Spectral response characteristics of photovoltaic materials

The most efficient solar modules use multiple materials of slightly varying composition and electronic characteristics to convert different bandwidths of the solar spectrum into usable electricity. Cells made in this fashion generally require very expensive, high precision equipment leading to a high cost of the modules. It has been suggested that an optical system be used to disperse the sunlight into its constituent wavelengths (see Conte et. al. (1989)[22]) with different materials strategically placed under the appropriate bandwidth of light to produce higher efficiency, low cost modules. The proper selection and placement of materials requires detailed knowledge of the response of various materials to different wavelengths of light. Solid State Theory calculates this response through complicated mathematical models describing the band structure of the materials and the density of states for charge carriers. The research described herein defines this response through experiment. The experiment designed for this research examines the response of commercially available photovoltaic cells of various materials. Concentrated sunlight is passed through filters with known transmittance to illuminate a photovoltaic cell. The incident irradiance, and thereby the incident power, on the cell is recorded as well as the power output by the cell. These two powers are compared for each filter, and the results are plotted as efficiency vs. wavelength providing an experimental check for theoretical calculations. This experiment can be performed on any photovoltaic material of interest to determine optimal material selection and placement under the dispersed sunlight for a solar module. The combination of the methods developed in this research and the optics described in the paper by Conte et. al. can be used to produce an inexpensive, high efficiency solar module.