Correlation between charge-carrier distribution and local crystallinity in organic films

Abstract

Understanding charge transport in organic semiconductor films is essential for optimizing organic electronic devices. Organic films often exhibit complex morphologies, consisting of crystalline and amorphous phases, which significantly affect charge carrier distribution and transport. Moreover, film morphologies evolve under operational conditions, especially in flexible devices that are subjected to mechanical stress. Here, we investigated the relationship between charge-carrier distribution and film morphology in organic films based on device-level simulations. A Monte Carlo method for morphology generation and master equation simulations were employed to obtain steady-state charge-carrier densities. Our results showed a strong correlation between local charge density and local crystallinity near the injecting electrode in hole-only devices. However, this correlation diminishes between the electrodes and near the collecting electrode. Additionally, the strength of the correlation is dependent on the grain size, the observation length, the energy-level difference between phases, and the applied voltage; these phenomena revealed the detailed features of nonuniform charge-transport pathways in organic films. These findings provide insights into the relationship between film morphology and charge transport, informing the optimization of organic electronic devices, particularly flexible ones that operate under mechanical stress.