UC Berkeley

Organic semiconductors hold the promise of electronic devices whose manufacturing scalability and form factor versatility could disrupt the existing electronics market. From a commercial feasibility standpoint, however, the technology is still in its relative infancy. To date, significant research effort has been directed toward developing polymers and small molecules for use in solution-processed thin-film bulk heterojunction organic photovoltaics (BHJ OPVs) and field-effect transistors (OFETs). A key goal of this research is to better understand the structure-property relationships that govern material performance. Molecular structure has been shown to influence material properties such as light absorption, intermolecular electronic compatibility, charge transport characteristics, thin-film morphology, and molecular packing. Similarly, processing steps such as the use of certain electronic interlayers or the incorporation of solvent additives can have a dramatic improvement on device performance.

In this work, polymer and small molecule systems are used to investigate such structure-property relationships, particularly ones governing solid-state nanostructure. Seemingly small changes in structure are shown to have a significant and systematic impact on OPV and OFET device performance. We investigate how a solution-processed organic semiconductor's π-conjugated backbone, end-capping groups, and solubilizing aliphatic side-chains can have a profound impact on nanostructure and device performance. In addition, we study how the processing conditions of polymers used in OPV and OFET devices affect solution-phase thermodynamics, as well as the dynamics of spin-coating and film formation. In both polymer and small molecule systems, we have demonstrated forward-looking design and processing principles that can inform the development of the next generation of ever higher-performing OPV and OFET materials.