#### Presentation Title

Nonlinear Impedance Spectroscopy to characterize Hole Transport and Recombination Dynamics in Organic Semiconductor Devices

#### Abstract

Impedance Spectroscopy (IS) is an increasingly common technique to characterize both solid state and electrochemical systems including solar cells and 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 filters 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. We present a nonlinear extension to IS based in Fourier analysis of the measured harmonic current such that a new nonlinear definition of higher harmonic admittance (inverse impedance) is developed. By relating Fourier coefficients of the measured current with derivatives of the voltage specific transfer function we may extract valuable physical constants of the system in question. Benchmark tests of this technique on systems of known transfer functions will be presented. Further, this technique may experimentally reconstruct unknown transfer functions, elucidating dynamics of electron-hole recombination and space charge current limiting device processes. I will propose such an investigation of a pair of novel intramolecular charge transfer organic semiconductors which may exhibit high dielectric constants and possible free carrier generation on photoexcitation.

#### Primary Faculty Mentor Name

Matthew White

#### Faculty/Staff Collaborators

Matthew White (Graduate Faculty Advisor)

#### Status

Graduate

#### Student College

College of Engineering and Mathematical Sciences

#### Program/Major

Materials Science

#### Primary Research Category

Engineering & Physical Sciences

Nonlinear Impedance Spectroscopy to characterize Hole Transport and Recombination Dynamics in Organic Semiconductor Devices

Impedance Spectroscopy (IS) is an increasingly common technique to characterize both solid state and electrochemical systems including solar cells and 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 filters 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. We present a nonlinear extension to IS based in Fourier analysis of the measured harmonic current such that a new nonlinear definition of higher harmonic admittance (inverse impedance) is developed. By relating Fourier coefficients of the measured current with derivatives of the voltage specific transfer function we may extract valuable physical constants of the system in question. Benchmark tests of this technique on systems of known transfer functions will be presented. Further, this technique may experimentally reconstruct unknown transfer functions, elucidating dynamics of electron-hole recombination and space charge current limiting device processes. I will propose such an investigation of a pair of novel intramolecular charge transfer organic semiconductors which may exhibit high dielectric constants and possible free carrier generation on photoexcitation.