Efficient and Stable Organic Solar Cells Enabled by Backbone Engineering of Nonconjugated Polymer Zwitterion Interlayers
Yongkang Jiang, Jing Tian, Wenxu Liu, Xin Chang, Yuxin Duan, Zuhao You, Xu Wang, Yao Liu
Abstract
Improving the efficiency and stability of fused-ring electron acceptor (FREA)-based organic solar cells (OSCs) by interface engineering is presently an emerging topic in the photovoltaic research field. Herein, we propose the design and efficient synthesis of four nonconjugated self-doped polymer zwitterions composed of the same electron-rich dopant but varied electron-deficient host fragments (perylene diimide and naphthalene diimide) and linkages (imidazolium and ammonium). Our results reveal that both their electrical properties and interfacial compatibility with active layers can be fine-tuned by structural modification, therefore impacting the power conversion efficiencies (PCEs) of the OSCs. The zwitterion combining perylene diimide and ammonium exhibits a more suitable energy level, higher conductivity, and more favorable film-forming ability with respect to others, which markedly modify the electrode/active layer interface, promote efficient charge extraction, and diminish charge recombination. This results in improved efficiency and stability of both binary and ternary FREA-based OSCs over a wide range of interlayer thickness with a maximum PCE value of 18.67% and high operational stability with T 80 > 800 h (the time scale for solar cell efficiency reaching 80% of the initial value). Our work provides an ingenious way to systematically optimize the molecular structures of nonconjugated polymer zwitterions toward more efficient and robust OSCs.