BRIGE: Photovoltaic Mapping of Gradients to Determine Structure-Function Relationships in Organic and Nanocrystalline Solar Cells

University Of California-San Diego, La Jolla CA

Investigators

Abstract

Technical description: Organic and nano-crystalline solar cells require an order of magnitude less active material than other ?thin-film? photovoltaic devices. This BRIGE project will introduce a new experimental framework in which to study organic solar cells, with three goals: (1) to improve the quality and reproducibility of data obtained from organic and nanocrystalline solar cells, (2) to reduce drastically the time and resources needed to characterize them, and ultimately (3) to increase their photovoltaic efficiencies. At the core of the proposed framework are the generation of compositional or morphological gradients within semiconductor thin films and the measurement of spatially resolved photovoltaic "maps" of these gradients using a new type of non-damaging liquid metal probe. We refer to the proposed technique as photovoltaic mapping (PVMAP) of gradients. PVMAP, once developed, can be used to pose hypotheses about ultrathin photovoltaic films that cannot be tested using serial techniques. PVMAP will be used to determine the extent to which thermal annealing below the melting temperature of a semiconducting polymer-fullerene composite film increases the fraction of crystallites oriented with their ð-stacking axes perpendicular to the electrodes. PVMAP can also be used for the systematic optimization of organic solar cells by iterative mapping of different gradients (analogous to "directed evolution"). Broader significance and importance: Global capacity for photovoltaic electricity has increased at a rate of sixty percent per year for the last five years. Continuation of this trend requires new devices that operate with high efficiencies at low cost. One candidate is solar panels based on plastic materials. One of the reasons that these devices are not yet competitive with those based on silicon is that the details of their operation cannot be understood efficiently using current experimental techniques. This project will allow researchers to gather information about organic solar cells much more quickly than is currently possible. The proposed technique works by combining many materials and characteristics in a single device, in which different areas containing different combinations of properties can be measured separately. The technical portion of this proposal, along with its efforts to integrate research, education, and opportunity for underrepresented students, will help remediate the environment and create jobs in an economy that includes renewable energy. Broadening Participation activities: The PI is the Diversity Officer in the Department of NanoEngineering at UCSD. This proposal would support: (1) paid summer internships for IDEA (Diversity) Center Scholars; (2) an outreach event for middle school students from predominantly Hispanic neighborhoods in San Diego; and (3) a program for high school girls hosted by the UCSD Society for Women Engineers. A fourth effort focuses on the outcomes of these activities on the educational and career choices of participants. The PI will work with the IDEA Center at UCSD to develop surveys, sent periodically to participants. Results and a quantitative analysis will be submitted to a peer-reviewed journal, such as the Journal of Engineering Education. A quantitative understanding of the factors that lead underrepresented students toward careers in science and engineering (and the factors that cause them to withdraw or change fields) will be critical to the PI's efforts to expand opportunity and will play a major role in being able to secure funding from NSF for additional scientific projects and for innovative programs to broaden participation. This research has been funded through the Broadening Participation Research Initiation Grants in Engineering solicitation, which is part of the Broadening Participation in Engineering Program of the Engineering Education and Centers Division.