Dissociation of charge transfer excitons at the donor–acceptor interface in bulk heterojunction organic solar cells

It is emphasized that the formation of charge transfer (CT) excitons in bulk heterojunction (BHJ) organic solar cells (OSCs) does not automatically lead to the dissociation of excitons and generation of charge carriers due to the built-in electric field created by the difference in the work functions of the electrodes. Like Frenkel excitons, CT excitons are also charge neutral excited entities and cannot be efficiently dissociated by such electric field. A condition of the dissociation of CT excitons is proposed and used to derive the rates of exciton dissociation in BHJ OSCs. Results are calculated and compared with experiments for the BHJ OSC of PTB7: PC71BM and found to agree very well qualitatively.