Application Of Admittance Spectroscopy-based On Mathematical Equations To The Organic Semiconductor Research

In this paper, the main content is application of admittance spectroscopy-based on mathematicalequations to study the charge transport properties of organic semiconductor materials. Firstly,starting from the current density equation and poisson equation, we establish a theoreticaladmittance (impedance) model, which include dispersion parameters and charge carrier transporttime of organic semiconductor, under different boundary conditions based on the space chargelimited current theory. Then appling particle swarm optimization (PSO) algorithm to fit the real partand imaginary part information of experimental impedance for getting the unknown parameters inthe model. At last, calculate the carrier mobility and other physical quantity which we need tomeasure. In addition, the equivalent circuit model also used in this paper.The main content is as follows:(1) Through a large number of literature research, we systematically introduce the basicconcept and basic principle of admittance spectroscopy, and summarize several theory admittancemodels under different conditions and some concrete applications in organic semiconductorresearch. And the basic admittance model is deduced in detail-single carrier transport admittancemodel with no trap, and then simplely discusses analysis. This chapter introduce admittancespectroscopy theory overall and how to use admittance spectroscopy to study organicsemiconductor features detailedly.(2) Preparation of organic semiconductor device ITO/NPB (1200nm)/Ag, and measure the realpart and imaginary part information of impedance. Based on the basic admittance model, usingparticle swarm optimization (PSO) algorithm to obtain the dispersion parameters and hole mobilityof NPB. The hole mobility of NPB calculated from this method meet Poole-Frenkel formula, andthe results are in consistent with other reported literatures. Finally, we make a detailed comparisonbetween the particle swarm optimization algorithm and the general least squares algorithm, PSOshows its unique advantages in processing data for complex model formula.(3) Based on the theory of admittance spectroscopy, we analyse the effect of metal oxide V2O5MoO3, WO3to hole mobility of NPB. Preparation of three groups devices with metal oxide bufferlayer and a set of reference device, and measure the hole mobility. The results show that the metaloxide as the hole injection buffer layer can change the anode interfacial potential barrier and theimpedance of the device, and affect the hole injection ability and transport characteristic, and affect the carrier mobility.(4) Using self-assembly method to preparate single and double chain DNA molecule probes,and on the basis of admittance and impedance spectroscopy principle, applying admittance modeland equivalent circuit model, tentatively measure the mobility of DNA biological molecules andexplore its macroscopic charge transport mechanism. Ting-Yu Lin measured DNA molecularmobility by use time of flight (TOF) and the difference of them is very big, we give some specificreasons.