Solar energy, while an attractive alternative energy source, has a big problem: the cells that are used to make conventional solar panels are often expensive to make. The solar cell is the essential component of the panel - the part that converts light into electricity. A cheap, durable alternative could be the catalyst for a new wave of commercial solar technology.

About 20 years ago, scientists developed a cheaper kind of solar cell, called the Gratzel cell, but this alternative suffers from its own problem. One of the essential parts of the Gratzel cell is an electrically conductive liquid that, unfortunately, has a tendency to eat away at the inside of the device, limiting its shelf life to around 18 months.

Now, Northwestern University scientists think they've solved this problem, according to a paper outlining a new kind of low-cost solar cell. The research was published Wednesday in the journal Nature.

What we have done is we completely replaced the way we think about the cell, said Northwestern chemist Mercouri G. Kanatzidis, a senior author of the paper.

In their design, Kanatzidis and his colleagues replaced the liquid electrolyte inside the cell with a thin metal film made from cesium, tin and iodine. The result is a stable, longer-lasting solar cell with about the same efficiency as the Gratzel cell.

Both the Gratzel cell and the new cell can convert around 10 percent of incoming light into electricity. Comparatively, a conventional solar cell made from silicon has a conversion rate of about 20 percent.

That lower efficiency isn't a barrier to producing solar cells for commercial use, according to co-author and Northwestern nanotechnologist Robert P.H. Chang.

Many solar cell applications in toys and electronics do not require high efficiency, he said.

The cell that Kanatzidis and Chang's team produced is only half a centimeter wide. The next step for commercial applications is to make them bigger - say, 10 centimeters by 10 centimeters. But Chang doesn't want to stop there.

The ultimate goal for us to make these cells flexible as well, he said.