Surface Doping to Suppress Iodine Ion Migration for Stable FAPbI Perovskite Quantum Dot Solar Cells.

Formamidine lead iodide (FAPbI) quantum dots (QDs) have attracted great attention as a new generation of photovoltaic material due to their long carrier diffusion length, benign ambient stability, and light-harvesting ability. However, its large surface area with inherent thermodynamic instability and highly defective ionic termination are still major obstacles to fabricating high-performance devices. Herein, a metallic ion dopant is developed to post-treat FAPbI QDs immediately after their fabrication by using a metal-glutamate salt solution. Both experimental and theoretical results show that alkaline (earth) metal ions (Mg, Na, and K) in their glutamate salt can not only successfully substitute insulating long-chain ligands to form thinner ligand shells but inhibit the formation of iodine vacancies on the surface of QDs. As a result, the glutamate-Mg based solar cell exhibits a champion efficiency of 13.48%, and the other two solar cells treated by glutamate alkaline metal salts (Na and K) achieve photoelectrical conversion efficiencies of 13.26% and 11.88%, respectively, all of which are higher than of control cell with an efficiency of 11.58%. Therefore, this substantial progress provides intuitive cognition and guidance for the improvement of photoelectric performance and the commercial application of quantum dot solar cells.