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

The suppression of perovskite surface defect recombination is very critical 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, they might limit carrier extraction or transport due to the electrical insulation of long-chain organic ligands. Herein, we propose a small molecule of thiophene-2-acetamide (TAA) to passivate surface defects of a methylammonium lead iodide (MAPbI 3, where MA is methylammonium) perovskite film. The results suggest that the S atom of thiophene suppresses Pb 0 defects and the −C═O group passivates the uncoordinated Pb 2+ by forming chemical bonds with Pb 2+ . The −NH 2 group further enhances the interaction between TAA and perovskite surface defects by forming hydrogen bonds with I – . Moreover, carrier extraction is promoted significantly from the perovskite film to the hole-transport layer. The incorporation of the TAA additive is found to enhance the crystallization of films via a strong interaction between the −C═O group and Pb 2+ of the perovskite precursors. The synergistic effect of surface passivation and enhanced crystallization has been successfully 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 illumination and high humidity (∼85%) in air has significantly been improved.