Perovskite Surface Passivation Using Thiophene-Based Small Molecules for Efficient and Stable Solar Cells

Thesuppression of perovskite surface defect recombination is verycritical in obtaining high-efficiency perovskite solar cells (PSCs).Ammonium salts with long carbon chains or forming two-dimensional(2D) perovskites are usually used to passivate defects. However, theymight limit carrier extraction or transport due to the electricalinsulation of long-chain organic ligands. Herein, we propose a smallmolecule of thiophene-2-acetamide (TAA) to passivate surface defectsof a methylammonium lead iodide (MAPbI(3), where MA is methylammonium)perovskite film. The results suggest that the S atom of thiophenesuppresses Pb-0 defects and the -C UO grouppassivates the uncoordinated Pb2+ by forming chemical bondswith Pb2+. The -NH2 group further enhancesthe interaction between TAA and perovskite surface defects by forminghydrogen bonds with I-. Moreover, carrier extractionis promoted significantly from the perovskite film to the hole-transportlayer. The incorporation of the TAA additive is found to enhance thecrystallization of films via a strong interaction between the -C UOgroup and Pb2+ of the perovskite precursors. The synergisticeffect of surface passivation and enhanced crystallization has beensuccessfully demonstrated in the champion MAPbI(3) PSCs,resulting in a significantly enhanced conversion efficiency from 18.35%to 20.62%. Notably, the device stability under 1-sun illuminationand high humidity (& SIM;85%) in air has significantly been improved.