction and transfer at the buried interface. This synergistic effect of trap passivation and interface energy band alignment modulation is strongly demonstrated by an increase in average V_OC of 70 mV and the power conversion efficiency improvement from 17.51% to 18.70%. This work provides a novel approach to efficiently improve the performance of p‐MPSCs through dual‐targeted defect passivation at the buried interface.