The characteristics of well-aligned silicon nanowire (SiNW)/poly(3,4-ethylenedioxy-thiophene): poly(styrenesulfonate) (PEDOT) heterojunction solar cells with varying nanowire lengths are investigated. PEDOT adheres on the hydrophilic n-type silicon nanowire surface to form a core-sheath heterojunction structure through the solution process. Such a structure increases the area of heterojunctions and shortens the carrier diffusion distance, and therefore, it greatly increases carrier collection efficiency. The cells exhibit stable rectifying diode behavior. Compared to the cells without a nanowire structure, the series resistance of the SiNW/PEDOT cell decreases from 60.42 Ω cm 2 to 1.47 Ω cm 2 , and the power conversion efficiency improves from 0.08% to 5.09%. The SiNW/ PEDOT solar cell harvests photons from 400 nm to 1100 nm and a maximum incident phototocurrent conversion efficiency of ∼32% at 700 nm.

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Zinc oxide ͑ZnO͒ nanowire arrays with controlled nanowire diameter, crystal orientation, and optical property were prepared on sol-gel ZnO-seed-coated substrates with different pretreatment conditions by a hydrothermal method. The vertical alignment, crystallinity, and defect density of ZnO nanowire arrays are found to be strongly dependent on the characteristics of the ZnO thin films. Field-emission scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction, and room temperature photoluminescence were applied to analyze the quality of the ZnO nanowire arrays. The annealing temperature of the ZnO thin film plays an important role on the microstructure of the ZnO grains and then the growth of the ZnO nanowire arrays. The x-ray diffraction results indicate that the thin film annealed at the low temperature of 130 °C is amorphous, but the thereon nanowire arrays are high-quality single crystals growing along the c-axis direction with a high consistent orientation perpendicular to the substrates. The as-synthesized ZnO nanowire arrays via all solution-based processing enable the fabrication of next-generation nanodevices at low temperature.