Engineering nanostructures for solar energy conversion

Technology to efficiently harness solar energy to generate electricity (Solar-Cells) and carbon-free hydrogen (H2) fuel (Solar-fuels) has the potential to ensure our long-term energy sustainability and alleviate global warming issues. However, the practical solar-energy conversion efficiencies, especially in the solar-fuels are far below their theoretical limits. In the solar-energy conversion devices, three fundamental processes, i.e., light absorption, charge transport and transfer, determines the efficiency and they are closely connected to the photoelectrode design on the nanometer scale. Our goal in this project is to develop more efficient nanostructures of photoelectrodes by engineering the nanostructure based on three processes and to demonstrate their enhanced solar-energy conversion efficiency. The novel nanostructures we developed can be leveraged to other materials and energy conversion devices such as Li-ion batteries, supercapacitors and electrochromics to greatly improve their efficiencies.

Branched Nanorods array (B-NRs) as a novel photoelectrode nanostructure: A hierarchically branched TiO2 nanorod structure which serves as a model architecture for efficient photoelectrochemical devices was synthesized. It simultaneously offers a large contact area with the electrolyte, excellent light-trapping characteristics, and a highly conductive pathway for charge carrier collection, thereby it showed enhanced PEC water splitting performance.

Flame synthesis of WO3 nanowires for efficient photoelectrochemical water-splitting: Atmospheric flame vapor deposition synthesis has the ability to control the vapor pressure of tungsten oxide over a wider range of conditions than conventional synthesis methods, resulting in an increased packing density of WO3 nanowires. This leads to better light absorption and higher PEC water splitting performance compared to WO3 nanowires synthesized by other methods.

Hybrid Si Microwire and Planar Solar Cells; Hybrid Si microwire (radial junction) and planar solar-cell was designed and a 11.0% efficiency was demonstrated by passivating top surface and p-n junction with thin-a-Si:H and intrinsic poly-Si films, respectively. Comparing to the planar cells of the identical layeres, the hybrid solar cell showed increased light absorption and charge-carrier collections.

Selected Publications

  1. "Flame Synthesis of WO3 Nanotubes and Nanowires for Efficient Photoelectrochemical Water-Splitting", P. M. Rao, I. S. Cho, and X. L. Zheng, Proc. Combust. Inst., accepted (2012)
  2. "Branched TiO2 Nanorods for Photoelectrochemical Hydrogen Production ", I. S. Cho, Z. Chen, A. J. Forman, D. R. Kim, P. M. Rao, T. F. Jaramillo, and XL. Zheng , Nano Lett., 11, 4978-4984 (2011)
  3. "Hybrid Si Microwire and Planar Solar Cells: Passivation and characterization ", D. R. Kim, C. H. Hwan, P. M. Rao, I. S. Cho, and X. L. Zheng, Nano Lett., 11, 2704-2708 (2011)