Rice University engineers say they have solved a long-standing puzzle about making stable, efficient solar panels from halide perovskites.
It was necessary to find the right solvent design to apply a 2D top layer of desired composition and thickness without damaging the 3D bottom (or vice versa). Such a cell would convert more sunlight into electricity than either layer alone, with better stability.
Chemical and biomolecular engineer Aditya Mohite and his lab at Rice’s George R. Brown School of Engineering reported on Science their success in fabricating thin 3D/2D solar cells that provide a power conversion efficiency of 24.5%.
This is as efficient as most commercially available solar cells, Mohite said.
“This is really good for flexible, bifacial cells where light enters from both sides, as well as back-contact cells,” he said. “The 2D perovskites absorb blue and visible photons and the 3D side absorbs the near infrared.”
Perovskites are crystals with cubic lattices that are known to be efficient light harvesters, 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 many levels,” Mohite said. “One is that it is fundamentally difficult to create a solution-processed bilayer when both layers are the same material. The problem is that 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,” 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. Their combination incorporates the best features of both.
“This leads to very high yields because now, for the first time in the 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 “does not degrade by 1%,” he said. Not counting a glass substrate, the cells were about 1 micron thick.
Solution processing is widely used in industry and incorporates a number of techniques — spin coating, dip coating, blade coating, slot die coating, and others — to deposit material onto a surface in a liquid. When the liquid evaporates, the clear coating remains.
The key is the balance between two properties of the solvent itself: its dielectric constant and its Gutmann donor number. The dielectric constant is the ratio of the electrical permeability of the material 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 find that there are about four solvents that allow you to dissolve perovskites and spin-coat them without destroying the 3D layer,” Mohite said.
He said their discovery should be compatible with roll-to-roll manufacturing that typically produces 30 meters of solar cells per minute.
“This discovery leads, for the first time, to heterostructures of perovskite devices containing more than one active layer,” said co-author Jacky Even, professor of physics at the National Institute of Science and Technology in Rennes, France. “The dream of engineering complex semiconductor architectures with perovskites is about to become a reality. New applications and exploration of new physical phenomena will be the next steps.”
“This has implications not only for solar energy 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, photovoltaics built into buildings or even agriculture.”
Rice graduate student Siraj Sidhik is the paper’s lead author. Rice-affiliated co-authors are exchange student Yafei Wang; graduate students Andrew Torma, Xinting Shuai, Wenbin Li, and Ayush Agarwal; research scientists Tanguy Terlier and Anand Puthirath. Matthew Jones, the Norman and Gene Hackerman Assistant Professor of Chemistry and Materials Science and Nanoengineering. and Pulickel Ajayan, the Benjamin M. and Mary Greenwood Anderson Professor of Engineering and professor of materials science and nanoengineering, chemistry, and chemical and biomolecular engineering. Other co-authors are postdoctoral researcher Michael De Siena and Northwestern University chemistry professor Merkouri Kanatzidis. graduate student Reza Asadpour and Muhammad Ashraful Alam, Purdue University’s Jai N. Gupta Professor of Electrical and Computer Engineering. postdoctoral researcher Kevin Ho, researcher Rajiv Giridharagopal, and David Ginger, the B. Seymour Rabinovitch Endowed Chair in Chemistry at the University of Washington, Seattle. researchers Boubacar Traore and Claudine Katan of the University of Rennes; and Joseph Strzalka, a physicist at Argonne National Laboratory.
The program of the Department of Energy Efficiency and Renewable Energy Sources (0008843), the Institut Academie de France, the Horizon 2020 research and innovation program of the European Union (861985), the Office of Naval Research (N00014-20-1-2725), the National Argonne Laboratory (DE-AC02- 06CH11357), the National Science Foundation (1626418, 1719797), and the Department of Energy (DE-SC00