B ← N Bridged Polymer Acceptors with 900 nm Absorption Edges Enabling High-Performance All-Polymer Solar Cells

Most of the high-performance polymer acceptors have a defect of unsatisfying light-harvesting ability, e.g., a moderate absorption coefficient in films (Amax < 1 × 105 cm–1) or limited spectra coverage with absorption edge (λedge) lower than 900 nm, severely hindering their further improvement of short-circuit current densities (JSC) and efficiencies. Particularly, for the current B ← N embedded polymers, all of the known acceptors have λedge's lower than 800 nm and JSC's lower than 15 mA/cm2. In this work, we present two B ← N bridged polymers named BN-V and BN-Me-V by copolymerizing vinyl with BNIDT and BNIDT-Me, respectively. The methyl (Me) groups are introduced to finely tune the energy levels and absorption spectra. For the Me-anchored polymer BN-Me-V, a promising λedge of 880 nm and a moderate Amax of 0.95 × 105 cm–1 are achieved. Interestingly, the Me-free polymer BN-V showed a red-shifted λedge of 900 nm and an enhanced Amax of 1.08 × 105 cm–1. Moreover, by selecting PTB1 (a copolymer of an ester-substituted 2,5-dibromothieno[3,4-b]thiophene and dialkoxyl benzodithiophene) as the donor polymer to prepare all-PSCs, a BN-V-based device affords a high JSC of 16.90 mA/cm2, which is the highest value among the JSC's of reported B ← N-type polymer acceptors. Finally, the efficiency of the BN-V-based device reaches 7.25%. This is the second report on the near-infrared polymer acceptor with 900 nm absorption edge that can afford high efficiencies beyond 7.00%.