SBIR-STTR Award

A reduction in the cost of solar cell manufacturing is needed to accelerate penetration into the renewable energy market. To address this neeed, this project will develop a low-cost, photovoltaic solar module based on thin-film, CuInGaSe2 (CIGS) nanostructured materials, which are deposited by high-throughput roll-to-roll printing onto lightweight and flexible foil substrates. The development of this technology would permit solar modules to be manufactured at less than $1/Wp - equivalent to an electricity cost below the retail grid electricity price in most of the United States - an unprecedented level that would allow energy consumers to access far more economic and stable electricity pricing throughout the U.S. To reach a 10% or greater power conversion efficiency, Phase I will (1) synthesize high-purity, nanostructured ink components, (2) disperse these nanostructered components in solvent and dispersant, and (3) print this dispersion as a thin film coating onto a foil substrate moving in a roll-to-roll coating system. The dispersion’s composition, viscosity, and stability will be optimized to promote the formation of a stable semiconductor ink and support the deposition of a high-quality thin-film layer, which will serve as the active light-absorbing layer in the final photovoltaic device. Once a dispersion formulation has been established, printing the dispersion onto a moving substrate will require tuning of the key print parameters, including die angle and width, feed pressure, and wind and rewind tension.

Commercial Applications and Other Benefits as described by the awardee:
The low cost photovoltaic module should bridge the principal gap to bringing low-cost solar electricity to market. In addition, the technology also may encourage the further application of roll-to-roll electronics

Solar cells made from a copper-indium-gallium-diselenide (CIGS) absorber layer are more than 100X better at absorbing light than an equivalent absorber layer made from silicon; consequently, CIGS solar cells can be constructed as thin film devices, with less material usage and potentially less cost than conventional silicon-based solar cells. A thinner absorber layer also results in less cell fragility, providing an opportunity to further reduce costs by reducing the packaging surrounding the solar cell. Unfortunately, the production of CIGS-based solar cells is not cost effective. The central challenge in cost-effectively constructing a large-area CIGS-based solar cell is to ensure that the elements of the CIGS layer are within a narrow stoichiometric ratio, as required for the resulting cell or module to be highly efficient. However, achieving precise stoichiometric composition over relatively large substrate areas is difficult when using traditional vacuum-based deposition processes. In this project, nanoparticulate CIGS precursor materials will be printed onto low-cost metal foil substrates, and then a rapid thermal processing will be performed to convert the nanoparticulate coating into a CIGS absorber layer. By locking the appropriate stochiometry into the nanoparticulate precursor material, spatial uniformity will be ensured in the coated layers. Printing at high speed and high throughout will minimize solar cell cost. Phase I demonstrated that an efficient solar cell could be coated onto a foil using the new printing technology. Phase II will construct these foil-based solar cells with increased power conversion efficiency. The chemical composition of the light-absorbing layer will be modified to improve the optoelectronic performance of the device, and the performance characteristics of the devices will be determined.

Commercial Applications and Other Benefits as described by the awardee:
Thin-film, low cost, solar cells could be deployed on the roofs of both residential homes and commercial buildings, as well as utility-scale solar power plants. Such deployment would decrease the current U.S. dependence on foreign energy sources.