Magneto-optical investigations on the formation and dissociation of intermolecular charge-transfer complexes at donor-acceptor interfaces in bulk-heterojunction organic solar cells.

The electron-hole pairs can be formed in intermolecular charge-transfer (CT) states between two adjacent molecules due to Coulomb interaction in organic semiconducting materials. In general, the exciton dissociation can experience the intermediate states: intermolecular CT states at the donor-acceptor interfaces to generate a photocurrent in organic solar cells. This article reports the magneto-optical studies on intermolecular CT states in the generation of photocurrent by using magnetic field effects of photocurrent (MFE(PC)) and light-assisted dielectric response (LADR). The MFE(PC) and LADR studies reveal that internal electrical drifting and local Coulomb interaction can largely change the formation and dissociation of CT states by changing internal charge-transport channels and local Coulomb interaction through morphological development upon thermal annealing. Therefore, the MFE(PC) and LADR can be used as effective magneto-optical tools to investigate charge recombination, separation, and transport in organic solar cells.