This project is co-funded by the Divisions of Materials Research, Chemistry, and Mathematical Sciences.
A team of chemists, materials scientists, and engineers at Pennsylvania State University is joined by a mathematician at the University of Delaware to investigate light-harvesting thin films for solar cells that contain plasmonic nanostructures coupled to periodic dielectrics. The project links the concepts of strong light scattering by sub-wavelength metallic structures with the light-trapping and light-guiding properties of photonic crystals. These structures are called multiplasmonic because they support the propagation of multiple surface plasmon-polariton (SPP) modes and can utilize both s- and p-polarized incident light. They offer promise for substantially increasing the utilization of light in thin film photovoltaic cells. This concept is explored computationally and experimentally in thin film semiconductor and planar dielectric light-concentrating architectures. The Rigorous Coupled Wave Approach is used to simulate and optimize light scattering and propagation. Because these calculations are time-intensive, mathematical research is planned to develop more efficient algorithms that will incorporate the optical properties needed to provide physically meaningful solutions. A fully 3-D time domain simulation tool will then be developed to enable broadband modeling of the multiplasmonic structures. In concert with the computational effort, the multiplasmonic concept is tested and validated in several experimental architectures. The simplest of these is a conventional SPP scattering layer, consisting of a metal backing film with a grid of scattering centers on a thin film multi-junction cell containing layers of polycrystalline or amorphous semiconductors. This structure allows the computational model to be validated in a photovoltaic cell and is expected to quantify polarization and multi-mode effects. Planar concentrator architectures containing periodic oxide or polymer dielectric layers with heterogeneously integrated silicon microcells are studied as photovoltaic modules. These designs are extended to a spectrum-splitting module that combines dye-sensitized solar cells and multiplasmonic silicon cells. New optical nanostructures and new patterning techniques are developed in order to fabricate these modules.
The large-scale implementation of solar photovoltaic power, a renewable resource that has the potential to dramatically impact the global energy economy, is limited by cost. The goal of this project is to explore a new principle for light trapping in solar cells. This approach could enable the design of solar cells that contain five times less silicon than conventional cells, while delivering the same amount of power. The concept is to couple two kinds of optical nanostructures: (1) very small metal particles, which are well known to scatter light strongly, and (2) patterned insulators that diffract light - the same phenomenon that gives rise to the colors of opals and butterfly wings. Theory predicts and preliminary experiments confirm that thin films of these combined structures are particularly good at light trapping. The challenge is to investigate the properties of different combinations, for which more efficient mathematical tools as well as fabrication methods must be developed, and to demonstrate that they can be integrated into solar cells in a manufacturable way. This project, with its multidisciplinary nature, engage graduate students in research that bridges topics in nanomaterials synthesis and patterning, solar cell module design, optical and electrical measurements, modeling, and mathematical algorithm development. Undergraduate honors students are also involved in this project at both Penn State and Delaware.