A Cheap Material Boosts Solar Cells by 50 Percent

Researchers have found a way to augment ordinary silicon solar cells with a material called a perovskite.

Solar energy is not cheap enough to compete with energy from fuels that cause greenhouse gas emissions.

Putting a new kind of photovoltaic material on top of a conventional solar cell can boost overall power output by half. Researchers at Stanford University added a type of material known as a perovskite to a silicon solar cell, validating an idea for cheaply increasing the efficiency of solar power that was first proposed several years ago.

Perovskites are materials with a particular crystalline structure. The perovskite used by the Stanford team contains relatively abundant and cheap materials including ammonia, iodine, and lead.

Materials scientists started demonstrating the photovoltaic potential of perovskites in 2009. Since then, different research groups have created perovskites with photovoltaic efficiencies comparable to those of many commercial solar cells. But perovskites also convert certain parts of the solar spectrum into electricity more efficiently than silicon, and vice versa, so the biggest efficiency gain may come from using perovskites to augment, rather than replace, the silicon in most solar cells (see “A Material that Could Make Solar Power ‘Dirt Cheap’ and “What’s Tech is Next for the Solar Industry?”). Now researchers at Stanford have shown that the idea can work.

One of the main challenges with pairing perovskite cells with silicon ones has been rendering the former transparent, so that light they don’t absorb can pass through to the silicon cells beneath. The perovskite solar cells made previously used an opaque material on the back to collect electrical current. The Stanford researchers developed a manufacturing method that involves producing a transparent electrode made of silicon nanowires.

The researchers took a cheap silicon solar cell with an efficiency of 11.4 percent and increased it to 17 percent by adding the perovskite cell.

Much work remains to be done before such cells are ready for market, however. Perovskite cells currently don’t last very long, and researchers are still trying to develop versions that don’t use lead, which is toxic.

The way light interacts with the two materials is also not yet well understood. When the Stanford group added perovskite to silicon solar cells whose efficiency was already 17 percent, for example, they measured a much smaller increase in power output, to 17.9 percent.

Even so, perovskites could be a boon for the solar industry. The researchers believe that perovskite-silicon cells will convert over 30 percent of the energy in sunlight into electricity. Such a boost would cut the number of solar panels for some installations almost in half, greatly lowering installation costs.

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