Charge‐Transfer Complexes and Their Role in Exciplex Emission and Near‐Infrared Photovoltaics

Charge transfer and interactions at organic heterojunctions (OHJs) are known to have critical influences on various properties of organic electronic devices. In this Research News article, a short review is given from the electronic viewpoint on how the local molecular interactions and interfacial energetics at P/N OHJs contribute to the recombination/dissociation of electron‐hole pairs. Very often, the P‐type materials donate electrons to the N‐type materials, giving rise to charge‐transfer complexes (CTCs) with a P δ+ –N δ− configuration. A recently observed opposite charge‐transfer direction in OHJs is also discussed (i.e., N‐type material donates electrons to P‐type material to form P δ− –N δ+ ). Recent studies on the electronic structures of CTC‐forming material pairs are also summarized. The formation of P δ− –N δ+ ‐type CTCs and their correlations with exciplex emission are examined. Furthermore, the potential applications of CTCs in NIR photovoltaic devices are reviewed.