Emerging off-grid power markets in Africa and Asia are being targeted by UK solar technology start-up Eight19 for the roll-out of an innovative “printed” organic PV (OPV) film it will start producing early next year.
Spun out of a pioneering optoelectronics group in Cambridge University’s physics department, Eight19 has taken up the torch to commercialise an environmentally friendly, low-cost, flexible plastic solar cell suited to high-volume, low-power applications such as solar lamps, chargers for mobile phones or laptops and portable greenpower generators.
“These are the markets we are after. Some call them niche markets but, as niches go, they are pretty big: the lighting market in Africa is worth $38bn, while mobile chargers in India alone represent a market of $5bn-15bn,” states recently appointed chief executive Simon Bransfield-Garth. “These markets suit very well the characteristics of the plastic solar cells.”
The company sees its OPV technology — which last year received a £4.5m ($7.35m) shot in the arm from the UK’s Carbon Trust and international specialty chemicals company Rhodia — as having great potential to bridge the widening energy gap in developing countries with a renewable alternative to local diesel generation.
“The peak-energy gap in India, for example, is set to grow [from current levels of about 12%], as average electricity consumption doubles over the next five years,” says Bransfield-Garth. “As with a number of emerging economies, the high cost of energy and limited infrastructure is spurring a dramatic rise in off-grid renewables.
“Our plastic solar cells can help replace fossil fuels with clean, cheap, renewable energy that will stimulate education, commerce and the pace of development, where they are deployed.”
There is a lot to like about Eight19’s OPV technology. Organic polymers and “small molecules” — low-molecular-weight organic compounds that are also carbon-based but not classified as polymers — are simple and inexpensive to synthesise in the lab and use none of the exotic — and sometimes highly toxic — substances seen in conventional crystalline silicon (c-Si) PV.
“Standard organic chemistry methods” that can vary the make-up of the PV materials are employed in synthesis to hone performance of the film’s PV materials, which are applied from solution at room temperature onto low-cost flexible substrates. This way, OPV can be “printed” roll-to-roll on continuous webs, making the concept easily scaleable off the back of a small boost in capital outlay.
The final product is a “mechanically robust”, flexible PV film with a thickness “in the tens of nanometres” that will suit applications in locations lacking basic solar-power infrastructure, says Bransfield-Garth.
“The price of a [CSi] solar cell is coming down to the point where the balance-of-system cost [which includes the cost of housing and mounting the PV panel] is becoming more and more important,” he states. “If you are trying to make a five-watt [W] solar module, you are probably spending more on the frame, the cabling, the front glass and so on than you are on the solar cell.
“With a plastic solar cell, you don’t need any of the housing and the rest, so you are competing with conventional PV less on the bulk cost of solar cells and more on the system level, and here plastic solar cells are very cost effective.”
Although Eight19 admits to being “at the early stages of the volume production learning curve”, the company has set a target of manufacturing OPV modules with a $0.50/W sticker price. With the high-speed, continuous roll-to-roll technology available, production rates of one metre per second are achievable, which, on a one-metre-wide web, would translate into fabrication of 3.6km of the film each hour.
“What you tend to find today, is someone making, say, a 5W amorphous silicon solar cell with a cell cost in the order of $1, for the sake of round numbers. In a small solar cell, the cost is probably twice that because the total system cost is much bigger,” notes Bransfield-Garth.
“It is incorrect to compare bulk costs when you are looking at OPV versus conventional c-Si; it is the ‘in application’ cost where the comparison really works.
“Volume is the thing. Our manufacturing line will be avoiding high-temperature processing and vacuum processing, so the throughput of the technology is potentially very high. Also, the capital cost of the manufacturing equipment would be considerably lower than using conventional [production] technologies, a fraction of the ‘one watt of capacity per dollar’ rule of thumb generally used.”
The manufacturing facility being built behind Eight19’s Cambridge headquarters will start as a “development line” but, as it will use a printing process, will have the capacity to produce hundreds of thousands of modules per year to meet the company’s early-stage manufacturing needs.
OPV can have light absorption rates 100 times greater than c-Si, but, historically, it has been stymied commercially by its poor conversion efficiencies. Recent years have seen percentages increasing, however, with “champion” OPV cells having demonstrated efficiencies as great as 8%. Finished OPV modules are seeing efficiencies of 4-5%, a figure Bransfield-Garth reckons will be incrementally improved through “tuning” the chemical composition and interfaces of the cell.
Another key issue is operating lifetime, as OPV degrades quickly. Eight19 has carried out accelerated-lifetime tests on its film with a view to extending its operational use to up to five years.
“It is a cost/lifetime trade-off. For many of the markets we are looking at, the customers would rather have a low-cost product with a modest lifetime than a high-cost product with a very long lifetime,” remarks Bransfield-Garth.
“It is an ongoing development and there are reasons to be optimistic. If you look at the electronic display industry, they have gone from displays that lasted just hours to displays that last virtually for ever. There are reasons for hope that the same will happen in the OPV industry.
“This is just one among the 40 or 50 difficult technical problems that need to be solved to optimise the solar cell, particularly in terms of cost per watt and operational lifetime.
“There is plenty to keep us occupied, both in terms of lifetime optimisation and performance optimisation. For instance, you need to eliminate ITO [indium tin oxide] as the transparent conducting electrode; you have to come up with the best interface layers that optimise the electron and hole transport [which creates the electrical charge] inside the materials; you’ve got to find the right way of encapsulating the device to ensure a long lifetime in real-world circumstances, and so on.
“It is not so much a ‘secret sauce’ as it is a secret recipe as to how you get from raw materials to finished product — and that is partly down to the design of the modules and partly down to the process steps you take to ensure you have reliable, high-yield manufacturing.”
Taking personal and community off-grid generation technology as its starting point, Eight19 predicts its campaigns in emerging power markets in Africa and Asia will be “industrial scale” in their potential scope.
“There are two ways you can go with this technology. You can try to take OPV into established PV markets or you can build whole new markets in their own right,” offers Bransfield-Garth. “Our view of this is that the small-scale, off-grid markets together represent a very substantial opportunity. It is a matter of building out the markets where we see OPV being particularly valuable.”
