Perovskite Surface Passivation Using Thiophene-Based Small Molecules for Efficient and Stable Solar Cells
Weihao Zhang, Min Yuan, Liang Han, Guohui Luo, Linfeng Zhang, Haiyan He, Ping Lin, Lingbo Xu, Xiaoping Wu, Xiaodong Zhu, Xuegong Yu, Peng Wang, Can Cui
Abstract
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.