Tuning Molecular Interaction in Polymer Solar Cells via a Multifunctional Discotic Component to Enhance Photovoltaic Response

A donor-acceptor (D-A)-type discotic organic material (TP-2-PIE), having a self-organization ability, is selected to be the third component blending with poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene-co-3-fluorothieno [3,4-b]-thiophene-2-carboxylate] (PTB7-Th): [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) in ternary bulk-heterojunction polymer solar cells. The complementary absorption and energy transfer between TP-2-PIE and PTB7-Th contributes to the enhancement in photocurrent generation, improving the short-circuit current. In addition, TP-2-PIE alters the molecular interaction leading to an enhanced phase separation, which promotes carrier transport with a good balance and minimizes the density of trap states simultaneously. In this way, the overall photovoltaic performances are markedly enhanced at an optimal condition of 10 wt% TP-2-PIE in donors with a 12.6% efficiency increase. Current understanding on the functionality of this third component in ternary solar cells may be able to guide future device development.