Partial Charge Transfer Complexes for Highly Efficient 2 µm Light Detection

Achieving femtowatt sensitivity at room temperature remains an intractable challenge for organic shortwave infrared (SWIR) photodetectors (PDs), constraining their deployment in cutting-edge imaging and sensing modalities. The inherent deficiencies of contemporary organic SWIR PDs, including curtailed spectral absorption (> 1.0 µm), diminished external quantum efficiency (EQE), and suboptimal detectivity (D*), are inextricably tethered to trap-induced non-radiative recombination in narrow-bandgap organic semiconductors. To surmount these limitations, we employ the prototypical organic partial charge transfer (PCT) complex bis–1,3–dithiole–tetrachloro–1,4–benzoquinone (BT–TCBQ), which leverages partial charge localization and low-energy (< 0.7 eV) intermolecular electronic transitions. In this system, electrostatically tunable deep trap states (enabled by partial charge localization) amplify photo-gating-driven gain, while low-energy photoactivated ionic donor-acceptor pairs establish delocalized conduction pathways that suppress carrier scattering and Johnson-Nyquist noise. This synergistic mechanism enables room temperature, electrostatically gate-tunable operation with an EQE of ∼10³ %, D* of ∼10¹¹ Jones, and a 135 ms response at 2.0 µm under a low bias of 0.1 V. Our innovative strategic deployment of PCT complexes epitomizes a significant advance in monolithically organic SWIR optoelectronics, obviating the reliance on hybrid architectures while rivaling the performance of state-of-the-art inorganic counterparts.