Dopant Diffusion through Selective Surface Regions to Improve Efficiency in Micro/Nano Textured Thin Solar Cells

We introduce a simple method to improve efficiency in micro/nano textured solar cells by diffusing a dopant through selective surface regions. This method is effective when the texture size is comparable to or smaller than the characteristic diffusion length. In this size regime, strong inhomogeneity in the dopant concentration often develops in the cells. In our case, the texture is an array of nanopyramidal dips on thin crystalline silicon solar cells. Our simulations for the texture show strong inhomogeneity in the dopant concentration along the textured surface. The strong inhomogeneity creates electrically inactive regions in the texture. With our doping method, our simulations show that the inhomogeneity can be significantly reduced to enhance charge collection efficiency. We confirm this prediction by directly measuring photovoltaic efficiencies of solar cells fabricated with and without using our doping method of selective diffusion. Our experiments demonstrate that our selective dopant diffusion enhances the efficiency from 12.5% to 13.3% for freestanding 15-μm-thick silicon solar cells textured with periodic nanopyramidal dips. Our method would be generally applicable for other micro/nano structures, semiconductor materials, and optoelectronic devices.