This work demonstrates an effective graded bulk-heterojunction (G-BHJ) strategy using nonhalogenated solvent sequential deposition for non-fullerene acceptor (NFA) organic solar cells (OSCs). Spin-coated G-BHJ OSCs achieved a 17.48% power conversion efficiency (PCE), with thick OSCs maintaining high PCEs (16.25% for 300 nm, 14.37% for 500 nm). Depth-profiling X-ray photoelectron spectroscopy (DP-XPS) and angle-dependent grazing incidence X-ray diffraction (GI-XRD) revealed beneficial polymer/NFA composition and crystallinity gradients. Furthermore, a blade-coated G-BHJ OSC achieved a record 16.77% PCE using nonhalogenated solvents in open air, showcasing the potential for efficient and eco-friendly OSCs.

Ying Zhang, Kuan Liu, Jiaming Huang, Xinxin Xia, Jiupeng Cao, Guangming Zhao, Patrick W. K. Fong, Ye Zhu, Feng Yan, Yang Yang, Xinhui Lu, Gang Li