We report the fabrication of a photoresponsive organic field-effect transistor (OFET) based on a stable, n-type organic semiconductor (F 16 CuPc) and low-temperature processable polymer gate dielectric. The device exhibited a photoswitching speed of much less than 10 ms and a photosensitivity of 1.5 mA/W at low optical power. Under illumination, the device produced a current gain (I light /I dark ) of 22 at V G ) 4 V. The drain current increased gradually with an increase in the illumination intensity, resulting in typical output FET characteristics. The multifunctions (photodetection, photoswitching, signal amplification) achieved by the single device can ensure very promising material for future optoelectronic applications.

Highly stable, reproducible, photosensitive organic field-effect transistors based on an n-type organic material, copper hexadecafluorophthalocyanine, and two different polymeric gate dielectrics has been reported and their performances have been compared by evaluating the surface/interface properties. The devices produced a maximum photocurrent gain (I(light)/I(dark)) of 79 at V(G) = 7 V and showed the potentiality as multifunctional optoelectronic switching applications depending upon the external pulses. The switching time of the transistor upon irradiation of light pulse, i.e., the photoswitching time of the device, was measured to be approximately 10 ms. On the basis of optical or combination of optical and electrical pulses, the electronic/optoelectronic properties of the device can be tuned efficiently. The multifunctions achieved by the single device can ensure very promising material for high density RAM and other optoelectronic applications. Furthermore, as the device geometry in the present work is not limited to rigid substrate only, it will lead to the development of flexible organic optoelectronic switch compatible with plastic substrates.

High quality, single crystalline, ordered arrays of a p-conjugated organic molecule, N,N 0 -dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C 8 ), were grown by solution processing and used to fabricate a low-cost, high-performance organic phototransistor (OPT). The single crystalline nature of the microstructure was investigated using 2D-GIXD measurement. The organic field-effect transistor fabricated using periodic arrays of elongated crystals exhibited a photoresponsivity (P) of ca. 1 A W À1 and a photo to dark current ratio (I on /I off ) of 2.5 Â 10 3 at V G ¼ 12 V and a maximum P of ca. 7 A W À1 at the high gate bias regime (V G ¼ 50 V) with an optical power of ca. 7.5 mW cm À2 . With polymeric gate dielectric, the OPT exhibited very stable n-type characteristics both in the dark and under light illumination and showed reproducible photo-switching behavior. The dependence of the photocurrent on the gate/drain voltage and on illumination intensity provided an effective way to control the number of photo-carriers generated in the active material, enabling the precise tuning of the device's performance. Performance comparison between OPTs with ordered crystal arrays and thin films of PTCDI-C 8 confirmed that the material's intrinsic properties were better realized in the crystalline device, presumably because of higher charge carrier mobility and better charge transport capability. This one-step, solution-based, self-assembly fabrication of multifunctional (photodetection, photoswitching, signal amplification) optoelectronic devices has potential to aid the development of organic semiconductors with high-quality micro/nanostructures for large-scale application and lowcost optoelectronic devices.

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