Crystalline Medium-Bandgap Light-Harvesting Donor Material Based on β-Naphthalene Asymmetric-Modified Benzodithiophene Moiety toward Efficient Polymer Solar Cells

In this paper, we reported a crystalline p-type medium-bandgap conjugated D–A polymer asy-PBDBTN based on a symmetry-breaking-modified BDT moiety to combine the advantages of both one-dimension (1D) and two-dimension (2D) symmetric BDTs. Polymer asy-PBDBTN is a highly efficient light-harvesting donor material. Single BHJ PSCs exhibit PCE of 8.88% with PC₇₁BM as acceptor. Also, PCE values of 10.50% are achieved with the use of ITIC as an acceptor to couple asy-PBDBTN with V_OC of 0.942 V, J_SC of 16.81 mA cm^–2, and FF of 0.663. It is worth noting that lower energy loss is obtained in fullerene-free-based PSCs, which is essential to overcome the trade-off between V_OC and J_SC and boost these two parameters simultaneously for high photovoltaic performance. The combination process of additive and thermal annealing is critical to enhance and retain the π–π stacking behavior of donor and fullerene-free acceptor; as a result, the trap-assisted recombination was greatly suppressed. This work demonstrates a great prospect for the construction of the symmetry-breaking BDT-based D–A conjugated polymers toward high-performance PSCs, especially with fullerene-free acceptor material.