Benzo[1,2-b:4,5-b′]difuran Based Polymer Donor for High-Efficiency (>16%) and Stable Organic Solar Cells

Molecular design of polymer donors is of vital importance for obtaining high-performance organic solar cells (OSCs). At present, much of the important progress in power conversion efficiencies (PCEs) achieved for OSCs has been associated with the benzodithiophene (BDT)-based polymers, while the highest PCE of benzo[1,2-b:4,5-b′]difuran (BDF) polymer-based OSCs only reaches 14.0%. Here, a polymer donor named PBDF-NS is designed and synthesized by using naphthalene-substituted benzo[1,2-b:4,5-b′]difuran as the electron-sufficient units and fluorinated benzotriazole (BTz) as the electron-deficient units. PBDF-NS possesses a low-lying HOMO level of −5.44 eV and a wide bandgap of 1.87 eV. When using LC301 as the acceptor, PBDF-NS-based OSC exhibits an excellent PCE of 15.24%. Moreover, the ternary and all-polymer devices based on PBDF-NS both achieve a higher PCE over 16%, which represents the highest efficiency values reported for BDF polymer-based OSCs in the literature thus far. Meanwhile, the binary and ternary devices all display excellent storage and light-soaking stabilities. The results demonstrate that by rational molecular design, BDF-based copolymers can be comparable to or even surpass the performance of BDT-based counterparts and also show great potential for realizing high-efficiency all-polymer solar cells.