The majority of high-performance solar cells under development use a combination of materials including perovskite and spiro-MeOTAD. These cells are cheaper than traditional silicon-based solar cells and their efficiency has been increasing significantly in the past few years. But perovskite, which is the layer that converts sunlight to electricity, degrades quickly.
Nanosized pinholes in the spiro-MeOTAD layer may be creating easy pathways for water and other gas molecules in air to diffuse through the thin film and degrade the perovskite. The appearance of these pinholes appear to be related to how the spiro-MeOTAD layer is usually made.
A solution is spin-coated onto a base layer to create a thin film a tiny fraction of the thickness of a human hair. Another preparation method, vacuum evaporation, does not produce the pinholes, but is less convenient to use.
Zafer Hawash, a PhD student at OIST who discovered the pinholes, said:
“No one has really mentioned this. I started realizing it was something important to report, to let people know these pinholes exist and that we should get rid of them to get better lifetime.”
The researcher are looking into how they can eliminate the pinholes while still keeping the cost low, perhaps by tweaking preparation process or adding other ingredients.
The research took place at Okinawa Institute of Science and Technology Graduate University.