Vertically aligned Mg-doped GaN nanorods have been epitaxially grown on n-type Si substrate to form a heterostructure for fabricating p-n heterojunction photovoltaic cells. The p-type GaN nanorod/n-Si heterojunction cell shows a well-defined rectifying behavior with a rectification ratio larger than 10(4) in dark. The cell has a high short-circuit photocurrent density of 7.6 mAlcm2 and energy conversion efficiency of 2.73% under AM 1.5G illumination at 100 mW/cm2. Moreover, the nanorod array may be used as an antireflection coating for solar cell applications to effectively reduce light loss due to reflection. This study provides an experimental demonstration for integrating one-dimensional nanostructure arrays with the substrate to directly fabricate heterojunction photovoltaic cells.

Vertically aligned zinc oxide (ZnO) nanorod arrays coated with gold nanoparticles have been used in Schottky barrier solar cells. The nanoparticles enhance the optical absorption in the range of visible light due to the surface plasmon resonance. In charge separations, photoexcited electrons are transferred from gold nanoparticles to the ZnO conduction band while electrons from donor (I -) in the electrolyte compensate the holes left on the gold nanoparticles. The fill factors of the dye-free Schottky barrier cell reach a value of ∼0.50. However, after incorporation of N719 sensitizing dye, the open circuit voltage increases to 0.63 V from 0.5 V being measured for dye-sensitized solar cells based on the bare ZnO nanorods. The Schottky barrier at the ZnO/Au interface blocks the electron transfer back from ZnO to the dye and electrolyte, and thus increases the electron density at the ZnO conduction band. The efficiency of the gold-coated ZnO nanorod dye-sensitized solar cells is thus increased from 0.7% to 1.2%.