Several types of thin film solar cells have recently drawn a great amount of attention, due to its huge potential in solar energy harvesting. However, the energy conversion efficiency of the well-known solar cells is still far from the theoretical expectation. The low efficiency is due to inefficient light absorption by the semiconductor and limited carrier extraction from the semiconductor to the external load. These two factors are closely related, which makes the development of a solution more difficult. Development of the thin film solar cells using the surface plasmons of the nanostructures will address this difficult problem and contribute to furthering the goal of energy security of the US. Given that the electricity produced from solar radiation is only about 1% of the total annual electricity consumed in the US, the success of this research will contribute to increasing US's energy security by providing highly efficient thin film solar cells. The integration of the anticipated research accomplishments with existing and new classroom courses will also improve the quality of engineering education on nanoscience and renewable energy at the University of Pittsburgh. In addition, the multi-disciplinary nature of the project will provide undergraduate and graduate students with the opportunity to be exposed to new frontiers in design, fabrication and characterizations of materials and devices, beyond the boundaries of their disciplines. Finally, this project will be aimed at using research products such as thin film solar cells to reach underrepresented groups, which will be coordinated with on-going efforts of the University of Pittsburgh to expand the participation of underrepresented groups in engineering education.
Current problems associated with the thin film solar cells clearly show a strong need for design of a new nanostructure that can enhance the light absorption and carrier transport in the thin film semiconductor. One very promising way is to exploit resonance phenomenon, such as surface plasmons. However, popular plasmonic metal nanoparticles have several drawbacks to be implemented to the thin film solar cells. In this project, a propagating surface plasmon on 1-dimensional photonic crystal/metal thin film interface will be used to circumvent the problems of the metal nanoparticles. The new nanostructure will increase the light harvesting efficiency without increasing the thickness of the semiconductor film (i.e. decreasing the carrier collection efficiency). The objective of this project is to fabricate a new junction-type thin film solar cell employing the photonic crystal based plasmonic nanostructure and to explore the physical interactions among propagating surface plasmons, solar light modulation, and carrier/exciton generation. Progress of the research will create the fundamental understanding of the photon-exciton conversion under the influence of the surface plasmons for the thin film solar cells. For this purpose, the nanostructured photonic crystal will be designed to excite the surface plasmons that interact with incoming solar light in a visible range. In addition, basic understanding of light-matter interactions and radiative properties of nanostructures will be pursued. The intellectual significance of this project is that new directions for highly efficient hybrid solar cells will be provided. Knowledge on surface-plasmon-assisted tuning of the light absorption will facilitate a new class of photovoltaics which is not limited by the tradeoff between light absorption and carrier transport.
