Porous Polycrystalline Silicon Thin Film Solar Cells: Final Report, 24 May 1999--24 May 2002

The initial focus of this project was to build on previous work performed in our group and investigate the use of porous polycrystalline silicon (Psi) as an active material in a solar cell to take advantage of potential bandgap tuning, light trapping, and blue-harvesting photoluminescence effects. However, through our work on various substrate materials, we have found that the electricalcharacteristics of thick (several microns) PSi layers needed for active devices are extremely sensitive to the substrate doping profiles and crystalline morphology. This sensitivity makes reproducibility difficult even in a well-controlled research environment, and therefore, prospects for commercial thick-film PSi devices are limited. We have now focused our investigation on the use of thin PSilayers for antireflective coating applications. By isolating these layers in the heavily doped surface region of a solar cell, the electrical properties of the p-n junction are relatively unaffected. Provided that good electrical contacts can be made to the material under the porous layer, the electrical properties of the PSi film are not critical, and only the optical properties need to beoptimized.