Printable electric circuits [Image source: Wikimedia Commons]
The US solar cells manufacturer, Triton Solar, has just signed a $100 million agreement to open a manufacturing facility in the Indian state of Karnataka, aiming to start production at the site from August 2016. The company announced the decision on 14th December, having already, in April, planned to construct a facility in Madhya Pradesh. Triton Solar is based in New Jersey and specializes in printable solar cells that are powered by nanotechnology and are produced by a patented printing technique. As well as operating in outdoor conditions, the cells can also produce solar energy from ambient lighting, without any need for direct sunlight.
Few other companies or organizations have embraced printable solar thin-film so far, despite the technology hitting the headlines two years ago in 2013. In that year, the Australian Victorian Organic Solar Cell Consortium (VICOSC), part of the Australian Commonwealth Scientific and Industrial Research Organization (CSIRO), demonstrated a scale-up of printing processes for organic solar cells which enabled them to facilitate continuous printing of bulk heterojunction (BHJ) solar cells using a 30 cm wide substrate. Several demonstration modules were developed for evaluation. These were dye sensitized cell (DSC) modules that can be printed on to a number of substrates, including plastic, glass or steel. They operate through the ability of the ink to capture sunlight and convert it into electricity. This could potentially enable them to be integrated into a range of items, such as smartphone, tablet or laptop cases. However, at present, they are 10 times less efficient than standard silicon.
In March 2014, a team of British scientists from the National Physical Laboratory (NPL) in Middlesex also developed printable solar cells. These can operate on gloomy days when there is little sunlight available and the potential applications include integration into the material of coats or bags where they could be used to charge mobile devices.
Another company involved in developing the technology is Eight19 which is using organic semiconductor materials that are sourced from abundant, potentially low-cost, materials. These semiconductors have a strong light absorption ability, around 100 times stronger than that of silicon, and they can be produced from a solution under ambient conditions which in turn makes the material ultra-thin. This also means that they can be printed using continuous roll-to-roll printing and coating processes thereby reducing costs. The printing devices used to achieve this are already available. They can print material at several tens to several hundreds of metres per minute and are commonly used for producing packaging and high quality coatings.
Given that thin-film is extremely lightweight, there is no need for any roof reinforcement and the ability to print the cells in a range of colours means that they could potentially be far less obtrusive than standard silicon solar panels. The auto industry is also becoming interested in printable thin-film solar, with a view to potentially installing solar PV on car roofs where they would help to charge the vehicle’s electrical circuits.
This technology is still at an early stage of development so it will be a while before we see it deployed commercially. However, progress in this area is being driven forward by universities around the world and also by large chemical companies. Very often this requires some kind of partnership arrangement (Eight19 works with Cambridge University and various material development companies).
The story doesn’t end there however, because printable organic solar cells now have a rival technology – perovskite solar cells - which have reached 20 percent efficiency as opposed to just 10 percent.
Perovskite began to attract attention from the solar sector about five years ago. It is a material that contains lead, iodine and an organic component. When it was first being researched, perovskite could only reach 3 percent efficiency, but over just five years that has now jumped to 20 percent, double that of the printable organic thin-film mentioned earlier. According to Michael Grätzel, a solar researcher at the Ecole Polytechnique in Lausanne, Switzerland, writing in an edition of Nature Materials, the rise of metal halide perovskite in the solar sector stunned the PV community. Fiona Scholes, an organic photovoltaics expert at the CSIRO, speaking to Cosmos Magazine, described the development as “without a doubt the biggest advance in organic solar cells.”
Perovskite tin solar cells [Image source: University of Oxford Press, Flickr]
According to materials engineer Jinsong Huang at the University of Nebraska, the key to perovskite’s ability to generate electricity is its internal structure which enables electrons to easily reach the electrode in a printed perovskite solar cell. However, in order to compete effectively with silicon it would still need to reach around 25 percent efficiency, something that may be possible within the next five years.
There are some downsides to Perovskite solar cells, such as sensitivity to moisture and the fact that it contains lead, thereby becoming a source of toxicity if broken. However, Huang believes that perovskite cells could be optimized in order to make it more stable while other researchers are working on ways to substitute the lead content for something less harmful.
Fiona Scholes believes that printable solar cells will become “a key part of the renewable energy mix” in the years ahead. It’s certainly true, given the need to do something about climate change by decarbonizing the world’s energy supply, that we need to investigate as many avenues as we can.
Increasingly, printable solar cells look like they are going to become an important part of that overall energy toolkit.
Written by Robin Whitlock