Tin Could Make Solar Cells Cheap, Efficient

Researchers have found a way to replace lead in perovskite-based solar cells. Their study shows that tin could be used as a low-cost and environmentally safe light-absorbing material in these cells.

Perovskite is used a solar energy harvester as it can convert up to 15 per cent of sunlight to electricity.

In the present study, researchers at Northwestern University and colleagues used tin along with perovskite to build the solar cells.

According to Mercouri G. Kanatzidis, lead author of the study, tin is a viable material and can bring the cost of solar cells down.

Their solid-state solar cell is essentially a sandwich of five layers. The first layer is glass followed by a layer of titanium dioxide; together they act as the electric front contact of the device.

Next is the tin perovskite, the light absorbing layer deposited in a nitrogen glove box. The transport layer is added to close the circuit and create a functioning cell. Researchers used a substituted pyridine molecule to create this structure. The last layer is made of gold. The entire device is about one to two microns thick

"Our tin-based perovskite layer acts as an efficient sunlight absorber that is sandwiched between two electric charge transport layers for conducting electricity to the outside world," said Robert P. H. Chang, a professor of materials science and engineering at the McCormick School of Engineering and Applied Science and a co-author of the study.

The team then exposed the device to simulated full sunlight. They found that their cell converted solar energy to electricity with an efficiency of 5.73 percent.

Kanatzidis said that the efficiency is good for a new type of solar cell.

"Other scientists will see what we have done and improve on our methods," Kanatzidis said in a news release. "There is no reason this new material can't reach an efficiency better than 15 percent, which is what the lead perovskite solar cell offers. Tin and lead are in the same group in the periodic table, so we expect similar results."

Several researchers are trying to find cheap, flexible inorganic materials that can be used in constructing low-cost, high-efficiency solar cells.

Previous research has shown that copper iodide could also be used in perovskite-based thin film solar cells. Perovskite material is itself relatively inexpensive, however, organic hole-conducting polymer, called spiro-OMeTAD is around ten times more expensive than gold or platinum. According to researchers, copper iodide could replace spiro-OMeTAD.

The study is published in the journal Nature Photonics.