Online

Rice, Robin Alexander

Graduate Program in Materials Science

2021

M.S.

Impedance Spectroscopy (IS) is an increasingly common technique to characterize both solid state and electrochemical systems including solar cells and light emitting diodes (LEDs). However, IS relies on a system response being linear with its input such that a time invariant impedance can be defined. This is usually achieved by a small amplitude input. However, doing so suppresses responses of the nonlinear processes which are of considerable interest to those designing and optimizing these devices, such as charge carrier recombination and space charge effects. This investigation employs the recently developed nonlinear extension to IS (NLIS) based in Fourier analysis of the measured harmonic current such that a nonlinear definition of higher harmonic admittance (inverse impedance) is established. By relating Fourier coefficients of the measured current with derivatives of the voltage specific transfer function we may extract valuable physical parameters of the system in question. Benchmark tests of this technique on systems of known transfer functions will be presented specifically measuring hole mobility from space charge and the diode ideality factor from recombination limited current regimes. Finally, NLIS is used to characterise 2-(7-{4-N,N-Bis(4-methylphenyl)aminophenyl}-2,1,3-benzothiadiazol-4-yl)methylenepropanedinitrile (DTDCPB), a promising novel intramolecular charge transfer (CT) organic semiconductor (OSC). The first known report of DTDCPB hole mobility is presented.