MATERIALS | PHOTOVOLTAICS
Right: Chalmers University researchers have designed a window film – using a new molecule – that captures solar energy in the day and releases it at night
inexpensive materials help to channel charge in the devices, and so raise efficiency. When light hits the solar cell, it frees electrons
from the material and leaves positively charged ‘holes’. Electrons and holes are gathered by different layers of the device, and delivered to the cell’s electrodes to generate a current. The leading hole transporter is a polymer called PEDOT:PSS. However, it is acidic and absorbs moisture from the air – which degrades other materials in the solar cell. The team has developed a hole-transporting layer made from 2D flakes of tungsten disulphide. The researchers used ultrasound to tear the flakes off powdered tungsten disulphide suspended in a mixture of water and ethanol. This method is inexpensive and easy to scale up, and the flakes can be spread onto an electrode using a simple, widely used process called spin-coating. The team made several OPVs this way, and the best had a power conversion efficiency of 17%. “Our immediate goal is to push the efficiency of
our organic solar cells well beyond 17% and toward our theoretically predicted limits,” said Anthopoulos. “We also aim to study the stability of these high-efficiency organic solar cells.” Details of the work were published in Advanced
Materials.
Hot and cold Researchers at Chalmers University in Sweden have developed a window film – using a specially designed molecule – that could even out the extremes of temperature from day to night. When the molecule is struck by the sun’s rays, it
captures photons and simultaneously changes its form – it is isomerised. When the sun stops shining on the window film, the molecules release heat for up to eight hours after the sun has set. The research is published in the journal Advanced Science. “The aim is to create a pleasant indoor environ-
38 FILM & SHEET EXTRUSION | May 2020
ment – even when the sun is at its hottest – without consuming any energy or having to shut ourselves behind blinds,” said Kasper Moth-Poulsen, profes- sor of chemistry at the university, who is leading the research. The molecule is part of a concept the research
team calls Most (Molecular Solar Thermal Storage). Previously, it was presented as an energy system for houses based. In that case – after the solar energy had been captured by the molecule – it could be stored for an extended period, such as from summer to winter. The researchers realised that they could shorten the step to application by optimising the molecule for a window film. At dawn, when the film has not absorbed any solar energy, it is yellow or orange. These colours are at the opposite end of the spectrum to blue and green – which is the light spectrum that the molecule captures from the sun. When this hap- pens, it loses its colour and becomes transparent. As long as the sun is shining on the film it captures energy, so that less heat penetrates the film and enters the room. At dusk, when there is less sunlight, heat is released – and it slowly returns to its yellow shade, ready to capture sunlight again the following day. “Airports and office complexes should be able to
reduce their energy consumption while creating a more pleasant climate with our film, since the current heating and cooling systems often do not keep up with rapid temperature fluctuations,” he said.
CLICK ON THE LINKS FOR MORE INFORMATION: �
www.tu-dresden.de �
www.uhasselt.be �
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www.riken.jp/en �
www.warwick.ac.uk �
www.kaust.edu.sa �
www.chalmers.se
www.filmandsheet.com
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