POS5-0063
Enhancing Organic Photodiodes Performance in the SWIR Region by Tuning Open/Closed-shell Characteristics
When and Where
Nov 30, -0001
12:00am - 12:00am
Presenter(s)
Seung-Gi Lee (Department of Chemical Engineering, POSTECH)
Co-Author(s)
Abstract
Organic photodiodes (OPDs) operating in the short-wave infrared (SWIR) region are attractive for sensing and imaging in biomedical diagnostics, non-destructive inspection, and autonomous driving due to their tunable spectral coverage, low cost, and compatibility with biocompatible and eye-safe illumination. However, their practical implementation remains challenged by insufficient long-wavelength absorption and inefficient exciton dissociation. To address this issue, we report novel thiadiazolo quinoxaline (TQ)-based push-pull-type copolymer donors (P1, P2, and P3) with different ratios of open/closed-shell blocks. These polymers demonstrate strong SWIR absorption, with absorption onsets reaching 1700, 1450, and 1680 nm, respectively, corresponding to ultralow optical band gaps of 0.73, 0.85, and 0.74 eV. We combined these molecules with the non-fullerene acceptor COTIC-4F in inverted bulk heterojunction (BHJ) OPDs. Optical and electrochemical characterization revealed narrow band gaps and large exciton binding energies. Device characterization demonstrated that enhanced open-shell character not only improves the external quantum efficiency (EQE) at longer wavelengths but also increases the dark current density, whereas greater closed-shell character suppresses dark current and promotes exciton dissociation at the expense of the long-wavelength EQE response. These findings reveal an intrinsic trade-off between long-wavelength photo response and dark current suppression and provide a promising molecular design approach for developing SWIR photodetection technology using organic semiconductors.
