From crystalline growth to charge transport: simulations of organic semiconductor thin films for sustainable electronics

Organic semiconductors (OSs) are crucial for the development of organic electronic devices, increasingly recognized for their potential to address global challenges related to energy sustainability and the transition to carbon-free technologies. These devices offer advantages over traditional inorganic counterparts, including mechanical flexibility, lightweight design, and cost-effectiveness. However, their efficiency remains lower than that of inorganic materials, making them an attractive subject for further study and improvement. The performance of OSs is closely tied to molecular packing and charge transport properties within thin films, yet these remain difficult to characterize due to the complexity of the underlying interactions. Simulations offer an advantage over experimental methods by enabling precise control of system parameters, which is essential when investigating atomic-scale processes that govern molecular organization and charge transport in organic semiconductor thin films. This thesis leverages advanced simulation techniques, combining molecular dynamics (MD) simulations for vapor-phase deposition with quantum mechanical (QM) methods for charge transport, to gain insights into the interplay between molecular packing, crystallinity, and electronic properties. The work presented in this thesis consists of two primary simulation approaches. First, MD simulations of vapor-phase deposition were conducted to examine growth mechanisms and molecular arrangements of organic thin films under various conditions. This study, focusing on materials such as pentacene, perfluoropentacene, diindenoperylene, and dicyanovinyl derivatives, revealed how intermolecular interactions and deposition conditions influence film morphology, crystallinity, and defects. Second, a novel Surface Crystal Structure Prediction method was developed to model surface-induced polymorphs and crystalline structures, incorporating substrate effects to predict realistic surface-level molecular arrangements and unit cells. Additionally, charge transport simulations were performed to analyze how morphology, defects, and surface interactions affect charge mobility. The findings highlight the importance of crystalline regions for efficient charge transport and provide insights into how molecular design and deposition conditions can enhance device performance.