ORGS4-0098
From Charge Collection Narrowing to Photomultiplication: Unconventional Strategies to Enhance NIR/SWIR Detection in Organic Photodetectors
Topic
GS4. Graduate Student Oral Session IV: Polymers for Electronics, Photonics, and Energy
When and Where
Sep 28, 2026
15:48 - 16:00
Room 104
Session Chairs
Hobeom KIM
Giwon LEE
Hyeong Jun KIM
Presenter(s)
Matilde Brunetta (Imperial College London)
Co-Author(s)
Abstract
Charge collection narrowing (CCN) and photomultiplication (PM) are two promising strategies employed in organic photodetectors (OPDs) to assist near-infrared (NIR) and short-wave infrared (SWIR) detection. The two approaches are based on completely different processes, with CCN being imposed via thick bulk heterojunctions (BHJs) allowing only sub-bandgap photons to be extracted, resulting in spectrally selective OPDs without need for input filtering. PM effect, instead, is a method used to achieve external quantum efficiencies (EQEs) above unity by adopting unbalanced donor:acceptor ratios in the BHJ and exploiting trap-assisted charge tunnelling injection at higher reverse bias. Despite both being already established practices in literature, their mechanism is still under discussion leaving plenty of room for exploration. Here, we present a novel low bandgap random copolymer (ranDPP-2TBT) used as a donor material in OPDs. RanDPP-2TBT was blended with non-fullerene (NFA) acceptor IEICO-4F to obtain CCN OPDs with a specific detectivity of 1011 Jones at -2 V at 916 nm and a spectral response window as narrow as 68 nm (full-width-at-half-maximum). This was achieved with an active layer thickness of only 1 μm, among the lowest in literature for CCN OPDs. Finally, we demonstrate the first application of a CCN-derived OPD as a real-time contactless heart rate monitoring device based on photoplethysmography (PPG). Secondly, we introduce PM-OPDs utilizing an equal donor:acceptor ratio in the BHJ, changing the common understanding of PM-OPDs. NIR polymer TQ-3T was used with NFA Y6. PM-OPDs with EQE of above 1100% at 840 nm and 31% at 1100 nm at -10 V, and fast response times of 73 µs were achieved. We also demonstrate ultrathin (<3 µm) flexible PM-OPDs with a stable dark current density after 1000 bending cycles. Finally, we demonstrate an application of the PM-OPD as a flexible and pulse oximeter and large-area image sensor for accurate vein recognition.
