MMaterialsgateNEWS 2018/04/09

Light ‘relaxes’ crystal to boost solar cell efficiency

Rice, Los Alamos discovery advances case for perovskite-based solar cells

Some materials are like people. Let them relax in the sun for a little while and they perform a lot better.

A collaboration led by Rice University and Los Alamos National Laboratory found that to be the case with a perovskite compound touted as an efficient material to collect sunlight and convert it into energy.

The researchers led by Aditya Mohite, a staff scientist at Los Alamos who will soon become a professor at Rice; Wanyi Nie, also a staff scientist at Los Alamos, and lead author and Rice graduate student Hsinhan (Dave) Tsai discovered that constant illumination relaxes strain in perovskite’s crystal lattice, allowing it to uniformly expand in all directions.

Expansion aligns the material’s crystal planes and cures defects in the bulk. That in turn reduces energetic barriers at the contacts, making it easier for electrons to move through the system and deliver energy to devices.

This not only improves the power conversion efficiency of the solar cell, but also does not compromise its photostability, with negligible degradation over more than 1,500 hours of operation under continuous one-sun illumination of 100 milliwatts per cubic centimeter.

The research, which appears this week in Science, represents a significant step toward stable perovskite-based solar cells for next generation solar-to-electricity and solar-to-fuel technologies, according to the researchers.

“Hybrid perovskite crystal structures have a general formula of AMX3, where A is a cation, M is a divalent metal and X is a halide,” Mohite said. “It’s a polar semiconductor with a direct band gap similar to that of gallium arsenide.

“This endows perovskites with an absorption coefficient that is nearly an order of magnitude larger than gallium arsenide (a common semiconductor in solar cells) across the entire solar spectrum,” he said. “This implies that a 300-nanometer thick film of perovskites is sufficient to absorb all the incident sunlight. By contrast, silicon is an indirect band gap material that requires 1,000 times more material to absorb the same amount of sunlight.”

Mohite said researchers have long sought efficient hybrid perovskites that are stable in sunlight and under ambient environmental conditions.

“Through this work, we demonstrated significant progress in achieving both of these objectives,” he said. “Our triple-cation-based perovskite in a cubic lattice shows excellent temperature stability at more than 100 degrees Celsius (212 degrees Fahrenheit).”

The researchers modeled and made more than 30 semiconducting, iodide-based thin films with perovskite-like structures: Crystalline cubes with atoms arranged in regular rows and columns. They measured their ability to transmit current and found that when soaked with light, the energetic barrier between the perovskite and the electrodes largely vanished as the bonds between atoms relaxed.

They were surprised to see that the barrier remained quenched for 30 minutes after the light was turned off. Because the films were kept at a constant temperature during the experiments, the researchers were also able to eliminate heat as a possible cause of the lattice expansion.

Measurements showed the “champion” hybrid perovskite device increased its power conversion efficiency from 18.5 percent to 20.5 percent. On average, all the cells had a raised efficiency above 19 percent. Mohite said perovskites used in the study were 7 percent away from the maximum possible efficiency for a single-junction solar cell.

He said the cells’ efficiency was nearly double that of all other solution-processed photovoltaic technologies and 5 percent lower than that of commercial silicon-based photovoltaics. They retained 85 percent of their peak efficiency after 800 hours of continuous operation at the maximum power point, and their current density showed no photo-induced degradation over the entire 1,500 hours.

“This work will accelerate the scientific understanding required to achieve perovskite solar cells that are stable,” Mohite said. “It also opens new directions for discovering phases and emergent behaviors that arise from the dynamical structural nature, or softness, of the perovskite lattice.”

The lead researchers indicated the study goes beyond photovoltaics as it connects, for the first time, light-triggered structural dynamics with fundamental electronic transport processes. They anticipate it will lead to technologies that exploit light, force or other external triggers to tailor the properties of perovskite-based materials.

Co-authors of the paper are research scientist Bo Chen, Rafael Verduzco, an associate professor of chemical and biomolecular engineering and of materials science and nanoengineering, and Pulickel Ajayan, chair of the Department of Materials Science and NanoEngineering, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering and a professor of chemistry, all of Rice; graduate student Reza Asadpour and Muhammad Ashraf Alam, the Jai N. Gupta Professor of Electrical and Computer Engineering, of Purdue University; research scientists Jean-Christophe Blancon, Sergei Tretiak and Wanyi Nie of Los Alamos; research assistant professor Constantinos Stoumpos and Mercouri Kanatzidis, the Charles E. and Emma H. Morrison Professor of Chemistry at Northwestern University; Jacky Even and Olivier Durand, professors of physics at the Institute of Electronics and Telecommunications of Rennes, France, and Joseph Strzalka, a physicist at Argonne National Laboratory.

Source: Rice University - 05.04.2018.

Investigated and edited by:

Dr.-Ing. Christoph Konetschny, Inhaber und Gründer von Materialsgate
Büro für Material- und Technologieberatung
The investigation and editing of this document was performed with best care and attention.
For the accuracy, validity, availability and applicability of the given information, we take no liability.
Please discuss the suitability concerning your specific application with the experts of the named company or organization.

You want additional material or technology investigations concerning this subject?

Materialsgate is leading in material consulting and material investigation.
Feel free to use our established consulting services

MMore on this topic

Nanoscale “grass” structures also enable smart glass that switches from hazy to clear in presence of water

Using nanoscale grass-like structures, researchers at the University of Pittsburgh, Pennsylvania have created glass that lets through a large amount of light while appearing hazy. This is the first time that glass has been made with such high levels of haze and light transmittance at the same time, a combination of properties that could help boost the performance of solar cells and LEDs. The glass exhibits another remarkable quality: It can be switched from hazy to clear by applying water. This could make it useful for creating smart windows that change haze or opacity to control the privacy of a room or to block glare from sunlight. “Switchable glass available today is quite expensive... more read more

See-through solar materials that can be applied to windows represent a massive source of untapped energy and could harvest as much power as bigger, bulkier rooftop solar units, scientists report today in Nature Energy.

Led by engineering researchers at Michigan State University, the authors argue that widespread use of such highly transparent solar applications, together with the rooftop units, could nearly meet U.S. electricity demand and drastically reduce the use of fossil fuels. “Highly transparent solar cells represent the wave of the future for new solar applications,” said Richard Lunt, the Johansen Crosby Endowed Associate Professor of Chemical Engineering and Materials Science at MSU. “We analyzed their potential and show that by harvesting only invisible light, these devices can provide a similar electricity-generation potential as rooftop solar while providing additional functionality... more read more

A new solar cell inspired by the compound eyes of insects could help scientists overcome a major roadblock to the development of solar panels based on a promising material called perovskite.

Packing tiny solar cells together, like micro-lenses in the compound eye of an insect, could pave the way to a new generation of advanced photovoltaics, say Stanford University scientists. In a new study, the Stanford team used the insect-inspired design to protect a fragile photovoltaic material called perovskite from deteriorating when exposed to heat, moisture or mechanical stress. The results are published in the journal Energy & Environmental Science (E&ES). “Perovskites are promising, low-cost materials that convert sunlight to electricity as efficiently as conventional solar cells made of silicon,” said Reinhold Dauskardt, a professor of materials science and engineering... more read more


Partner of the Week

Search in MaterialsgateNEWS

Books and products