Study Of Interface Trap Free Energy,Prefactor And Trap State Density Of Organic Semiconductor Through Admittance Spectroscopy

According to the space-charge-limited current theory, the theory model of admittance spectroscopy which describes the charge transport mechanism can be established under boundary condition. In this paper, the organic semiconductors charge transport properties with the application of admittance spectroscopy has been studied. Admittance spectroscopy runs through the whole paper, and we make research of the organic semiconductors in the aspect of the thickness dependence hole mobility, field dependence factor, distribution of trap and so on. The theory model of admittance spectroscopy, trap distribution, field dependence factor are described detailedly and applied.The main content is as follows:(1) We systematically introduce the original concept and basic principle of admittance spectroscopy through a large number of literature research, introduced the mechanism of the carrier transport, mobility model and summarize the single-carrier admittance theory model without trap, single-carrier admittance theory model with exponential distribution, admittance theory model when considering the relationship between mobility and carrier concentration, admittance theory model when considering interface trap states and the application of organic semiconductor in mobility, trap states, negative capacitance.(2) Prepare two kinds of organic semiconductor devices ITO/NPB(50nm-800nm)/Al,ITO/TPD(50nm-800nm)/Al and measure impedance information, we get the relationship between carrier mobility and the thickness by the application of particle swarm optimization(pso) algorithm. The outcome indicates that the mobility increases as the thickness increases and it approaches the stable value at 600 nm. The crystallization and morphology influence factors are excluded through XRD and AFM. At last, we propose the conception of interface trap free energy from thermodynamics to explain this phenomenon(3) There are many factors which influence the mobility, such as carrier concentration, electric field, temperature, pressure, molecular orientation and purity, etc. Field dependence factor and zero-filed mobility are the major parameters of the Poole-Frenkel( P-F). We summarize the research status of the field dependence factor, then discuss the two physical parameters to explore their connection with the thickness dependent mobility of organic semiconductors.(4) Deduce the model of trap state and study the new synthetic efficient blue materials PhTPFOR and DPhDPFOR with the applications of admittance spectroscopy. We obtain the trap state density of these two materials by capacitance-voltage curve, Mott-Schottky equation, and summarize the feasibility of admittance spectroscopy method for the structure similar material. This method provides a more simple and effective method to study the affecting factor of a device, for example, efficiency and lifetime.