| Hybrid thin films consisting of semiconductor nanorods arrayed in a polymer matrix have shown great potential as integral parts of next-generation flexible, low-cost devices for energy generation and storage. Challenges in the development of such nanocomposites are twofold: 1) Uniform alignment of nanomaterials in the film must be ensured across arbitrarily large regions and 2) Morphology and spatial density of nanorods in the film must be well-controlled to match physically relevant length scales of the specific application. Traditional lithographic and top-down methodologies of synthesis and assembly, though effective to these ends, are wholly unsuitable for low-cost roll-to-roll processing. Here, several methods for achieving the aforementioned goals based on self- and directed-assembly are developed, leveraging thermodynamic behaviors of carefully engineered systems coupled with the application of applied fields including shear and magnetic fields to achieve high levels of control of nanoscale objects across large areas. In particular, the targeted application of high efficiency bulk heterojunction photovoltaics (PV) is addressed. Using solution-synthesized ZnO nanorods as a prototypical semiconductor system, aligned ZnO-polythiophene nanocomposite thin films suitable for PV are demonstrated. Integrating controlled-density ZnO arrays as nanotextured electrodes, we observe significant normalized power conversion efficiency (PCE) enhancement over corresponding thin film devices based on morphological considerations alone. More generally, the ability to tune morphology and density of nanorod arrays provides the unique ability to rationally optimize for any targeted applications in a low-cost, scalable manner and offer opportunities for a greater understanding of transport and loss mechanisms in functional hybrid systems. |
