Dual Forster resonance energy transfer and morphology control to boost the power conversion efficiency of all-polymer OPVs

Broadening the absorption spectrum and efficiently harvesting photogenerated excitons are crucial tasks to realize high-efficiency polymer solar cells (PSCs). Recently, ternary PSCs with complementary absorptions into a single junction device have been emerging as a promising strategy to enhance the absorption of binary PSCs. However, the effect of ternary PSCs critically depends on the location of the third component according to different principles. Due to the hard control of the third component location, only limited high-performance ternary systems have been demonstrated previously. Here, we develop a new concept of dual Forster resonance energy transfer (dual-FRET), in which the third component acts as an energy donor and the donor and acceptor act as an energy acceptor. Thus, exciton energy of the third component could transfer energy to both the donor and the acceptor through the FRET principle. Consequently, the third component should only be dispersed uniformly in the binary film regardless of its location. Using this concept, the performance of ternary PSCs, i.e., PTB7-Th (donor)/P(NDI2OD-T2) (accepter)/PF12TBT (the third component), reaches 6.07%, more than about 30% compared to the corresponding binary PSCs (4.70%). Our work provides a novel way for designing ternary structures to boost the efficiency of PSCs.