Optical Downconverting Nanomaterials for Enhanced Photovoltaic Efficiency

For photovoltaic cells used to power space missions, such as those based on silicon, CuInGaSe2, and III-V materials, optical-to-electrical conversion efficiency is reduced by at least 25% because the energy of solar photons in excess of the band gap of the semiconductor absorber is lost. The excess photon energy is converted to heat. In addition, the quantum efficiencies of solar cells tend to degrade for high energy photons due to surface recombination effects. Optical down-conversion has been suggested as a method to recoup this lost energy, providing an increase in the theoretical single junction photovoltaic conversion efficiency from 30.9% to 39.6%. If substantial gains in PV efficiency could be achieved with a thin film coating of an efficient two photon downconverting layer, it would have a tremendous benefit not only to NASA payload burden, but also the the economics of terrestrial solar cells. However, the absence of materials with suitable time constants for the relevant electronic processes has hindered the realization of this method. Our proposed solution, being developed by the University of Arizona, is to use the unique optical properties of nanocrystals to produce efficient downconverting emitter materials. Phase I will entail synthesis of the new materials at EIC Laboratories and their optical evaluation at Arizona, with a goal of demonstrating the first practical examples of such a thin film material.