Intermolecular charge transfer (CT) states at the interface between electron-donating and electron-accepting (A) materials in organic thin films are characterized by absorption and emission bands within the optical gap of the interfacing materials. In this contribution, we will discuss the fundamental properties of CT states and link them to organic solar cell and light emitting diode performance. Furthermore, we introduce a new device concept, using an optical cavity resonance effect to boost CT absorption at photon energies below the optical gap of both donor and acceptor, enabling sensitive narrow-band, near infrared photo-detection.
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