Highly-sensitive solution-processed 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TESADT) phototransistors for optical sensing applications

초록

A highly-sensitive organic phototransistor, based on solution-processed 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TESADT) was fabricated and investigated for an optical sensing element. The phototransistor based on thin crystalline grains of diF-TESADT exhibited a significant threshold voltage (V-TH) shift under a white light illumination in which the response time was estimated to be <0.5 s and a current modulation greater than 10(6). It was found that the V-TH shift can be further enlarged by an additional gate bias, achieving very high light responsivity >10(3) A/W at 0.17 mW/cm(2) and I-PH/I-DARK ratio higher than 10(6). Also, by applying an erase gate bias, fast recovering of V-TH to the initial position was possible. This phenomenon can be ascribed to the trapping and de-trapping of photo-generated carriers at the organic channel/dielectric interface, while the amount of trapped carriers can be also modulated simultaneously by the gate bias. This investigation identifies that the solution-processed diF-TESADT phototransistors can be used for large-area and low-cost optical sensors and memory applications. In particular, it can be claimed that performance improvement by a gate bias represents a universal method applicable to the organic phototransistors. (C) 2014 Elsevier B.V. All rights reserved.

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