UV-induced oxygen removal for photostable, high-efficiency PTB7-Th:PC71BM photovoltaic cells

Abstract

Solution-processed ZnO sol–gel or nanoparticles are widely used as the electron-transporting layer (ETL) in optoelectronic devices. However, chemisorbed oxygen on the ZnO layer surface has been shown to be detrimental for the device performance as well as stability. Herein, we demonstrate that chemisorbed oxygen removal based on UV illumination of the ZnO surface layer under a nitrogen atmosphere can, simultaneously, improve the power conversion efficiency and photostability of PTB7-Th:PC71BM-based inverted polymer solar cells. By a systematic study of such a UV illumination procedure, we obtained optimal conditions where both the cell efficiency and stability were improved. We fabricated cells with a power conversion efficiency higher than 9.8% and with a T80 lifetime longer than 500 h, corresponding to about a 2.5-fold enhancement relative to non-UV-treated ZnO reference devices.