Revealing optically induced dipole-dipole interaction effects on charge dissociation at donor:acceptor interfaces in organic solar cells under device-operating condition

Abstract

Organic materials normally have low dielectric constants and are often formed with high electron-hole binding energy, which are detrimental to the generation of photovoltaic actions in solution-processing thin-film solar cells. Here, we show that optically induced dipole-dipole interaction can largely decrease the electron-hole binding energy at donor:acceptor (D:A) based on the PTB7:PCBM bulk-heterojunctions. Our experimental measurements combine (i) double-beam 325nm and 532nm excitations to establish dipole-dipole interaction by selectively exciting the intramolecular charge-transfer donor and optically polarizable acceptor and (ii) magneto-photocurrent to monitor the electron-hole binding energy through charge dissociation at D:A interfaces. We find that the electron-hole binding energy at D:A interfaces can be significantly decreased when the dipole-dipole interaction is optically established in PTB7:PCBM solar cells. Furthermore, the dipole-dipole interaction forms a drifting field to facilitate charge transport, and consequently enhancing the Voc and FF in developing photovoltaic actions in organic solar cells.