Scientists from Pennsylvania State University, Shaanxi Normal University, Hubei University and the US Army Combat Capabilities Development Command have designed a semi-transparent perovskite solar cell that reached 19.8%, and 28.3% in a tandem cell stacked on top of a silicon-heterojunction device. The device is based on a film of gold just a few atoms thick, grown using an innovative seeding method, which is both highly conductive and transparent.
The team investigated, in their new study, a new method to grow a very thin, continuous layer of gold onto a perovskite solar cell as the top electrode layer. Despite the fact that gold is a rare and expensive material, the group is convinced its approach offers an alternate, efficient route to fabricating perovskite and tandem solar cells.
'We've shown we can make electrodes from a very thin, almost few atomic layers of gold,' said Shashank Priya, associate vice president for research and professor of materials science and engineering at Penn State. 'The thin gold layer has high electrical conductivity and at the same time it doesn't interfere with the cell's ability to absorb sunlight.'
Key to the electrode layer was the use of a chromium seed layer, which serves to spread the gold evenly into a continuous film, with high light transmittance and conductivity. 'Normally, if you grow a thin layer of something like gold, the nanoparticles will couple together and gather like small islands,' explained Dong Yang, assistant research professor of materials science and engineering at Penn State. 'Chromium has a large surface energy that provides a good place for the gold to grow on top of, and it actually allows the gold to form a continuous thin film.'
The group then incorporated this gold electrode into a perovskite solar cell, which it measured at 19.8% efficiency, and further incorporated the perovskite cell into a tandem device, stacked on top of a silicon heterojunction cell. This device reached an efficiency of 28.3%, improving on the HJT cell's initial 23.3% efficiency.
The group also mentioned that the perovskite cells it fabricated are 'stable and maintain high efficiencies over time in laboratory tests', but did not elaborate further.