Chinese researchers have taken what they say is a major step forward for the development of a new generation of solar cells.
Manufacturers have long used silicon to make solar panels because the material was the most efficient at converting sunlight into electricity. But organic photovoltaics, made from carbon and plastic, promise a cheaper way of generating electricity.
A new study led by Chen Yongsheng from Nankai University in north China’s Tianjin, has proved that the organics have the potential to be just as efficient as silicon.
“Low charge mobility of organic materials limited the active layer thickness and light absorption efficiency,” Chen said. His team used tandem cells, which are put together by different layers of organic materials, to address the problem.
“Different layers of the tandem cells can absorb different wavelengths of light. That means you can use sunlight more effectively and achieve a higher power conversion rate,” Chen said.
With further optimization of the materials, it is expected that the OPVs can achieve similar power conversion efficiency as traditional solar panels, according to the researchers.
Commercial solar photovoltaics usually covert 15-22% of sunlight, with a world record for a silicon cell of 26.6% reached in Japan in 2016. Organics have long lingered at around half this rate, but this year has seen some major leaps forward.
In April researchers were able to reach 15% in tests. Now this new study pushes that beyond 17% with the authors saying that up to 25% is possible. This is important because according to estimates, with a 15% efficiency and a 20 year lifetime, organic solar cells could produce electricity at a cost of less than 7 cents per kilowatt-hour.
In 2017, the average cost of electricity in the US was 10.5 cents per kilowatt-hour, according to the US Energy Information Administration.
One of the things that has made OPV less efficient in the past is the fact that the organic materials have loosely bound molecules which can trap electrons and slow down the generation of electricity. So researchers have tried to get around this by putting different layers of material together in a what’s termed a tandem cell approach.
“Tandem cell means you have two devices built together in the same structure,” said one of the authors, Dr Yongsheng Chen, from Nankai University in Tianjin, China.
“We have two layers of active materials, each layer can absorb different wavelengths of light. That means you can use sunlight in the wider wavelengths or more efficiently and this can generate more current.”
The researchers think the technology is not far from commercial production in less than 5 years.
Flexible, printed solar cells offer a wide range of possibilities. They can work indoors and they can be made semi-transparent, so they could be incorporated into windows and generate power during daylight.
They offer huge potential for buildings as they are lightweight so might be ideal for deploying on the roofs of houses in developing countries where structures might not suit heavy silicon. They could be used on the roofs of cars, and in clothes, even in glasses to charge your phone while you are out and about.
“This looks a remarkable result to me,” said Dr Artem Bakulin, from Imperial College London.
“The development of such new materials with previously unthinkable properties allowed them to achieve the reported record efficiency and, in general, makes OPV technology much more promising.”
Dr Feng Gao from Linköping University in Sweden also believes the new paper is significant.
“This work is a very important contribution to organic solar cells and will certainly inspire new developments in the field,” he said by email.
“The tandem organic solar cells with record efficiencies in this work indicate great potential of organic solar cells for practical applications.”