High-performance conjugated terpolymer-based organic bulk heterojunction solar cells

Recently, conjugated terpolymers comprising three components have attracted tremendous attention. However, quite a few examples of high-performance terpolymers have been reported. We present here two novel terpolymers named PtDDA and PtDAA, in which bithiophene (BT) and benzo[1,2-c:4,5-c′]dithiophene-4,8-dione (T1) were chosen as the donor and acceptor units, respectively. Thieno[3,2-b]thiophene (TT) and thiazolo[5,4-d]thiazole (TTz) were used as the third component. It is interesting to find that the PtDDA terpolymer shows a typical D1-D2-D1-A1 structure while PtDAA shows a D1-A1-D1-A2 structure. Without using additives or post-annealing processes, PtDAA-based solar cells show a high PCE of 8.1%, with an unprecedented fill factor (FF) of 0.74, which is much higher than those of PtDDA-based devices (PCE = 3.4%, FF = 0.55). The high efficiency of 8.1% is one of the highest values reported so far for organic solar cells based on conjugated terpolymers. The high performance is mainly ascribed to the efficient carrier transport in the PtDAA:PC₇₁BM active layer, high crystallinity of PtDAA, and high domain purity. The results suggest that constructing conjugated terpolymers with one donor and two acceptor units is an effective strategy for designing high-performance solar cell materials.