Organic phototransistors (OPTs) are organic field-effect transistors (OFETs) with light responsive function. The OPTs show high sensitivity and low noise, which can be readily applied in organic electronic circuits. For the fabrication of high-performance OPT devices, organic semiconductors and interlayers play a crucial role. Various -conjugated molecules, have been used in OPT devices, including pentacene. The light sensitivity of OPT devices containing pentacene has been extensively reported in literatures [1]. On the other hand, graphene has been studied intensively for its promising properties in electronics [2]. Fluorographene (FG) has attracted great interest for potential applications due to its tunable band gap [3], however, the application of FG in OPT devices has not been reported. Therefore, it is of importance to fabricate excellent OPTs with FG as a modification layer. Although various attempts have been payed on the modification of the dielectric surface [4] to improve the performance of OTFTs, it is worth of trying with FG nano-sheets as the modification layer. We have investigated OPTs with FG nano-sheets, pentacene and the like. High-performance OPT devices have been fabricated using pentacene or bitriisopropylsilylethynyl tetraceno[2,3-b]thiophenes (TIPSEthiotet) as a semiconductor layer. FG nano-sheets are inserted into the interface between organic semiconductor layer and gate dielectric. The effects of the interface modification layer on the properties of OPTs are investigated. Photoresponsivity and photocurrent/dark-current ratio are increased dramatically due to the presence of the modification layer. For the FG-modified devices based on TIPSEthiotet, a maximum photoresponsivity of 21.83 A W^-1 and photocurrent/dark-current ratio of 1.85 x 10^6 are obtained under white light irradiation. While, for the FG-modified OPT device based on pentacene, a high photoresponsivity of 144 A W^-1 and a low optical power of 25 W cm^-2 are obtained under the same condition. This photoresponsivity value is higher than that for most OPTs based on pentacene reported under same conditions. Moreover, for the devices with FG modification layer, mobilities are also increased distinctly. These increases can be ascribed to strong electron trapping ability of the fluorine atoms in the FG nano-sheets and the well-known photovoltaic effect. The results indicate potential application of FG-containing devices in optoelectronic and photonic area.
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J. Am. Chem. Soc., 2009, 131, 9396.