Just two years away: cheap, easy to make, 3rd generation solar cells

In 2018, the long-promised “third generation” of solar cells will be ready to come to market. These are very different from the solar panels we see around us today. Transparent, lightweight, flexible and highly efficient, they will be able to be applied to windows, metal, polymers (as in cladding) or cement, effectively turning buildings into energy generators.

They can work in lower light conditions than current solar technologies, and don’t have to face the sun.

The technology is known as perovskite solar cells. Recently, a research team headed by Professors Michael Grätzel and Anders Hagfeldt at the Ecole Polytechnique Fédérale de Lausanne established a new world record efficiency for the cells, with a certified conversion efficiency of 21.02 per cent, increasing from 3.8 per cent in 2009, making this the fastest-advancing solar technology to date.

With low production costs, many start-up companies are promising modules on the market by 2017.

Dyesol Limited is one such company focused on commercialising these cells. Dyesol has been around for many years, longer than most of its competitors, and has secured several key patents in the field.

Three years ago it switched its research and development from dye-sensitised technology to perovskite because of its advantages.

Based in Australia, its chief executive, Richard Caldwell (above), recently released a levelised cost of energy study (which enables comparison with the market price of other energy technologies). This demonstrated costs of between 9.6 and 12 Australian cents per kilowatt-hour for the panels when manufactured and utilised at a relatively small scale. This compares to around 10-11 cents for conventional solar – about the same, but before mass production.

At the end of last year Caldwell reached an agreement with the Australian Renewable Energy Agency to receive $450,000 funding support to progress the technology towards scalable manufacture and mass commercialisation. ARENA has established a production cost of 25 cents per watt.

“The payback period for installation is a matter of a few months, as they are less energy intensive to produce than the current (usually silicon based), which take several years,” Caldwell says.

“This is extremely exciting, as it allows us to transition to a clean energy society without any subsidies from the government.

“BIPV – building-integrated photovoltaics, in other words putting solar power generation on the surface of buildings – is the holy grail of the industry and because perovskite is ultra-thin it can easily be incorporated in buildings,” he said. “But that’s longer term. We will first produce a free-standing unit for market entry, then integrated.”

The company publishes quarterly updates of progress to demonstrate progress. Caldwell says that its next landmark later this year is “the production of panels about one metre square”, with countries like Turkey partnering to produce them.

“By 2018 we hope to be in mass production of this new product.”

The first product will feature a glass substrate, allowing light through to the interior of the building. The following year, metal-printed panels will be on the market, the company says.

Australian support

Dr Richard Corkish, chief operating officer at the Australian Centre for Advanced Photovoltaics, which has been responsible for many of the improvements in silicon solar panels the world uses today, told the ABC: “Most of the important advances in solar cell work in the past has been in making incremental improvements on the same old technology that [was] invented way back in the 1950s, but [is] now much, much better.

“[Perovskite] has captured the excitement of the whole photovoltaic research community. This material might in the future offer an alternative to silicon for the main solar cell material. Our research partners – Monash University and the University of Queensland in particular – are at the forefront of this area in Australia.”

Caldwell says “the new political regime in the Australian government is more favourable to us and the Turkish government is also very supportive.”

He welcomed Bill Gates’ recognition of the technology during the Paris climate talks, when Gates joined 27 other wealthy investors to start a new investment fund called the Breakthrough Energy Coalition, to push more public and private sector funds to clean energy technology.

Gates called PSC “disruptive” and said: “When people start talking about perovskites, painted solar applications etcetera, a lot of it is down to the physics, so the majority of the money will flow through the fund.”

The technology

The most commonly studied perovskite absorber is methylammonium lead trihalide, which uses a halogen atom such as iodine, bromine or chlorine.

Unlike traditional silicon cells, which require expensive, multistep processes conducted at high temperatures (>1000 °C) in a high vacuum in special clean room facilities, the organic-inorganic perovskite material can be manufactured with simpler wet chemistry techniques in a traditional lab environment.

