Optically improved solar cell using tapered silicon nano wires

We suggest a cost-efficient way to fabricate the silicon nanowires (SiNWs) for commercial solar cell applications. Vertically aligned SiNWs arrays were prepared on a four-inch silicon wafer using a simple room temperature approach, i.e., metal-assisted electroless etching. Further chemical etching using a 30 wt% aqueous KOH solution at 20°C was performed for adjusting the areal density of NWs while tapering the nanowire morphology. During KOH etching process, we achieved separation of each NW from the bunched NW by tapering the SiNW morphology, resulting in a strong enhancement of broadband optical absorption. As electroless etching time increases, the optical crossover feature was observed in the tradeoff between enhanced light trapping (by graded-refractive index during initial tapering) and deteriorated reflectance (by decreasing the areal density of NWs during later tapering). The tapered N W solar cell shows the superior photovoltaic characteristics such as ~23 % increase in a short circuit current and 80 % increase in conversion efficiency compared to a bunched NW.