Andrew Torma, an Applied Physics graduate student at Rice University, validates the electronic structure of a 2D/3D perovskite solar cell. (Credit: Jeff Fitlow/Rice University)

It took finding the appropriate solvent design to use a 2D top layer of desired composition and thickness without destroying the 3D bottom one (or vice versa). Such a cell would turn more sunlight into electricity than either layer by itself, with higher stability.

In Science, chemical and biomolecular engineer Aditya Mohite and his lab at Rice University‘s George R. Brown School of Engineering reported their success at constructing thin 3D/2D solar cells that deliver an influence conversion efficiency of 24.5%.

That’s as efficient as most commercially available solar cells, Mohite said.

“This is de facto good for flexible, bifacial cells where light is available in from each side and likewise for back-contacted cells,” he said. “The 2D perovskites absorb blue and visual photons, and the 3D side absorbs near-infrared.”

Perovskites are crystals with cubelike lattices known to be efficient light harvesters, however the materials are inclined to be stressed by light, humidity and warmth. Mohite and plenty of others have worked to make perovskite solar cells practical for years.

The brand new advance, he said, largely removes the last major roadblock to business production.

“This is important at multiple levels,” Mohite said. “One is that it’s fundamentally difficult to make a solution-processed bilayer when each layers are the identical material. The issue is that they each dissolve in the identical solvents.

“Whenever you put a 2D layer on top of a 3D layer, the solvent destroys the underlying layer,” he said. “But our recent method resolves this.”

Mohite said 2D perovskite cells are stable, but less efficient at converting sunlight. 3D perovskites are more efficient but less stable. Combining them incorporates one of the best features of each.

“This results in very high efficiencies because now, for the primary time in the sector, we’re in a position to create layers with tremendous control,” he said. “It allows us to regulate the flow of charge and energy for solar cells, optoelectronic devices, and LEDs.”

The efficiency of test cells exposed to the lab equivalent of 100% sunlight for greater than 2,000 hours “doesn’t degrade by even 1%,” he said. Not counting a glass substrate, the cells were about 1 micron thick.

Solution processing is widely utilized in industry and incorporates a variety of techniques—spin coating, dip coating, blade coating, slot die coating and others—to deposit material on a surface in a liquid. When the liquid evaporates, the pure coating stays.

The bottom line is a balance between two properties of the solvent itself: its dielectric constant and Gutmann donor number. The dielectric constant is the ratio of the electrical permeability of the fabric to its free space. That determines how well a solvent can dissolve an ionic compound. The donor number is a measure of the electron-donating capability of the solvent molecules.

“For those who find the correlation between them, you’ll find there are about 4 solvents that will let you dissolve perovskites and spin-coat them without destroying the 3D layer,” Mohite said.

He said their discovery needs to be compatible with roll-to-roll manufacturing that typically produces 30 meters of solar cell per minute.

“This breakthrough is leading, for the primary time, to perovskite device heterostructures containing a couple of lively layer,” said co-author Jacky Even, a professor of physics on the National Institute of Science and Technology in Rennes, France. “The dream of engineering complex semiconductor architectures with perovskites is about to return true. The subsequent steps will probably be novel applications and the exploration of latest physical phenomena.”

“This has implications not only for solar energy but in addition for green hydrogen, with cells that may produce energy and convert it to hydrogen,” Mohite said. “It could also enable non-grid solar for cars, drones, building-integrated photovoltaics and even agriculture.”

Rice graduate student Siraj Sidhik is lead creator of the paper.

Publication Referenced within the Article:

Siraj Sidhik et al., Deterministic fabrication of 3D/2D perovskite bilayer stacks for durable and efficient solar cells, Science (2022). DOI: 10.1126/science.abq7652.

This text was written by the team at Rice University.


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