Semprius, a startup that makes minuscule solar cells capable of capturing concentrated sunlight without costly cooling systems, announced this week that it had made the world's most efficient solar panel.

The company's solar panels use tiny solar cells made of gallium arsenide. The record-breaking solar module contains hundreds of such cells, each about the width of a line drawn by a ball-point pen, arranged under lenses that concentrate sunlight 1,100 times.

Gallium arsenide is far better at absorbing sunlight than silicon, the material used in most solar cells, but it's also more expensive. Furthermore, although concentrated solar modules use less semiconducting material, they usually require expensive optics, cooling systems, and tracking systems to keep them aimed at the sun. Semprius's microscaled solar cells are inherently much better at dissipating heat, making them cheaper.

Semprius's modules have another advantage: whereas a silicon solar cell only efficiently absorbs a narrow band of sunlight, the solar cells in this module are made of three layers of gallium arsenide, each modified to convert a different part of the solar spectrum into electricity.

Tests by a third party certified the efficiency of Semprius's solar panel at 33.9 percent, marking the first time any solar module has been able to convert more than one-third of the sunlight that falls on it into electricity. Conventional silicon solar panels typically convert less than 15 percent of light into electricity, and the record for a silicon solar panel is 22.9 percent. The previous record for any solar panel was 32 percent, Semprius says.  

One-off, experimental modules have achieved higher efficiencies, but Semprius's record-setting module is designed for commercial use. It was made with the same type of equipment that the company is installing in a small factory in Henderson, North Carolina, that is expected to open this summer. "It's a good indication of the efficiencies our customers can expect," says Joe Carr, Semprius's CEO.

Semprius's process forms tens of thousands of tiny solar cells on a single wafer of gallium arsenide, and uses chemical etching and a robotic system to transfer each layer to an inexpensive substrate. The same gallium arsenide wafer can be reused many times, reducing costs. The approach is based on a method for transferring small electronics from a wafer to other substrates that was developed by John Rogers, a professor of materials science and engineering at the University of Illinois at Urbana-Champaign.