Solvent study solves solar cell durability puzzle — ScienceDaily

Rice University engineers say they have solved a long-standing mystery by creating stable, efficient solar panels from halide perovskites.

The right solvent design had to be found to deposit a 2D top layer of the desired composition and thickness without destroying the 3D bottom layer (or vice versa). Such a cell, with better stability, would convert more sunlight into electricity than either layer alone.

Chemical and biomolecular engineer Aditya Mohite and his lab at Rice’s George R. Brown School of Engineering reported Science their success in building thin 3D/2D solar cells that deliver 24.5% power conversion efficiency.

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

“This is really good for flexible, bifacial cells, where light comes in from both sides, and also for back-contact cells,” he said. “The 2D perovskites absorb blue and visible photons, and the 3D side absorbs near infrared.”

Perovskites are crystals with cubic lattices known to be efficient light collectors, but the materials tend to be stressed by light, moisture, and heat. Mohite and many others have worked for years to make perovskite solar cells practical.

The new advance, he said, largely removes the last major hurdle to commercial production.

“This is important on several levels,” Mohite said. “One of them is that it is inherently difficult to make a solution-processed bilayer when both layers are made of the same material. The problem is that they both dissolve in the same solvents.

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“If you put a 2D layer on top of a 3D layer, the solvent destroys the layer underneath,” he said. “But our new method solves that.”

Mohite said 2D perovskite cells are stable but less efficient at converting sunlight. 3D perovskites are more efficient but less stable. The combination of them brings together the best qualities of both.

“This leads to very high efficiencies because now, for the first time in this field, we are able to create layers with tremendous control,” he said. “It allows us to control the flow of charge and energy not only for solar cells, but also for optoelectronic devices and LEDs.”

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

Solution processing is widely used in industry and involves a variety of techniques – spin coating, dip coating, knife coating, slot coating, and others – to deposit material onto a surface in a liquid. When the liquid evaporates, the pure coating remains.

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The key is a balance between two properties of the solvent itself: its dielectric constant and the Gutmann donor number. The dielectric constant is the ratio of the material’s electrical permeability to its free space. This determines how well a solvent can dissolve an ionic compound. The donor number is a measure of the electron donating ability of the solvent molecules.

“If you find the correlation between them, you’ll find that there are about four solvents that you can use to dissolve and spin-on perovskites without destroying the 3D layer,” Mohite said.

He said their discovery should be compatible with roll-to-roll manufacturing, which typically produces 30 meters of solar cells per minute.

“This breakthrough leads, for the first time, to heterostructured perovskite devices containing more than one active layer,” said co-author Jacky Even, physics professor at the National Institute of Science and Technology in Rennes, France. “The dream of constructing complex semiconductor architectures with perovskites is about to come true. Novel applications and research into new physical phenomena will be the next steps.”

“This has implications not only for solar power, but also for green hydrogen with cells that can generate energy and convert it into hydrogen,” Mohite said. “It could also enable off-grid solar power for cars, drones, building-integrated photovoltaics, or even agriculture.”

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Rice graduate student Siraj Sidhik is the lead author of the work. Associated co-authors are exchange student Yafei Wang; graduate students Andrew Torma, Xinting Shuai, Wenbin Li and Ayush Agarwal; researchers Tanguy Terlier and Anand Puthirath; Matthew Jones, Norman and Gene Hackerman’s assistant professor of chemistry and materials science and nanoengineering; and Pulickel Ajayan, Benjamin M. and Mary Greenwood Anderson Professor of Engineering and Professor of Materials Science and Nanotechnology, Chemistry, and Chemical and Biomolecular Engineering. Additional co-authors are postdoctoral fellow Michael De Siena and Mercouri Kanatzidis, Professor of Chemistry at Northwestern University; Alumnus Reza Asadpour and Muhammad Ashraful Alam, the Jai N. Gupta Professor of Electrical and Computer Engineering, Purdue University; Postdoctoral Fellow Kevin Ho, Research Scientists Rajiv Giridharagopal and David Ginger, B. Seymour Rabinovitch Endowed Chair in Chemistry, University of Washington, Seattle; researchers Boubacar Traore and Claudine Katan from the University of Rennes; and Joseph Strzalka, physicist at Argonne National Laboratory.

The program of the Ministry of Energy Efficiency and Renewable Energy (0008843), the Academic Institute of France, the European Union’s Horizon 2020 research and innovation program (861985), the Office of Naval Research (N00014-20-1-2725), the Argonne National Laboratory (DE-AC02-06CH11357), the National Science Foundation (1626418, 1719797) and the Department of Energy (DE-SC00

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