Environmentally friendly solar cell advances push forward the ‘next big thing in photovoltaics’
Solar cell electronics appear to be getting friendlier on the environmental side of the spectrum. Northwestern University researchers have developed a new solar cell with good efficiency that uses tin instead of lead perovskite as the harvester of light.
This research advance provides a low-cost, environmentally friendly solar cell can be made easily using “bench” chemistry — no fancy equipment or hazardous materials.
“This is a breakthrough in taking the lead out of a very promising type of solar cell, called a perovskite,” said Mercouri G. Kanatzidis in a press announcement. He has expertise in dealing with tin. “Tin is a very viable material, and we have shown the material does work as an efficient solar cell,” he said.
Perovskite solar cells are being touted as the “next big thing in photovoltaics” and have reenergized the field.
The new solar cell uses a structure called a perovskite but with tin instead of lead as the light-absorbing material. Lead perovskite has achieved 15 percent efficiency, and tin perovskite should be able to match or surpass that figure.
Kanatzidis developed, synthesized and analyzed the material, then turned to Northwestern collaborator and nanoscientist Robert P. H. Chang to engineer a solar cell that worked well.
“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 Chang, a professor of materials science and engineering at the McCormick School of Engineering and Applied Science.
Details of the lead-free solar cell will be published May 4 by the journal Nature Photonics. Kanatzidis and Chang are the two senior authors of the paper.
Perovskite solar cells have only been around — and only in the lab — since 2008. In 2012, Kanatzidis and Chang reported the new tin perovskite solar cell with promises of higher efficiency and lower fabrication costs while being environmentally safe.
Structuring the layers
The solid-state tin solar cell is a sandwich of five layers, with each layer contributing something important. The first layer is electrically conducting glass, which allows sunlight to enter the cell. Titanium dioxide is the next layer, deposited onto the glass. Together the two act as the electric front contact of the solar cell.
The tin perovskite — the light absorbing layer — is then deposited.
On top of that is the hole transport layer, which is essential to close the electrical circuit and obtain a functional cell. This required Kanatzidis and his colleagues to find the right chemicals so as not to destroy the tin underneath. They determined what the best chemicals were — a substituted pyridine molecule — by understanding the reactivity of the perovskite structure. This layer also is deposited in the glove box. The solar cell is then sealed and can be taken out into the air.
A thin layer of gold caps off the solar-cell sandwich. This layer is the back contact electrode of the solar cell. The entire device, with all five layers, is about one to two microns thick.
The researchers then tested the device under simulated full sunlight and recorded a power conversion efficiency of 5.73 percent.
Source: AAAS EurekAlert