Photovoltaic device applications of porous microcrystalline silicon

We report the fabrication of photovoltaic devices by the anodization of microcrystalline silicon films on single-crystal silicon substrates. The porosity of the films was varied from 20% to 60% by changing the anodization conditions. The influence of the porosity on the series resistance (R-s), the reflectance, and the spectral response of the devices was studied. In order to determine R-s, the current-voltage characteristics were analyzed, both in the dark and under illumination. We observed that the value of R-s increased from 3 to 100 Ohm and the value of the reflectance decreased from 24% to 7% when the porosity increased from 20% to 60%. The optimum device performance (fill factor of 0.53 and efficiency of 7.2%), which was achieved for a porosity of 40% and can be improved further, resulted from a trade-off between good electrical and optical properties. From optical beam-induced current images, the homogeneity of the devices was found to be excellent and no defects were detected. Our results indicate that the fabrication of commercial solar cells based on porous microcrystalline Si (PMSi) is possible. (C) 1998 Published by Elsevier Science B.V. All rights reserved.