• A 1 cm2 monolithic perovskite-silicon tandem solar cell.

A 1 cm2 monolithic perovskite-silicon tandem solar cell. (Photo : Rongrong Cheacharoen/Stanford University)

For all the hype surrounding them, existing silicon solar cells are stubbornly inefficient, converting just 25 percent of solar energy into electricity. The remainder is lost as heat.

This situation hasn't changed in decades because of the insistence by solar panel makers in using cheap silicon to build their solar panels.

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Researchers at the Massachusetts Institute of Technology (MIT) and Stanford University, however, have developed a novel prototype device that combines "perovskite" with traditional silicon solar cells into a two-terminal "tandem" device.

The team said their new tandem cells have the potential to achieve significantly higher solar energy conversion efficiencies compared to the standard single-junction silicon solar cells. They discovered that stacking perovskite atop a conventional silicon solar cell forms a tandem able to improve the solar cell's overall efficiency, or the amount of sunlight a solar cell can convert into electricity.

The prototype tandem solar cell developed demonstrated an open-circuit voltage of 1.65 volts, which was its best-case scenario, said the team.

Its 13.7 percent power-conversion efficiency still leaves much to be desired, however. Researchers noted this is a first step in overcoming problems that occur when pairing silicon with perovskite, a cheap and abundantly available crystalline material that can easily be produced in labs.

Eventually, a new generation of tandem solar cells will have efficiencies greater than the peak 25.6 percent of standard silicon cells, said Phys.org.

The team concentrated on developing tandem solar cells because there was big room for improvement in their cost and market penetration.

Tandem solar cells are currently being used in solar panels, but aren't that popular, with a puny market share of 0.25 percent compared to silicon solar cells' 90 percent. That's because making tandem solar cells using existing technology is terribly expensive.

"Despite having higher efficiency, tandems are traditionally made using expensive processes, making it difficult for them to compete economically," said Colin Bailie, a Ph.D. student at Stanford and an author on the new paper.

The team's tandem approach focuses on keeping costs low and "integrates perovskite solar cells monolithically-building them sequentially in layers-onto a silicon solar cell, without significant optical or electrical losses, by using commonly available semiconductor materials and deposition methods".