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.
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