Multifunctional Bridging Molecule 4-Guanidinobutyric Acid-Induced Dual-Interface Passivation Strategy in MAPbI₃ Perovskite Solar Cells

Well-performed perovskite solar cells are usually equipped with a SnO2 electron transport layer. Aiming at the complicated defects at the SnO2 electron transport layer and perovskite interface, a bridging modification strategy is proposed using 4-guanidinobutyric acid, which consists of dual-terminal donor groups. The theoretical calculation results reveal that 4-guanidinobutyric acid can establish robust interaction between SnO2 electron transport layer and perovskite, using one side of donor groups to mitigate the uncoordinated Sn4+, oxygen vacancies, and dangling hydroxyl defects on SnO2 surface, and using the other side of donor group to reduce the uncoordinated Pb2+ defects in perovskite. Meanwhile, the H–N bonds in −NH2 can anchor uncoordinated I– through I···H–N interaction, inactivating uncoordinated I– defects. The interaction between 4-guanidinobutyric acid and perovskite promotes the crystallization procedure of the perovskite layer, reducing the roughness of the perovskite film. Further investigations demonstrate that cross-linking contributes to better energy level alignment and facilitates efficient interfacial carrier transport. As a result, the nonradiative recombination at the buried interface gets reduced. With 4-guanidinobutyric acid interface bridging, the device’s efficiency improves from 18.85 to 20.78%. This work exhibits an effective bridging agent to modulate the SnO2/perovskite interface.