The objective of this research program is to identify the critical morphological parameters that control optoelectronic function in polymer/fullerene solar cells. The active layer in polymer-based solar cells is usually prepared by arresting the phase separation of a polymer/fullerene blend. The structures formed with this non-equilibrium process are difficult to control and accurately characterize, so it is hard to understand how film morphology influences the device efficiency. This award will develop three integrated tasks to investigate the effects of domain size, interfacial area and polymer crystallinity on charge generation, recombination, and transport processes, respectively. First, conductive polymer nanostructures are prepared by electron-beam patterning. These nanostructures are solvent-resistant and thermally-stable, and variables such as nanostructure geometry, polymer crystallinity, and polymer cross-link density are all tunable. Second, the optoelectronic performance of model nanostructure/fullerene solar cells is evaluated with established spectroscopic and device characterization techniques. Last, domain size, interfacial area, and crystallinity are accurately quantified with detailed analysis of X-ray scattering data. A particular focus of this work is interfacial engineering: It is hypothesized that polymer/fullerene interfacial composition profiles can be controlled through polymer cross-link density (in addition to annealing temperature and time), offering a simple route to study the effects of interfaces on charge generation and losses. The knowledge acquired through these systematic studies will identify the optimal design attributes for a benchmark polymer/fullerene system and guide morphology optimization for a variety of high-performance materials.
NON-TECHNICAL SUMMARY:
Polymer-based solar cells show promise for low-cost solar energy conversion, but the technology will not be viable as an alternative source of energy until the power output is improved. This research program facilitates those improvements by establishing a system to study the relationships between active layer structure and electronic function. These findings will help optimize the efficiency of polymer-based solar cells. Education and outreach activities are integrated with this research program in four ways. First, the PI encourages research participation for a diverse pool of high school, undergraduate and graduate students, and participates in numerous K-12 outreach programs that introduce polymer science to under-represented groups in science and engineering. Second, students will be equipped with the necessary skills for multidisciplinary research through a new nanofabrication course and a multi-institutional workshop that will teach the fundamentals of X-ray scattering. Third, through connections to the local Houston materials industry, students will learn about commercialization of polymers for energy conversion and storage. Finally, to enhance the global awareness of student participants, the PI will coordinate complementary research collaborations with the Korea Advanced Institute of Science and Technology.
