Metallic Fabry-Pérot Cavity-Enhanced "Pseudo-Charge Transfer" Absorption for Efficient Narrowband Short-Wave Infrared Photodetection.

Narrowband short-wave infrared (SWIR) organic photodetectors, combining wavelength-specific detection with the inherent advantages of organic semiconductors, are important candidates for many applications like medical diagnostics, industrial sorting, and environmental monitoring. However, previously reported spectral-narrowing strategies often compromise device performance through structural complexity and intrinsic limitations of charge-transfer (CT) absorption, even when coupled with strong cavity device architectures. To address this, a pseudo-charge-transfer state is engineered by doping an ultra-narrow bandgap third component, simultaneously optimizing electrode processing to minimize parasitic absorption and interface energetic barriers. This co-design approach yields spectrally selective photodetectors with an EQE exceeding 40% at zero-bias at 1020 nm, a FWHM of < 60 nm, a detectivity > 3 × 1013 Jones, and an over 140dB dynamic range, while maintaining flexibility. PET-based devices show <5% performance degradation after 3000 bending cycles. This work establishes a general design paradigm for organic narrowband photodetectors that combines laboratory-scale performance with practical manufacturability for wearable and large-area SWIR applications.