Science 339, 1057–1060 (2013)

Solar cells based on an array of semiconductor nanowires instead of a continuous planar design can, in principle, reduce the amount of material required to construct a photovoltaic module. However, so far, the performance of nanowire cells has been considerably poorer than that of their flat counterparts. Now, Jesper Wallentin and co-workers from Sweden, Germany and China have fabricated an InP nanowire array cell with a power conversion efficiency of 13.8%, which is comparable to those of the best planar InP devices. Although the 180-nm-diameter InP nanowires in their device cover only about 12% of the cell's surface, resonant light-trapping effects give an optical-to-photocurrent conversion efficiency that is six times higher than that predicted by simple ray optics. Furthermore, their nanowire cell's open-circuit voltage, a critical parameter in solar cells, is superior to that of the planar design, reaching 0.906 V, despite a 30 times higher surface-to-volume ratio. The research team says sample tests showed that the efficiency of their best devices degraded less than 0.5% over a period of six months. They also point out that the design should be scalable to wafer-sized cells and may also be useful for constructing photodetectors.