A Waferscale Si Wire Solar Cell Using Radial and Bulk P-n Junctions

Silicon nanowires (NWs) and microwires (MWs) are cost-effectively integrated on a 4-inch wafer using metal-assisted electroless etching for solar cell applications. MWs are periodically positioned using low-level optical patterning in between a dense array of NWs. A spin-on-doping technique is found to be effective for the formation of heavily doped, thin n-type shells of MWs in which the radial doping profile is easily delineated by low voltage scanning electron microscopy. Controlled tapering of the NWs results in additional optical enhancement via optimization of the tradeoff between increased light trapping (by a graded-refractive-index) and increased reflectance (by decreasing areal density of NWs). Compared to single NW (or MW) arrayed cells, the co-integrated solar cells demonstrate improved photovoltaic characteristics, i.e. a short circuit current of 20.59 mA cm(-2) and a cell conversion efficiency of ∼ 7.19% at AM 1.5G illumination.