Scientists at the Okinawa Institute of Science and Technology Graduate University (OIST) have resolved a fundamental weakness in a promising solar technology known as Perovskite Solar Cells, or PSCs. Their innovations appear to improve both the devices’ stability and scalability in one fell swoop and could be key to moving PSCs to market.
Third-generation solar cells efficiently convert sunlight into usable electricity and cost less energy to manufacture than old-school silicon cells. PSCs, in particular, have garnered the attention of science and industry thanks to their low cost and high efficiency. Though their performance is promising in lab tests, the devices still suffer from low stability and cannot be produced commercially until they’re built to last.
“We need solar modules that can last for at least 5 to 10 years. For now, the lifetime of PSCs is much shorter,” said Dr. Longbin Qiu, first author of the paper and a postdoctoral scholar in the OIST Energy Materials and Surface Sciences Unit, led by Prof. Yabing Qi. The study, published online in Advanced Functional Materials, supports prior evidence that a commonly used material in PSCs, called titanium dioxide, degrades the devices and limits their lifetime. The researchers replaced this material with tin dioxide, a stronger conductor without these degrading properties. They optimized their method of applying tin dioxide to produce stable, efficient and scalable PSCs.
In experiments, the researchers found that tin dioxide-based devices showed lifetimes over three times longer than PSC devices using titanium dioxide. “Tin dioxide can give users the device performance they need,” said Qiu. An Improved Design PSCs consist of layered materials, each with a specific function. The “active layer,” made from perovskite materials, absorbs incoming sunlight in the form of particles called photons. When a photon strikes a solar cell, it generates negatively-charged electrons and positively-charged holes in the active layer. Scientists control the flow of these electrons and holes by sandwiching the active layer between two “transport materials,” thus creating a built-in electrical field.
To help usher electrons in the right direction, many PSCs include an “electron transport layer.” Most PSCs employ titanium dioxide as their electron transport layer, but when exposed to sunlight, the material reacts with perovskite and ultimately degrades the device. Tin dioxide stands as a viable replacement for titanium dioxide, but before this study, it had not been successfully incorporated into a large-scale device.