A Narrow‐Bandgap n‐Type Polymer with an Acceptor–Acceptor Backbone Enabling Efficient All‐Polymer Solar Cells

• DOI: 10.1002/adma.202004183
• Publication Date: 2020-09-21T09:30:29Z
• Authors: Huiliang Sun; Han Yu; Yongqiang Shi; Jianwei Yu; Zhongxiang Peng; Xianhe Zhang; Bin Liu; Junwei Wang; Ranbir Singh; Jaewon Lee; Yongchun Li; Zixiang Wei; Qiaogan Liao; Zhipeng Kan; Long Ye; He Yan; Feng Gao; Xugang Guo
• Keywords: Acceptor; Photocurrent; Electron acceptor; HOMO/LUMO

Narrow-bandgap polymer semiconductors are essential for advancing the development of organic solar cells. Here, a new narrow-bandgap acceptor L14, featuring an acceptor-acceptor (A-A) type backbone, is synthesized by copolymerizing dibrominated fused-ring electron (FREA) with distannylated bithiophene imide. Combining advantages both FREA and A-A polymer, L14 not only shows narrow bandgap high absorption coefficient, but also low-lying frontier molecular orbital (FMO) levels. Such FMO levels yield improved transfer character, unexpectedly, without sacrificing open-circuit voltage (Voc ), which attributed to small nonradiative recombination loss (Eloss,nr ) 0.22 eV. Benefiting from photocurrent along fill factor Voc , excellent efficiency 14.3% achieved, among highest values all-polymer cells (all-PSCs). The results demonstrate superiority polymers improving all-PSC performance pave way toward developing high-performance acceptors all-PSCs.