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

• Highly-sensitive diF-TESADT phototransistor were fabricated and characterized.
• Positive gate bias improved the light responsivity of diF-TESADT phototransistor.
• Qualitative calculation of trapped charges from the threshold voltage shift of transistor.
• Photoinduced write and erase were found from diF-TESADT transistor.

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 (VTH) shift under a white light illumination in which the response time was estimated to be <0.5 s and a current modulation greater than 106. It was found that the VTH shift can be further enlarged by an additional gate bias, achieving very high light responsivity >103 A/W at 0.17 mW/cm2 and IPH/IDARK ratio higher than 106. Also, by applying an erase gate bias, fast recovering of VTH 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.

Figure optionsDownload as PowerPoint slide