FY2010 - Oak Ridge National Laboratory

Director’s R&D Fund—
Science for Extreme Environment: Advanced Materials and Interfacial Processes for Energy
nanocone surface. Preliminary photovoltaic experiments demonstrated that the nanocone-based solar cell
is functional under light illumination.
Information Shared
Lee, S. H., B. Smith, X. Zhang, S. S. Seo, Z. Bell, and J. Xu. 2010. “ZnO-ZnTe Nanocone
Heterojuctions.” Appl. Phys. Lett. 96, 193116 (selected for Virtual J. Nanoscience Sci. & Technol.).
05512
Low-Cost Materials and Manufacturing of CIGS Thin Film Solar Cells
Chad E. Duty, Michael Z. Hu, Ilia N. Ivanov, Gerald E. Jellison, Jr., Lonnie J. Love, Ji-Won Moon,
Chad M. Parish, and Tommy J. Phelps
Project Description
Today’s highest efficiency thin film solar cell converts solar energy to electricity with an efficiency
approaching 20%. The absorber layer is composed of an expensive and complex compound of copper–
indium–gallium diselenide (CIGS). A unique process has recently been developed at ORNL for producing
CIGS nanoparticles at an extremely low cost. Nanofermentation uses specialized bacteria to naturally
produce nanoparticles at moderate temperatures (~60°C), making it scalable for high-volume
manufacturing. Our objective is to demonstrate a process for the large-scale production of low-cost, highefficiency
CIGS thin film solar cells. To achieve this objective, we have divided activities into three main
tasks: (1) synthesize stoichiometric relevant CIGS nanoparticles, (2) develop a chemical passivation
technique for reducing the number of surface defects and providing nanoparticle stability, and (3) use
ORNL’s pulse thermal processing to consolidate CIGS nanoparticles into a continuous thin film solar cell
on a low-cost flexible substrate material. The primary objectives of the first year were to successfully
demonstrate the synthesis of CIGS nanoparticles, explore purification and passivation of the materials,
and conduct a preliminary investigation of depositing the materials on a substrate and consolidating the
particles into a thin film.
Mission Relevance
Thin film solar cells based on CIGS (Copper Indium Gallium Selenide) benefit from lower fabrication
cost and a significantly smaller amount of materials utilization (layer thickness of hundreds of nanometers
is needed for thin films compared to microns for silicon cells). Furthermore, the future of thin film solar
cells is highlighted by the recent breakthrough in their performance: CIGS research shows a conversion
efficiency approaching 20%. More attractive features of thin film solar cells are the low requirement on
material morphology. Even the most efficient thin film solar cells reported have a multicrystalline
structure with grain boundaries of micrometers. This indicates the possibility of utilizing materials with
low cost and imperfect quality. While current nanocrystal synthesis requires costly high temperatures and
vacuum, nanofermentation boasts synthesis at near-room temperatures using inexpensive solvents. This
project may create a paradigm shift in the synthesis of low-cost, highly efficient solar cells.
Results and Accomplishments
We have successfully bacterially synthesized multiple batches, from 10 mL to 1 L scale, of CIGS
nanoparticles with varying stoichiometry. CIGS (CuIn x Ga 1-x Se 2 ) and CIGSu (CuIn x Ga 1-x S 2 ) have been
synthesized from stock solutions having x = 0.2 to 0.6. The finding that Desulfovibrio desulfuricans
(G-20) can also produce CIGSu strengthened our patent application in that the application of
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