Tailoring of Organic Semiconducting Materials for Energy Applications

Abstract

Organic semiconductors offer several advantages, including low-cost fabrication, flexibility, and solution processability. These features have made them a focus of extensive research over the past decades. Among many approaches, donor-aceptor (D-A) structures, consisting of electron-rich moieties (donor) and electron-deficient moieties (acceptors), have become an essential design concept. The D-A configuration enables precise tuning of energy levels, strong intermolecular interactions, and enhanced charge carrier mobility, making these materials highly promising candidates for diverse organic semiconducting devices including organic solar cells (OSCs), organic thermoelectrics (OTEs), and organic field-effect transistors (OFETs). In this work, we systematically investigate molecular-level design approaches aimed at improving the performance of organic semiconductors. First, selenium substitution was investigated in conjugated polymers to optimize doping efficiency and thermoelectric properties. By strategically replacing sulfur with selenium in the backbone, improved p-doping efficiency and enhanced power factors were achieved, demonstrating the potential of heteroatom substitution in organic thermoelectrics. As a second aspect, the relationship between the conjugated polymer’s molecular weight and its electrical and thermoelectric properties was systematically explored. A comparative study of polymer samples with different molecular weights confirmed relationships among molecular weights, doping efficiency, charge carrier mobility, and crystallinity retention after doping. These findings underscore the importance of precise molecular weight control to maximize thermoelectric performances. Lastly, side-chain tuning of non-fullerene acceptors (NFAs) was employed to overcome solubility limitations and aggregation issues in large-area OSCs processed by non-halogenated solvent, o-xylene. By incorporating asymmetrically elongated branched alkyl chains, the solubility of NFAs and mophology of acitve films in non-halogenated solvents were significantly enhanced. This modification facilitated the realization of OSC modules that are both efficient and scalable, accompanied by enhanced morphological features and improved photovoltaic output. It offers a viable direction for the advancement of sustainable OSC technologies. Collectively, this research highlights the critical role of backbone modification, molecular weight optimization, and side-chain modification in tailoring key electrical characteristics and structural properties in organic semiconductor systems. These results offer practical guidance for designing efficient organic optoelectronic and thermoelectric devices, paving the way for next-generation energy solutions.