Carrier accumulation in organic heterojunctions controlled by polarization

Abstract

The diode operation of OLEDs is characterized by the creation of a conductive space charge region in an insulating neutral dielectric region under the voltage application. It contrasts with the semiconductor diodes, where an insulating space charge region is created in a conductive charge neutral region. We proposed a heterojunction theory based on the quasi-conductor concept to give a unified view, which gave a modified Mott-Schottky equation for OLEDs (Org. Electron. 61, 10 (2018)). Based on this theory, we proposed a new mobility evaluation method using modulus spectroscopy and reported an in-situ simultaneous evaluation of mobilities and carrier densities of carrier transporting materials in a practical OLED configuration (Jpn.J.Appl.Phys. 59(7), 071005 (2020)). However, there were invalid handlings of the boundary conditions. We carefully reconsider the connection of the electric fields through the insulating and conductive regions based on the Dynamic Modulus Plot (DMP) analysis. It is proposed that the density of the accumulated carriers is governed by the fixed interface charges rather than the Activation of Localized Carrier Source (ALCS). Despite the errors in the previous derivation, the revised theory also gave luckily the same expression of mobility as a result, to ensure the validity of the quantitative estimation in the previous report.