We assembled a ternary blend bulk heterojunction polymer solar cell (PSCs) containing P3HT (donor) and PC61BM (acceptor) incorporated with a dihexyl-quaterthiophene (DH4T) small molecule oligomer as a third component. By optimizing the contents of DH4T, we increased the power conversion efficiency of ternary P3HT:DH4T:PC61BM PSCs to 4.17% from 3.44% of binary P3HT:PC61BM PSCs under AM 1.5 G of 100 mW/cm2 intensity. The major improvement is from the increase of the short circuit current and fill factor that is due to the increased light absorption at short wavelength, the balanced charge carrier transportation and the enhanced hole evacuation by a DH4T-enriched layer at the anode interface. In this work, we demonstrate that the efficiency of the PSCs can be enhanced by using low-bandgap conjugated polymer and its oligomer as donors and fullerene derivatives as acceptors.
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