Differential organic photodetectors with nanograting-defined spectral responsivity

Optoelectronic sensing devices based on organic semiconductor materials are a promising technology due to their integrability in several sensing platforms and applications. Many sensing applications require narrowband detection, and suppression of background noise is desired. We introduce a differential readout concept using organic photodetectors (OPDs) that share an identical material stack but incorporate different nanograting periods to couple light resonantly into guided modes at distinct wavelengths. We fabricate CuPc/C₆₀ OPDs with grating periods Λ₁ = 350 nm and Λ₂ = 400 nm, targeting resonances at wavelengths λ₁ = 550 nm and λ₂ = 600 nm, respectively, and we measure their optical transmission and spectral photocurrent. Under tunable laser excitation in the visible, we observe guided-mode resonances that translate into narrowband responsivity enhancements at the designed wavelengths. Differential and subtractive analyses between the two OPDs isolate the nanostructure-induced response and show responsivity enhancements up to 40% at resonance. Under white-light and selective LED spectra, we quantify photoconversion efficiency and demonstrate that narrowband sensitivity is enhanced for signals near resonance.