The fast-growing area of perovskite PV technology continues to grab headlines, with the latest news coming from Stanford University. In a paper published this week, the Stanford researchers have outlined a method for perovskite tandem cells in which a transparent electrode is applied to the base semiconductor layer. A technique to apply a silver nanowire electrode to the perovskite layer was one of the key breakthroughs.
The Stanford researchers were able to boost the efficiency of an 11.4% silicon cell to 17%, through the application of the perovskite semiconductor layer. The perovskite itself had an efficiency of 12.7%. On a CIGS cell with an efficiency of 12.7% the resultant perovskite tandem cell achieved 18.5% efficiency.
Given the fragility of the perovskite material, the Stanford team had to develop a method by which electrodes could be attached between the semiconductor stacks. The solution was to apply the transparent electrodes to plastic and then to the cell using a pressure tool.
"We used a sheet of plastic with silver nanowires on it," said Stanford graduate student Colin Bailie, a co-author of the study. "Then we built a tool that uses pressure to transfer the nanowires onto the perovskite cell, kind of like a temporary tattoo. You just need to rub it to transfer the film."
One of Bailies collaborators Michael McGehee said that it was the first time a perovskite cell with two transparent electrodes had been produced.
The Stanford teams findings were published in the journal Energy & Environmental Science this week.
The long-term stability of perovskite remains a barrier to its immediate commercial rollout. Co-lead author of the most recent Stanford paper McGehee confirmed this while commenting on the findings.
"Silicon is a rock," said McGehee, a professor of materials science and engineering at Stanford. "You can heat it to about 600 degrees Fahrenheit, shine light on it for 25 years and nothing will happen. But if you expose perovskite to water or light it likely will degrade. We have a ways to go to show that perovskite solar cells are stable enough to last 25 years.
McGehee said that his vision is to see low cost perovskite tandems with efficiencies of to 25% or even as high as 30% in five-to-ten years.