Increasing solar cell efficiency and affordability are critical objectives for achieving energy sustainability. The use of semiconducting nanomaterials paired with organic semiconducting polymers offers promise here, with the possibility to realize cost effective high performance heterojunction devices. Current approaches however are limited by small exciton diffusion lengths and the sub-optimal transport characteristics of the percolated nanomaterial aggregates found in today?s state of the art devices. Overcoming these limitations can lead to significant breakthroughs in solar cell performance. This proposal aims to address the above mentioned limitations. The proposed work is a 3-year project that focuses on the synthesis of novel nanomaterials with long excitonic lifetimes such as GaN single walled nanotubes, and the use of well aligned self-assembled mesophases as templates for the directed assembly of these novel nanomaterials. Assembly of anisotropic nanomaterials in nm-spaced arrays will provide significantly increased photo-induced charge transfer by providing electron-hole dissociation surfaces of high, controllable periodicity, separated by length scales that are smaller than the exciton diffusion length itself. . Dissociation at these aligned surfaces provides direct electron conduction pathways to the external electrodes of the device. The organization of this high surface area for exciton dissociation will be accomplished using methods that are scalable and do not require advanced lithography. Harmonic analysis will be leveraged to considerably enhance both ab initio calculations of the electro-optical properties of novel nanomaterials and design of experiments in the multi-parameter space that correlates photo-voltaic performance with material composition and device assembly.
NON TECHNICAL SUMMARY: The proposed work will provide the design basis for clean and sustainable energy generation. Successfully executed, it will result in new materials and processes enabling higher efficiency and more cost-effective solar cells. This project has a broad technical impact as the materials and methods developed during the course of the basic research can be applied in other areas such as thermoelectric energy harvesting, light emitting diodes, photodetectors and advanced chemical separations. A number of educational and outreach activities have been integrated into the proposed work. These include a research seminar program run in partnership with three undergraduate focused institutions, recruitment of students, especially from underrepresented groups, for summer research projects and the creation of a new module on experimental design for the introductory undergraduate Chemical Engineering course at Yale University. The impacts of the proposed research overall are: (1) Development of new science that will drive transformative advances in solar technology (2) Development of materials and methods with a broad range of technological relevance beyond photovoltaics (3) Highly interdisciplinary training of graduate students and researchers cutting across chemistry, materials science and mathematics (4) Involvement and mentoring of undergraduate students in research (5) Recruitment of underrepresented groups to science.
This project used a host of experimental and theory tools to develop understanding of solar cell materials concentrating on assembly of the various materials in the composite affects overall properties. We focused on organic (polymer)-inorganic composite solar cells and examined the interfaces between materials in order to optimize the solar cell performance. An important consideration when designing materials for solar applications is assembling them in a manner where components are well contacted and efficient pathways for the charges to reach the electrodes exist. Accomplishments of this project include; methods of alignment of carbon nanotubes and zinc oxide nanowires in a polymer phase, optimization of transparent electrodes, direct covalent bonding of quantum dots to carbon nanotubes and design of composite polymer solar cells with high efficiency. Theory was also developed to understand the interaction between the different components of our composite materials. Student outreach was also a major activity of our project; we have created projects for undergraduates to participate in meaningful research at Yale including students from non-PhD granting Universities. The students attend group meetings and learn about research beyond their projects. The PI and co-PIs have given public lectures on our solar energy projects, have helped judge local high school science fairs and participated in the training of public High School students. For example including a Science Saturdays lecture posted on You Tube, and a professional development workshop for New Haven Public School system teachers where he gave a lecture on directed assembly and solar energy. Our research team was composed of researchers mostly from under-represented groups in STEM so we appreciate how important good exposure to science is.
