Wafer-Scale Growth of Silicon Microwire Arrays for Photovoltaics and Solar Fuel Generation

Abstract

Silicon microwire arrays have recently demonstrated their potential for low-cost, high-efficiency photovoltaics and photoelectrochemical fuel generation. A remaining challenge to making this technology commercially viable is scaling up of microwire-array growth. We discuss here a technique for vapor–liquid–solid growth of microwire arrays on the scale of six-inch wafers using a cold-wall radio-frequency heated chemical vapor deposition furnace, enabling fairly uniform growth over large areas with rapid cycle time and improved run-to-run reproducibility. We have also developed a technique to embed these large-area wire arrays in polymer and to peel them intact from the growth substrate, which could enable lightweight, flexible solar cells with efficiencies as high as multicrystalline Si solar cells. We characterize these large-area microwire arrays using scanning electron microscopy and confocal microscopy to assess their structure and fidelity, and we test their energy-conversion properties using a methyl viologen (MV $^{2+/+}$ ) liquid junction contact in a photoelectrochemical cell. Initial photoelectrochemical conversion efficiencies suggest that the material quality of these microwire arrays is similar to smaller (∼1 cm $^2$ ) wire arrays that we have grown in the past, indicating that this technique is a viable way to scale up microwire-array devices.