Light-Induced Trap Reduction in Organic Shortwave Infrared Photodetectors

The distribution of trap states in an organic electronic device plays a critical role in their optoelectronic performance. These traps not only hinder the transport of photogenerated carriers but also cause severe recombination, thus deteriorating the overall photoresponse in the detector. Understanding and eliminating the traps in an organic photodetector is essential to promote and stabilize the response performances. This work examines the effects of trap distribution on the photoresponse performance in a shortwave infrared light detector, by interpreting charge transport dynamics and impedance characteristics. It is found that traps remaining in the device hinder the charge transport and collection in the detector because the traps can serve as recombination centers that deteriorate the photoresponse. The analysis of charge collection efficiency from current-voltage characteristics also validates this hypothesis. A dramatic trap reduction is realized by a proper exposure of the device to high-energy photons, which largely improves and stabilizes the photoresponse of the organic photodiode. It is also observed that the light-induced trap reduction is dependent on the wavelength and light intensity. The findings in this work reveal the fundamental mechanisms in the narrow-bandgap infrared sensing systems, paving the way for practical and stable infrared sensing application settings.