Engineers from Rice University claim to have found a solution to a long-standing problem with producing stable, effective solar panels from halide perovskites. Aditya Mohite, a chemical and biomolecular engineer, and his team reported building thin 3D/2D solar cells with a 24.5 percent power conversion efficiency. According to Mohite, that is as efficient as the majority of commercial solar cells.
To apply a 2D top layer with the desired composition and thickness without destroying the 3D bottom one, the proper solvent design had to be found (or vice versa). Such a cell would be more stable and produce more electricity from sunlight than either layer could on its own.
“This is really good for flexible, bifacial cells where light comes in from both sides and also for back-contacted cells. The 2D perovskites absorb blue and visible photons, and the 3D side absorbs near-infrared,”
Mohite said.
Perfecting Practical Perovskites
The manufacture of high-efficiency solar cells with layers of 2D and 3D perovskites. Credit: Jeff Fitlow/Rice University
Perovskites are cubic crystals with efficient light-harvesting properties, but light, humidity, and heat can stress the materials. Making perovskite solar cells practical has been the focus of years of work by Mohite and numerous others.
This latest development essentially removes the last significant impediment to commercial production.
“This is significant at multiple levels. One is that it’s fundamentally challenging to make a solution-processed bilayer when both layers are the same material. The problem is they both dissolve in the same solvents. When you put a 2D layer on top of a 3D layer, the solvent destroys the underlying layer. But our new method resolves this,”
Mohite said.
Combining 2D With 3D
Efficient, stable bilayer perovskite solar cells are closer to commercialization. The cells are about a micron thick, with 2D and 3D layers.
Credit: Jeff Fitlow/Rice University
2D perovskite cells, according to Mohite, are stable but less effective at converting sunlight. Although less stable, 3D perovskites are more effective. Combining them unlocks their best qualities, leading to very high efficiencies.
“Because now, for the first time in the field, we are able to create layers with tremendous control. It allows us to control the flow of charge and energy for not only solar cells but also optoelectronic devices and LEDs,”
said Mohite.
The effectiveness of the perovskite photovoltaics test cells exposed for more than 2,000 hours to the lab equivalent of 100% sunlight does not decline by even 1%, he stated. The thickness of the cells, excluding the glass substrate, was about 1 micron.
Solution Processing The Solution
Solution processing is widely used in industry and includes a variety of techniques to deposit material on a surface in a liquid, including spin coating, dip coating, blade coating, slot die coating, and others. The pure coating is left behind when the liquid evaporates.
Both the solvent’s dielectric constant and Gutmann donor number must be in balance to achieve the desired result. The material’s electrical permeability to its free space is measured by the dielectric constant.
Accordingly, a solvent’s ability to dissolve an ionic compound is determined. A measurement of the solvent molecules’ ability to donate electrons is the donor number.
“If you find the correlation between them, you’ll find there are about four solvents that allow you to dissolve perovskites and spin-coat them without destroying the 3D layer,”
Mohite said.
Multilayer Perovskite Heterostructures
It should be possible to use their discovery with roll-to-roll production, which typically produces 30 metres of solar cells per minute.
“This breakthrough is leading, for the first time, to perovskite device heterostructures containing more than one active layer. The dream of engineering complex semiconductor architectures with perovskites is about to come true. Novel applications and the exploration of new physical phenomena will be the next steps.”
co-author Jacky Even, physics professor at the National Institute of Science and Technology in Rennes, France, said.
This has implications for green hydrogen, which uses cells that can generate energy and convert it to hydrogen, as well as solar energy.
“It could also enable non-grid solar for cars, drones, building-integrated photovoltaics or even agriculture,”
Mohite said.