Methylammonium and formamidinium lead trihalides have been created using a variety of solvent techniques and vapour deposition techniques, both of which have the potential to be scaled up with relative feasibility. These techniques reduce the need to use so much polluting solvents.

Issues yet to be resolved are around stability, as the material can degrade, reducing its efficiency.

Dyesol is developing and testing this. Its most recent newsletter, published last week, announced that a test strip passed 1000 hours at 85°C with a loss of under 10 per cent. That is still a lot, so work is underway to reduce this deterioration with different types of encapsulation. To be fair, early silicon panels suffered from a similar problem.

A related challenge is cheap and environmentally friendly electricity storage, enabling solar electricity to be used also at night.

But for now, having been heralded for a long time, very cheap solar power that lets every building or object coated with it generate electricity is now within reach.

David Thorpe is the author of:

• Solar Technology: The Earthscan Expert Guide to Using Solar Energy for Heating, Cooling and Electricity


• The ‘One Planet’ Life: A Blueprint for Low Impact Development


• Energy Management in Buildings: The Earthscan Expert Guide


• Energy Management in Industry: The Earthscan Expert Guide


• Sustainable Home Refurbishment: The Earthscan Expert Guide to Retrofitting Homes for Efficiency

Could this solar power breakthrough kill off nuclear power?

New breakthroughs in solar technology have been announced which could mean a complete game changer in the way electricity is generated.

The technology involves printing a new type of solar cell onto building materials, such as steel and glass, and allowing them to generate electricity.

The chief announcement is the result of joint ventures between Australian company Dyesol and, in Wales, Tata Steel, and in America Pilkington Glass.

Researchers are being cautious as to the timescale, but it is estimated that in about five years time industrial production on a large scale could begin.

Speaking at a recent conference on solar power, James Durrant of the Department of Chemistry and Energy Futures Lab at Imperial College London, said “If just 10% of Tata's annual steel output were coated with DSSC, this would represent the output capacity equivalent to a 1GW nuclear power station per year".

Dye-sensitised solar cells (DSSC)

These 'dye-sensitised solar cells' (DSSC) employ a photoelectrochemical system similar to that employed by plants to capture solar energy.

In the manufacturing process, a nanocrystalline titanium oxide film plus a sensitiser dye are printed onto glass, polymer or steel and covered with glass or plastic.

Modules made from the cells currently have efficiencies up to 8% depending upon a compromise between stability and cost, but cells in the lab have reached 13% efficiency, and Dyesol is confident they can reach 10% under mass-production conditions in five years time.

DSSC has the following advantages over conventional silicon photovoltaic modules:

• it can output a constant operating voltage in all light conditions, including low light and dappled conditions typical of urban and city environments, making it an ideal renewable resource for closely packed buildings
• it has an optimum working temperature of 40o-50oC, unlike silicon PV, which becomes less efficient at higher temperatures
• it uses little energy in manufacture due to the low temperature processes and absence of high vacuum technology needed for second generation technologies (thin film PV)
• due to the nanoparticulate nature of the titanium dioxide, modules can generate electricity from light from any direction, removing the need for them to be pointed directly at the sun
• it can be produced in a range of natural colours and light transmission effects including transparent, translucent or opaque
• it uses no polluting dopant
• the ability to produce a constant operating voltage in all light conditions
• it is ideal for integrating into building cladding.

The race to mass production

Many companies are racing to produce this type of cell at an industrial scale.

Notable organic and dye-sensitized solar cell (DSSC) developers include, beside Dyesol: Eight19, EPFL, G24i, Heliotek, Konarka (printing large molecule polymers), Mitsubishi, Peccell, Plextronics, Solarmer, SolarPress and SolarPrint.

SolarPrint is also developing nanomaterials and processes to print the cells onto polymer substrates. Other researchers are experimenting with printing on fibreglass.

Eight19 Limited has raised $5 million from the Carbon Trust and Rhodia to develop plastic organic solar cells. The name "Eight19" refers to the time it takes sunlight to reach the earth.

