Electronic Structure and Properties of Organic Bulk‐Heterojunction Interfaces

The electronic structure and physical mechanisms of carrier generation and transport in the organic bulk heterojunction are reviewed. The electronic structure describes the bands and band‐tail states, the band alignment at the bulk‐heterojunction interface, and the overall density‐of‐states model. The different electronic character of excitons and mobile charge is discussed, the former being highly molecular and the latter more delocalized. Dissociation of the exciton via the charge‐transfer (CT) states is attributed to weak binding of the CT state arising from charge delocalization. Carrier transport and charge collection is strongly influenced by the presence of localized band‐tail states. Recombination is attributed primarily to transitions from mobile carriers to band‐tail or deep trap states.