Ultrahigh detectivity of near-infrared organic phototransistor assisted by additional electron trap sites in a dielectric layer†

The introduction of electron traps can effectively increase the photocurrent of a device since the photovoltaic-induced current of phototransistors is proportional to the turn-on voltage shift and the total number of trapped charges. However, high concentration of carrier trap sites in the active layer introduces strong current traps and promotes carrier recombination, which reduces the photocurrent of phototransistors, especially for narrow-band near-infrared photodetection. In this study, additional electronic traps were introduced into the dielectric layer of a phototransistor, demonstrating stable photoinduced charge traps for achieving a high photocurrent and photomultiplier effect without carrier quenching in the active layer. For an organic phototransistor with additional electronic traps in the dielectric layer, the response time remained basically unchanged after adding ZnO nanoparticles (ZnO-NPs) with a relatively low thickness (≤16 nm). The turn-on voltage shift (ΔV_on) increased from 19 V to 26 V, and the specific detectivity calculated by the dark current (shot noise, ) increased from 6.2 × 10¹⁵ Jones to 2.78 × 10¹⁶ Jones (@V_g = 3 V, 0.031 mW cm⁻² of 820 nm, where V_g is the gate voltage) as the additional electron traps were added into the organic phototransistor. The reported strategy has great optical and practical value for obtaining high-performance photodetectors with good overall performance.