A new solar cell efficiency record has been achieved by a startup CA-based company called Alta Devices. Previously unknown, the Santa Clara firm brags an efficiency of 28.2 percent for their gallium-arsenide solar cell, a number 2 percent higher than last year’s previous record, and could eventually bring down the costs of solar power to make it compete with coal and gas.
The researchers at Alta Devices improved the gallium arsenide’s inherent properties, making it “almost an ideal solar-cell material.” In any solar cell, when photons hit its surface, some of them get trapped and transformed into electrons, entering the electric circuit, and others get re-transformed into light or just heat the cell – a process called “decay.” If the electrons that produce light could be reabsorbed by the cell to generate another electron, the overall efficiency could be raised in such a cell.
Gallium arsenide (GaAs), the material that the researchers chose, has the property of producing more light than absorbing heat. Alta Devices treated their GaAs material so that a photon has about 100 chances of being reabsorbed. They treated the material chemically, filling the eventual cracks, so it doesn’t have the tendency of transforming the electrons into heat, thus wasting them. Hence the greater probability of the electrons being transferred into usable electricity.
The Alta Devices researchers also improved the production technology of their solar cell. They did that by implementing a technique called epitaxial liftoff, rather than chemical vapor deposition, and allowed for the semiconductor to be less pretentious than it had to be so far using the old technology. The epitaxial liftoff had been invented by Eli Yablonovitch, one of Alta Devices’ founders.
