A 3D Nanostructure for Improved Solar-Cell Efficiency
By Ali Javey, Zhiyong Fan, Daniel Ruebusch, and Rehan Kapadia in SPIE, March 10 2010
Cost-effective photovoltaic (PV) technologies are the key for large-scale deployment of solar cells capable of producing clean energy. Although conventional planar crystalline PV cells can provide good efficiencies, they are not viable for large-scale deployment because of relatively high costs. On the other hand, inorganic and organic thin-film semiconductor-based PV cells have low material and fabrication cost, but their large-scale performance is poor.
Nanostructured materials grown with low-cost, bottom-up approaches usually have crystalline nature and, therefore, are promising candidates to achieve cost-effective PV cells. In addition, ordered nanostructures have demonstrated intriguing optical and electrical properties favoring photon broadband absorption and photocarrier collection. This suggests a potential route towards next-generation, high-efficiency PV devices. There has been extensive research into using nanostructured materials,1,2 such as silicon and gallium arsenide nanowires. Although these materials have been widely used for high-efficiency planar solar cells, they have high surface-recombination velocities and, thus, are not ideal materials for nanostructured PV cells.
We have developed a promising solar-cell module based on vertically oriented and spatially ordered cadmium sulfide (CdS) nanowires, or nanopillars (NPLs), embedded in a cadmium telluride (CdTe) thin film. The CdS/CdTe combination has relatively low surface-recombination velocity and so is ideal for taking advantage of the high surface/junction area to promote carrier-collection efficiency. Significantly, we have also achieved template-assisted growth of highly ordered NPL arrays on aluminum foil, avoiding costly epitaxial growth.