With surging interest in the development of cheaper and more efficient photovoltaic Materials semiconductor nanocrystals have emerged as a promising candidate potentially offering major benefits as light harvesting elements. These materials have a number of desirable characteristics. The electronic and optical properties of nanocrystals are size-tunable, which will allow optimal coverage of the solar spectrum by structures with large cross-sections. Their compatibility with solution environments and low-temperature processing are attractive for practical and cost-effective production. Beyond their potential to transform low-cost solar energy conversion technology, nanocrystal-based solar cells also have the potential for substantially increased efficiency, based on the recently-discovered process of efficient multi-exciton generation. In this process a single incident photon can generate multiple electron-hole pairs and thereby utilize the absorbed photon energy in excess of the band gap, which would otherwise be lost as heat.
Progress in the development of nanocrystal-based solar cells is currently limited by the lack of molecular-level control over the electronic properties at the interface. Initial efforts in this field have focused on hybrid organic-inorganic devices based on blends of nanocrystals and conjugated polymers. This approach suffered from poor extraction of photogenerated carriers and illustrated that improved understanding and control over the interface properties are required to fully harness the unique photon harvesting properties of these materials. The project led by Engstrom and Hanrath leverages their expertise in surface science, nanocrystal synthesis and device fabrication to study fundamental principles of interface charge transfer and to integrate tailored nanocrystal interfaces into novel all-inorganic distributed heterojunction solar cells. The goals of their work are: (1) to understand and control the electronic structure and transport properties at nanocrystal interfaces and (2) to apply that knowledge to engineer optimized interfaces for the use of semiconductor nanocrystals in distributed heterojunction solar cells.
Beyond the scientific activities, the project will engage a number of faculty and students involved in solar energy research in a workshop on research ethics. Solar energy, being on the frontier of research, is susceptible to practices that might lead to a number of undesirable outcomes. Educating the community about the proper conduct of research, ranging from the writing of and review of proposals to day-to-day activities in the lab will better foster a productive research environment. Finally, the project is closely integrated with a number of outreach and educational activities. We have aligned with the Cornell Institute for Physics Teachers to reach out to high school teachers and students and engage them in the exciting advances being made in the field.