Spectral Modification of Diffuse Rear Reflector Layers for Higher Efficiency in Silicon Solar Cells

Abstract

Global climate change and energy cost are two of the most important challenges facing modern societies. Solar photovoltaic energy production is one of the most promising avenues by which to address these problems. However solar photovoltaic energy is still too expensive relative to other technologies despite over thirty years of advancement. The work described in this thesis involves improved means for the trapping of light in solar cells and has broad application to almost all existing photovoltaic platforms including silicon (over 95% of all photovoltaic generation is silicon-based). In particular titanium oxide diffuse rear reflector systems were examined to determine the gains possible relative to the non-reflector and planar mirror rear reflectors presently in popular use. The preparation procedures and materials used were chosen for cost competitive advantage. The rear contacts of commercially obtained silicon solar cells were chemically removed and alternative contacts applied. The resultant solar cells were measured using a calibrated simulated solar illumination and the quantum efficiency measurement as a function of wavelength was determined. Significant gains in solar cell long wavelength spectral response were found when diffuse rear reflector contacts were applied. For example, the quantum efficiency of a solar cell with a diffuse rear reflector peaked at 29.4% at 1100 nm as compared to 12% for a non-reflective rear contact and 14% for that for the case of the as-received commercial solar cell. Work to further improve the diffuse rear reflector is expected to generate even greater gains.