The reason why Dyesol is a front-runner is because of its teamwork with Pilkington and Tata Steel. These joint ventures are already ahead of the game in terms of applying coatings on a continuous roll, as opposed to a batch process, output.

Existing coatings applied to steel include galvanising layers to prevent rust, colours, anti-static, and self cleaning layers, all of which are guaranteed for 40 years.

Tata's Rodney Rice, speaking from their DSSC Demonstration Roof at the PV Accelerator in Shotton, North Wales, where the process is being tested, told Energy and Environmental Management, "we use high speed large scale coating, on steel rolls 1.5m wide, put through at a speed of 200 metres per minute.

"This adds up to 200 million square metres of steel per annum, of which half ends up on buildings. If we assume 10 to 20% of this is on a roof or wall and the PV is operating at between 8 and 10% efficiency, then this will easily equate to 1 GW per year.

“We are developing our knowledge of printing coatings to printing the ability to generate electricity and to steel. It uses reasonably straightforward materials which are reliable, simple to apply and easy to scale up as there is no vacuum and fewer people involved.

"This means it has the perfect attributes for the mass-market and the technology will work well in northern Europe where there are large surface areas of roof tops."

The Dyesol-Tata partnership has obtained considerable support from the Welsh Government, and over the last four years has spent ￡11 million on R&D.

“Lowering the price is the objective and we are now developing processes that will allow us to do this in manufacture," continued Rodney.

"Initially steel rolls will be one metre wide with 10% efficiency leading to a production of 400 MW per year," he said.

Tata use coated steel and coated polymer electrodes, whereas Pilkington are using coated glass electrodes.

In America, the Pilkington-Tata joint venture has won $1 million from the Ohio Third Frontier Fund, and intends to complete its proof of concept project for large glass substrate panels by the summer of 2012.

Its chief competitor, American company Konarka’s technology, is a photo-reactive polymer material invented by Konarka co-founder and Nobel Prize winner, Dr. Alan Heeger.

This can be printed or coated inexpensively onto flexible substrates, again using roll-to-roll manufacturing.

It can work indoors too, capturing ambient light.

Like Dyesol, Konarka has recently entered a partnership agreement with a steel producer, ThyssenKrupp Steel Europe to develop solar steel roof, facades and other construction elements for building-integrated photovoltaics (BIPV) in Germany.

Dr. Lars Pfeiffer, head of quality and development at the Color/Construction unit. "Unlike conventional silicon-based photovoltaic systems, the joint solar solution will not need to be mounted on a raised structure but will integrate smoothly into the building envelope. We look forward to providing the valuable, added benefits of solar to our customers at a low cost."

Challenges

Some problems remain to be solved. For example, could it survive 25 years?

Rodney Rice says at the moment Tata can produce several square metres, and has installed a 15 m² demonstration roof can be used to test the output and performance.

“We are now developing our abilities in the process, durability, assembly and manufacturing," he said.

It is the dye which is crucial for the generation of the electricity from light. Different dyes are being researched all over the world.

“We are looking for the perfect dye," said Rodney. “The ability to capture light energy from a wide range of wavelengths is required in order to maximise efficiency. More than half research in world is looking at new dyes, extending wavelengths, including into the infrared," he said.

Dyesol is now ramping up more aggressive performance targets under a revised Technology Road Map, to achieve grid parity at an earlier date.

Whichever company is the first to successfully produce cladding for buildings which can cheaply produce electricity, will find themselves at the head of a multibillion dollar market.

Even supposing half of what these companies are claiming is hyperbole, then we are perhaps looking at a ten year timescale rather than five years before the technology reaches mass production.

Even so, this would be before the anticipated timescale for new nuclear power stations to come online. So, the big question is: would it obviate the need for new nuclear power by rendering it uncompetitive?

Thinking about the ease and convenience of producing, installing and using this technology at the point of use, it is clearly going to be a massive game changer.

The missing part of the jigsaw is still electricity storage, since, although this technology can produce energy at night time from indoor lighting, this will not meet peak demands.

This topic will be the subject of another special Low Carbon Kid technology report in 2012.