Organic semiconductors herald new opportunities for fabricating high-performance flexible and wearable optoelectronic devices owing to their intrinsic mechanical flexibility, excellent optical absorption, and cool-free operation. The photocurrent generation mechanisms are of multiple physical origins, including photoconductive, photovoltaic, and photogating effects, and the influence of individual effects on the device figures-of-merit is still not well understood. Here we fabricated a high-performance pentacene single-crystal transistor employing graphene electrodes and demonstrated the modulation from the photogating mechanism to the photoconduction effect by controlling gate bias. Control experiments indicate that the calculation based on transfer curves tends to overestimate the responsivity due to nearby trap states. Using a high frequency-modulated light signal to suppress the trapping process, we successfully measured its intrinsic -3 dB bandwidth of 75 kHz. Finally, high-resolution and UV-NIR high-speed imaging capability was demonstrated. Our work provides new guidelines for understanding the photophysical process and intrinsic performances of organic devices and also confirms the potential of organic single crystals in high-speed imaging applications.
Keywords: high-speed imaging; intrinsic response; organic crystal; pentacene; phototransistor.