Changing the π-bridge from thiophene to thieno[3,2-b]thiophene for D-π-A type polymer enables high performance fullerene-free organic solar cells
For photovoltaic polymers with D-π-A backbone, there are a great deal of D and A units, but the choice of π bridge is relatively limited and thiophene (T) is still the most effective one. Here we utilized two D-π-A polymers, J52-FS with thiophene as π bridge and PE2 with thieno[3,4-b]thiophene (TT) as π bridge, to combine with a low band-gap non-fullenere Y6, respectively. The photovoltaic cells based on PE2: Y6 can realize a PCE of 13.50%, which is obviously higher than the 10.58% of J52-FS: Y6 analog. Our works demonstrate that using TT as π-bridge is a simple and promising approach to construct efficient photovotaic polymers.