We study using three-dimensional kinetic Monte Carlo (KMC) simulations to what extent the formation of Schottky contacts between a metal electrode and a molecularly doped disordered organic semiconductor can be understood from the theory for crystalline inorganic semiconductors, adapted to include the effects of the localized nature of the states in which the charge carriers reside and the hopping transport in between these states. The thickness of the Schottky-contact depletion region is found to be significantly smaller than as expected when the energetical disorder is neglected. The presence of energetic disorder is also found to influence the voltage dependence of the width of the depletion regions near the contacts of single-layer double-Schottky-contact devices. The voltage drop over the two depletion regions and the remaining charge-neutral bulk layer is shown to be described successfully by a semianalytical model, based on an accurately parameterized bulk mobility function of the dopant concentration, energetic disorder, and the electric field. We furthermore find that the mobility in the depletion regions is drastically reduced. As a result, the depletion-region formation process can be ultraslow, with a characteristic time scale ranging from microseconds to beyond milliseconds.
Bibliographical noteFunding Information:
This work is supported by the talents project of Guangdong Province, the National Key R&D Program of China (No. 2021YFB3600601), National Natural Science Foundation of China (No. 62005083), Science and Technology Program of Guangzhou (No. 2019050001), the leading talents of Guangdong Province Program (No. 00201504), Program for Chang Jiang Scholars and Innovative Research Teams in Universities (No. IRT_17R40), Guangdong Provincial Key Laboratory of Optical Information Materials and Technology (No. 2017B030301007), the Grant of 2019 Guangdong Recruitment Program of Foreign Experts (No. 191900017), National Center for International Research on Green Optoelectronics, MOE International Laboratory for Optical Information Technologies and the 111 Project.