Lightweight, flexible solar cells are great for some niche applications—such as powering drones—where heavier, conventional solar panels won’t work. They could also help reduce the cost of installation, which is one of the biggest parts of the cost of solar power, by making solar panels easier to install. But to take on power from fossil fuels, such cells need to be both far more efficient and cheaper to make.

Some Swiss researchers have taken a step in that direction, announcing a record solar cell efficiency for a type of flexible solar cell that could be cheap to make. But commercializing the technology will be difficult.

The researchers announced that they’ve set a new record for flexible copper indium gallium selenide (CIGS) solar cells, a type of solar cell that has the potential for low costs because it can be made quickly with relatively small amounts of material. CIGS cells, if made on a flexible plastic or metal foil, can also be flexible, unlike conventional silicon solar panels, which are heavy and rigid. But CIGS cells aren’t as efficient as conventional silicon ones, making it hard for the technology to compete. Efficiency is the most powerful lever for reducing solar power costs. Improved efficiency reduces the number of solar panels needed for a given installation, saving on the cost of panels and labor.

The researchers demonstrated solar cells with an efficiency of 20.4 percent, which is far better than the roughly 13 percent efficiency of flexible CIGS cells used in commercial applications such as solar rooftop shingles. It’s also better than typical silicon solar cells, which are roughly 16 percent efficient (higher cost, premium silicon solar cells can have efficiencies as high as 24 percent).

Hitting a record efficiency in the lab, however, is a far cry from achieving those efficiencies on a production line. It’s common for production cells to be 30 percent less efficient than a company’s champion cells. The researchers will also need to contend with competition from companies such as Alta Devices, which have achieved higher efficiencies for flexible solar cells using different materials (see “Alta Devices: Finding a Solar Solution”). Alta Devices’s best cells are 28.8 percent efficient, but it needs to lower its manufacturing costs to compete with conventional solar panels.