Ultrahigh photosensitive organic phototransistors by photoelectric dual control

Abstract

Organic phototransistors (OPTs) simultaneously introduce photo-induced holes and electrons into the structure of organic field-effect transistors (OFETs). The memory effect of the minority carrier is the origin of the large dark current and slow response during the light on/off switching, which is detrimental to the OPT performance and cycling stability. In this research, we report a novel OPT working mode by photoelectric dual control. After each light switch, the dark current is erased by the gate voltage in depletion mode which remains unchanged during light off; the photocurrent increases by device converting to accumulation mode when the light is on. In this way, high performance OPTs have been obtained in an FBT-Th₄(1,4) : PC₆₁BM (5 : 1) composite film with the structure of Si/SiO₂/OTS/FBT-Th₄(1,4) : PC₆₁BM/Au electrodes, which shows a broad spectral response (maximum values at zero gate bias: R 1.2 × 10⁵ A W⁻¹, gain 3.7 × 10⁵ and D* 3.18 × 10¹⁶ Jones) from 410 to 740 nm (calculated from the transfer curve). The best performance with photoelectric dual control under 0.0031 mW cm⁻²@405 nm is achieved with an on/off current ratio of 1.0 × 10⁶, response 1.6 × 10⁴ A W⁻¹, gain 5.0 × 10⁴, spectral detectivity 2.3 × 10¹⁷ Jones and response time sub-40 ms, which makes the phototransistor a very promising component for light sensing applications.