Phototransistors Based on A Lightly Doped P3HT
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.306
Phototransistors Based on A Lightly Doped P3HT Thomas H. Debesay1,2, Sam-Shajing Sun1,2,3 1
Center for Materials Research, Norfolk State University, Norfolk, VA 23504, USA
2
PhD Program in Materials Science and Engineering, Norfolk State University, Norfolk, VA 23504, USA
3
Department of Chemistry, Norfolk State University, Norfolk, VA 23504, USA
ABSTRACT
Organic/Polymeric Semiconductor (OSC) based devices have been under extensive study for the past three decades due to their intrinsic potential advantages such as lightweight, mechanical flexibility, biocompatibility, low toxicity, abundant material availability, low cost of processing, etc. A phototransistor incorporates the properties and functions of a transistor and photodetector. In this study, a phototransistor based on a donor/acceptor (D/A) pair (photo-doping) was studied and demonstrated. Unlike in organic photovoltaics (OPV) where 1:1 proportion by mass of the donor:acceptor is utilized to make up the active layer, that ratio appears to be too high for phototransistor applications. According to literature, this 1:1 concentration leads to low overall device performance, lack of I-V curve saturation (kink effect), and bipolar behavior. By altering fabrication techniques and doping concentrations, we were able to demonstrate a donor/acceptor based phototransistor with p-type characteristics with improved performance. In this work, we fabricated a high-performance OFET based on a very small amount of Phenyl-C71butyric acid methyl ester (PCBM) doped into a Poly(3-hexylthiophene) (P3HT) host. With this work, a greater understanding behind the optimization of D/A based phototransistors is advanced.
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INTRODUCTION Among the many applications of organic field-effect transistors (OFETs), phototransistors are FET devices which contains a light sensitive semiconducting active area, that enables them to detect light of broad range of wavelengths and/or intensities. As their name indicates, their basic functionality is associated with the light under which they are illuminated, and the voltage imposed on the gate terminal of the transistor. Based on literature reports, the gate voltage modulates the conductive channel of the phototransistors [1-3]. This makes them more sensitive to light of even lower intensity than the classic two-terminal photodiodes. Most of the organic semiconductor-based phototransistors reported so far typically employ an active organic semiconducting layer that constitutes an electron donor:acceptor blend on a 1:1 proportion [4,5]. This protocol is possibly adopted from the doping mechanism used in other applications such as organic photovoltaics [6,7], where, generation and transport of the equal number of mobile electrons and h
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