Impact of crystallinity and grain density on the charge-carrier distribution and transport in organic semiconductors

The crystalline and amorphous phases often coexist in the organic active layers of their electronic devices, which further undergo morphological changes over time. Understanding of the characteristics of the microscopic processes in polycrystalline organic films is essential for optimizing organic semiconductors and their devices, particularly in the context of flexible electronics. Here, we systematically investigate the charge-carrier distributions and transport in polycrystalline organic films, focusing on the impact of the crystallinity and grain density. These polycrystalline morphology data were generated from an efficient Monte Carlo method, which were then incorporated into molecular-level device simulations that can describe the microscopic chargetransport processes. These results demonstrate the distributions and transport characteristics of charge carriers in different phases of the polycrystalline organic semiconductor films, as well as the influencing factors. Importantly, we show that the influence of a polycrystalline morphology becomes more pronounced at low driving voltages, which has been the subject of significant research efforts. Our study also revealed a decrease in mobility at low crystallinities, a phenomenon that was not previously anticipated.