Organic cavity photodetectors

Blending organic electron donors and acceptors yields intermolecular charge transfer (CT) states with additional optical transitions below their optical gaps. In organic photovoltaics, such CT states play a crucial role and they limit the operating voltage. Due to its extremely weak nature, direct intermolecular CT absorption often remains undetected and unused for photocurrent generation. However, the negligible external quantum efficiency in the spectral region of CT absorption can substantially be increased through the use of optical cavities, allowing narrow-band detection with substantial quantum efficiencies and resonance wavelengths extending into the near-infrared (NIR). The broad spectral tunability via simple variation of the cavity thickness makes this novel, flexible, and potentially visibly transparent device principle highly suitable for integrated low-cost (spectroscopic) NIR photodetection. Despite the promises of this innovative concept, dedicated strategic research is required to further optimize the device output and elucidate its limitations.