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 (A(max)< 1 x 10(5) cm(-1)) or limited spectra coverage with absorption edge (lambda(edge)) lower than 900 nm, severely hindering their further improvement of shortcircuit current densities (J(sc)) and efficiencies. Particularly, for the current B <- N embedded polymers, all of the known acceptors have lambda(edge)'s lower than 800 nm and J(SC)'s lower than 15 mA/cm(2). 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 lambda(edge) of 880 nm and a moderate A(max) of 0.95 X 10(5) cm(-1) are achieved. Interestingly, the Me-free polymer BN-V showed a red-shifted lambda(edge) of 900 nm and an enhanced A(max) of 1.08 X 10(5) 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 J(SC) of 16.90 mA/cm(2), which is the highest value among the J(SC)'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%.