Optoelectronic properties of novel alkyl-substituted Triphenylamine derivatives

Abstract

Hole transport characteristics in three new organic compounds based on triphenylamine (TPA) moiety are presented. The effect on electrical and optical properties of TPA, attached with methyl or tert-butyl side groups, has been investigated through measurement of current density versus voltage (J-V), capacitance versus voltage (C-V), frequency dependent capacitance, ac conductivity, Impedance spectroscopy, UV-Vis spectroscopy, Photoluminescence (PL) spectroscopy and X-Ray Diffraction (XRD) studies. These measurements reveal that, the attachment of methyl or tert-butyl group in the para-position of the TPA moiety leads to improved optoelectronic properties and greater molecular stability. XRD analysis of the samples indicates that the inter-molecular distance is the lowest for TPA with tert-butyl side group (3.43 Å) as compared to pure TPA (3.57 Å). This leads to stronger inter-molecular interaction as evidenced by the UV-Vis spectra. PL studies indicate significant Quantum Efficiency (?30%) for alkyl attached TPA. In order to get a better understanding of the charge transport phenomena, the effect of molecular structure dynamics on charge transfer kinetics is analyzed by evaluating the charge carrier hopping rate coefficient and dynamic state factor. The dynamic state factor b has higher value for lower bias voltage, corresponding to dc conductivity, whereas, at higher bias, the value of b is smaller, indicating the dominance of ac conductivity. Hopping conductivity is seen to be highest for the device with tert-butyl substitution in TPA moiety. Our experiments indicate an order of magnitude enhancement in charge carrier mobility for alkyl-substituted TPA. © 2017 Elsevier B.V.