The world’s most efficient solar cells are twice as efficient as the ones people put on their roofs, but hardly anyone uses them because the semiconductor materials they’re made of are so expensive. That could be about to change.

Ali Javey, professor of electrical engineering and computer sciences at the University of California at Berkeley, has found a far cheaper way to manufacture these better-performing semiconductors. This advance could lower the cost of high-efficiency solar cells, potentially making them as cheap as conventional ones. Javey says the new process could be a “game changer” for solar cells.

Improving the efficiency of affordable solar cells will be essential for making solar power competitive with fossil fuels. Fewer cells would be needed, reducing costs for materials and installation, a large share of the total cost of solar power. Early tests suggest solar cells made from the materials would have an efficiency of about 25 percent, which is far better than conventional silicon solar cells, which are less than 18 percent efficient. And a preliminary analysis by the National Renewable Energy Laboratory suggests Javey’s cells could be made as cheaply as conventional ones.

The most efficient solar cells available today are made from materials called III-V semiconductors, a group that includes gallium arsenide and indium phosphide. Making solar cells from these materials normally means starting with expensive crystals of the semiconductor material, then exposing the crystals to vapors that produce the thin films need for a solar cell.

Javey’s process instead grows thin films for solar cells on top of a cheap material—glass or a sheet of metal. The vapors used in the process are cheaper than those normally used, and they’re used far more efficiently, reducing waste.

The process is still at an early stage though. Javey is just starting to make solar cells made from the new materials, and says there’s a lot of work to do to optimize the process.

However, the materials might serve as the basis for an advanced type of solar cells made of multiple semiconductor materials. Such “multi-junction” solar cells efficiently absorb and convert light from more wavelengths of light, and in the lab they have reached efficiencies of well over 40 percent.

Jessica Adams, a senior R&D engineer at Microlink Devices, a company that makes high-efficiency solar cells for niche applications, such as military drones, says Javey’s solar cells are “some way off from being a commercial product.”

But Adams says Javey has “demonstrated a way that we may be able to make solar cells out of indium phosphide relatively cheaply, with the potential to get very high efficiency.”