Oğuz Köysal

Investigation of photo-induced change of electro-optical performance in a liquid crystal-organic field effect transistor (LC-OFET)

Abstract This study aimed to improve the electrical characteristics of poly(3-hexylthiophene) (P3HT) and liquid crystal-organic field effect transistors (LC-OFETs) under UV illumination. Consequently, a novel LC-OFET was fabricated using a nematic liquid crystal (E63) and a P3HT mixture in an OFET cell. Cell thickness was determined through field emission scanning electron microscopy. For assessment of the electrical characteristics, the LC-OFET device was exposed to various UV light intensities in total darkness for the purpose of obtaining the output- and transfer-current voltage. The capacitance–frequency plot of the capacitor cell was then measured to determine the main parameters including the threshold voltage (VTh), field effect mobility (μFET) and current on/off ratio (Ion/off) of the device. Thus, the full characterisation and UV light response of the electronic parameters were determined for this new class of transistors. Results showed that the new LC-OFET exhibited good performance in the form of low VTh, high μFET, and high Ion/off.

The impact of NiPc additive and laser light dielectric properties of E63 nematic liquid crystal

ABSTRACT In this work, the electrical properties of the pure nematic liquid crystal (E63) and different concentrations Nickel Phthalocyanine (NiPc) doped (E63+1%NiPc, E63+3%NiPc and E63+5%NiPc) E63 have been investigated by means of dielectric spectroscopy measurements under laser light illumination. The variations of the real () and imaginary () parts of dielectric constant with frequency have been studied. According to versus voltage graphics, threshold voltage, Vth has been calculated. It has been observed that while NiPc doping increases the Vth, the application of laser light has a remarkable decreasing effect on threshold voltage, Vth. The absorption coefficients, , and relaxation times, , have also been calculated for determining the relaxation mechanism. It has been revealed that the relaxation type of these materials is nearly-Debye type regardless of the laser illumination. Moreover, the dielectric strength has been analysed both Debye and Cole-Cole models. Furthermore, conductivity mechanisms of these composites under dark and laser illumination have been investigated for four frequency regions. It has been shown that conductivity mechanism of the composites are not affected by application of laser light above .