Multispectral Organic Photodetectors

Organic photodetectors (OPDs) are a promising alternative optical detecting technology to conventional wafer-based inorganic counterparts, because the optical and electric properties of the organic semiconductor materials can be tailored accordingly. They offer additional advantages such as having a solution-processable fabrication process, which also leads to significant cost benefits, thereby creating next-generation solutionprocessable, flexible, and low-cost photodetectors. In general, the spectral responses of
the photodetectors are determined by the absorption of the active materials and optical profile in the devices. Single-band OPDs optimized for photodetection at the specific spectral ranges have been reported. However, the reports on OPDs for multispectral
detection are rather rare. It is a great challenge to achieve high-performance multispectral OPDs.

This project proposes to develop a novel filter free multispectral OPD using a back-toback stacked photodiode/photomultiplication (photodiode/PM) double heterojunction
structure. The front junction responds to short-wavelength (visible) light, whereas the rear junction responds to near-infrared (NIR) light. The use of a back-to-back stacked photodiode/PM double heterojunction in the OPD will improve NIR responsivity through PM effect, due to the trap-assisted charge injection at the PM-type NIR absorber/cathode interface under a reverse bias. The photodiode/PM double heterojunction OPD allows a multispectral detection that is controlled by the polarity of a bias voltage applied between the two contacts in the device. The OPD will also exhibit
a broadband photoresponse when it is operated using a 50% duty-cycled square-wave voltage supply. The resulting technology will enable high-performance multispectral OPDs for applications in areas such as security monitoring, artificial intelligence, highresolution image sensing, Internet of Things, and optical communications.