Ultralow dark current in near-infrared organic photodetector via crosslinked conjugated polyelectrolyte hole-transporting layer

Organic photodetectors (OPDs) are of great interest for detecting near-infrared (NIR) and shortwave-infrared (SWIR) light due to their excellent photosensing capabilities and cost effectiveness. Hereby, we explore the use of a (3-glycidyloxypropyl)trimethoxysilane crosslinker in a conjugated polyelectrolyte (CPE) hole-transporting layer (HTL), which effectively boosts the stability and processability of the CPE as well as the sensitivity of the devices. We apply two rules for optimizing HTLs to reduce the dark current: conductivity/morphology regulation (via added crosslinker) and energy band alignment between the active layer and HTL (via molecular design), which enable a dark current density (Jd) of ∼1 nA cm−2 at −5 V for OPDs with sensitivity at λ > 1,000 nm. Intriguingly, we found that the thermal activation energy of Jd for the device with the champion condition is slightly lower than the blend's effective band gap of the active layer. This observation might open another perspective on the factors influencing Jd in NIR-SWIR OPDs.