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.