MATERIALS | PHOTOVOLTAICS
can be supported on flexible substrates that are lightweight and colour-tuneable,” said Hatton. “Conventional silicon solar cells are fantastic for large scale electricity generation in solar farms and on the roofs of buildings, but they are poorly matched to the needs of electric vehicles and for integration into windows on buildings – which are no longer niche applications. Organic solar cells can sit on curved surfaces and are very lightweight and low profile.”
Above: Kaust researchers have combined silicon solar cells with a polymer backing to create devices that combine flexibility with high efficiency
Right: In Kaust’s Solar Centre, researchers have used tiny tungsten disulphide flakes to improve the performance of organic solar cells
1% contact UK researchers have found that a truism of creating OPVs is not necessarily correct – determining that electrodes can be far less conductive than previ- ously assumed. Scientists at the University of Warwick in the UK have found that the electrodes in organic solar cells actually only need around 1% of their surface area to be electrically conductive to be fully effective. It has long been assumed that 100% of the surface of each electrode should be electrically conductive to maximise the efficiency of charge extraction. The findings mean that a wider choice of materials could be used at the interface between the electrodes and the light-harvesting organic semiconductor layers. The research is reported in Advanced Functional Materials. The researchers developed a model electrode whose surface area could be systematically changed. They found that when as much as 99% of its surface was electrically insulating, it performs as well as if 100% of the surface were conducting – pro- vided the conducting regions are not too far apart. The researchers say that composites of insula- tors and conducting nanoparticles – such as carbon nanotubes, graphene fragments or metal nanopar- ticles – could have great potential for this purpose, offering better device performance or lower cost. “There is a fast-growing need for solar cells that
36 FILM & SHEET EXTRUSION | May 2020
Stretching silicon A key advantage of OPVs is that, despite their lower efficiencies, they are more flexible than traditional silicon solar cells – so can be used in a variety of new applications. However, researchers at the King Abdullah University of Science and Technology (Kaust) in Saudi Arabia have managed to combine silicon solar cells with a highly elastic polymer backing to create cells that combine flexibility with high efficiency. The researchers have devised a way to turn rigid silicon into solar cells that can be stretched by 95%, while retaining an energy efficiency of 19%. The research was published in Advanced Energy
Materials. The researchers took a commercially available, rigid silicon panel and coated the back of it with a stretchable, biocompatible silicone elastomer called Ecoflex. The team used a laser to cut the rigid cell into multiple silicon ‘islands’, which were held together by the elastomer backing. Each silicon island remained electrically connected to its neighbours via contacts that ran the length of the flexible solar cell. The team initially made rectangular silicon pieces
that could be stretched to around 54%, but beyond this point the stretching led to diagonal cracks within the brittle silicon islands. The team then tried a diamond pattern before settling on triangles. “Using the triangular pattern, we achieve world
record stretchability and efficiency,” said Muham- mad Mustafa Hussain, professor of electrical engineering at Kaust, who led the research. The researchers plan to use the material to power a multi-sensory artificial skin that they have devel- oped. Making ‘stretchy’ solar panels is also a target. “These solar cells can be mainly stretched in one
direction, and we are working to improve the multi-directional stretching capability,” said Hussain.
Elsewhere in Kaust, researchers in the Solar
Centre are using microscopic flakes of tungsten disulphide – just a few atoms thick – to improve the performance of organic solar cells. The team, led by Thomas Anthopoulos, says the
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