A Quaternary Ammonium Salt with Strong Electron-Withdrawing Groups for Improving the Performance of CsPbI3 Quantum Dot Solar Cells

CsPbI3 quantum dots have been employed in solar cells, owing to their exceptional photovoltaic properties. However, the ligand exchange process occurring on the surface of these quantum dots is susceptible to environmental water and oxygen, resulting in phase transitions or even aggregation, ultimately degrading the solar cell performance. The application of a quaternary ammonium salt, specifically phenyltrimethylammonium iodide, possessing strong electron-withdrawing groups for the post-treatment of quantum dot films serves dual purposes: it not only occupies the A and X-site vacancies on the quantum dot surface generated by the desorption of oleic acid and oleylamine during the ligand exchange process but also forms a protective capping layer on the surface. This capping layer isolates the quantum dots from water and oxygen, thereby enhancing the film quality. Consequently, the power conversion efficiency of the control device, 9.29%, increases to 11.59% for the target solar cell with phenyltrimethylammonium iodide treatment. Moreover, the target solar cell remains above 93% of its initial efficiency value after a storage at 25–35% relative humidity and 35–40 °C in air for 14 days.