Heliatek’s panels are more efficient than the polymer-based ones, and are expected to last as long as a conventional silicon solar cell. The company uses short molecules called oligomers instead of polymers. Oligomers are inherently more stable, and can be deposited using a vacuum-deposition process that allows for precise control over the thickness and uniformity of the resulting films. That uniformity increases efficiency, and makes it easy to make multilayer solar cells that contain materials tuned to particular wavelengths of light—making the cells even more efficient.
Heliatek’s complete panels (a panel is a collection of cells wired together) convert 8 percent of the energy in light into electricity (polymer solar panels are 3 to 5 percent efficient). Conventional silicon solar panels are 14 to 15 percent efficient, but the Heliatek technology’s good performance in low light and high heat can make up for the lower efficiency, Séguillon says. In recent tests in Singapore, for example, Heliatek panels generated slightly more electricity over the course of a month than conventional silicon solar panels, he says.
Vacuum deposition is more expensive than printing, but Heliatek has introduced another innovation to help lower costs. Rather than making solar cells in batches on sheets of glass, it makes them continuously in a roll-to-roll process that deposits the materials on polyester.
To reach its ultimate cost goals, Heliatek will need to substantially improve its panels’ efficiency from 8 percent to 12 percent. This is possible because the company’s manufacturing process has allowed them to make what’s called a tandem solar cell, which has two layers for absorbing light and producing electrons. In the current design, both layers are tuned to convert the same wavelengths of light. But the company could also tune layers to different wavelengths and thus convert more of the solar spectrum. Heliatek is working with BASF to develop new absorber materials for such cells.
If the company does meet its cost goals, it still may be hard for it to compete head to head with companies making conventional solar panels. For one thing, banks are more willing to lend money for large solar power projects that use conventional panels, since they have proved workable in the field. In the long term, new solar companies may fare better by developing radically different solar panels that produce far more electricity than conventional silicon panels.