The hole drift current induced electric field at hole injecting electrode/organic interface and its influence on Gaussian disordered states

Abstract

Two different sets of published temperature dependent current-voltage N,N´-Di(1-naphthyl)-N,N´-diphenyl-(1,1´-biphenyl)-4,4´-diamine organic semiconductor data are analyzed. The general solution of Poisson equation with the imbedded charge traps reduced to the low trap concentration limit provides the simple current density – voltage relationship on which analyses are based. The relationship is expressed in terms of two parameters: the electric field at the hole injecting interface, Eint, and the hole mobility, μmax, determined by the measured current density at the maximum value of the externally applied electric field, Ea, in a given experiment. It is shown that Eint explicitly depends upon the current density, j, on the negative interfacial charge (areal) density proportional to Eint - Ea, and on the concentration of the embedded holes. For cases where Eint is constant the current density within the organic diode structure is space charge limited (SCLC). Then the calculated weak Ea dependent hole drift mobility, μd, attains the shape of well-known exponential bias dependent mobility. From the current-voltage data not complying with SCLC characteristic the Ea dependence of Eint is calculated and its detrimental effect on the hole drift mobility is presented. An estimate of Ea dependent thickness of the interface slab is made. The effect of the deduced Ea dependent interfacial electric field, Eint, on Gaussian disordered states is examined.