Project R-8535

Solution-processed bulk heterojunction organic cavities for near-infrared photodetection - rational combinations of novel donor and acceptor materials and dedicated solution processing for high performance devices (Research)

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 (EQE) in the spectral region of CT absorption can substantially be increased through the use of optical cavities, allowing narrow-band detection with substantial EQEs 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 high promises of this innovative concept, dedicated frontier research is required to optimize the device output and to elucidate its fundamental limits. A crucial aspect is the nanomorphology of the applied donor:acceptor blend, which is critically dependent on the processing conditions and inherent crystallization and mixing behavior of the components. In this project, advanced blend characterization of optimized material combinations will be combined with essential device feedback to unravel fundamental structure - solution processing - NIR photodetector relations.

01 January 2018 - 31 December 2021