Paul Boughton looks at a project to explore the potential of the ‘wonder material’ graphene in the development of photovoltaic cells.
The vast majority of photovoltaic cells are based on a crystalline silicon construction. These have high power conversion efficiency characteristics, but the drawback is that they are costly to fabricate, requiring use of the highest purity silicon.
Thin film solar cells, in contrast, are relatively inexpensive to make. They have numerous favourable deployment characteristics, but this is counterbalanced by lower power conversion efficiency and shorter operational lifespans than crystalline silicon. But the possibility of carefully engineered incorporation of graphene nanoplatelets (GNPs) within the perovskite charge collecting regions of thin film solid-state dye-sensitised solar cells could boosted efficiency levels.
Through this, the widespread uptake of photovoltaic technology could be accelerated as solar cells that combine cost-effectiveness and high performance would then be brought to market. Increased conversion efficiencies will result in a smaller installed area per unit of generated electricity, reducing the material requirements as well as carbon footprint of the manufacturing process.
Monolayer graphene encapsulation of the entire cell also has the potential to prevent moisture ingress affecting the perovskite layer, increasing the durability of this component in addition to reducing the external toxicity of solar cells based on these materials.
Now 2-DTech, a specialist in the development of graphene solutions, has linked up with solar technology company Dyesol in order to carry out research relating to graphene being integrated into solid-state dye-sensitised solar cells.
2-DTech was formed out the University of Manchester’s pioneering work on graphene and retains the benefits of strong links with this establishment and is based at the university. Now it has been awarded a grant worth £98,000 from InnovateUK to explore the graphene potential. The company is part of Versarien, headquartered in Mitcheldean, Gloucestershire, UK, which produces advanced materials for a range of industry sectors. Partner Dyesol is an Australian clean-tech company developing cutting-edge, clean energy generation solutions. It was established in 2004 to commercialise a third generation photovoltaic nanotechnology called dye solar cells (DSC) or dye sensitised solar cells (DSSC).
Nigel Salter, 2-DTech’s managing director, says: “The UK Government has made a commitment to having 20GigaWatts of installed photovoltaic capacity by 2020. If this is to be achieved there needs to be a major advance in the photovoltaic technology being employed. The key to solar cell design lies in maximising charge collection and graphene could have a major part to play in this. With the financial backing of InnovateUK, 2-DTech will be able to evaluate its merits in this important application area.”
The project to explore this potential will take 12 months to complete.
The potential of graphene is huge. At 200 times stronger than structural steel it is just one atom thick. Its potential has been theorised for years – in composites, energy generation and sensors, for example. However, research and development is all very well – making the ‘wonder material’ a commercial success is vital. And progress has been slow on that front.
Dr Margherita Sepioni is 2-DTech’s research and technology officer. She joined the company in 2012 having completed her PhD in the graphene Condensed Matter Group of Manchester. Her project focused on the magnetic properties of graphene laminates fabricated by chemical exfoliations. Over the past two years, she developed and improved new graphene production methods.
“Currently solid state dye sensitised solar cells cannot perform as well as crystalline cells in terms of their absorption of solar energy or its subsequent translation into electrical energy. Currently thin film solar cells offer power conversion efficiencies which are lower in comparison to crystalline alternatives,” says Dr Sepioni. “Because of its remarkable conductivity and structural properties, graphene could enable a step change in the overall effectiveness of thin film solar cell technology – improving both the conversion efficiency and the cell durability. This would mean that the industry could be provided with photovoltaic devices delivering higher performance at a competitive point.”
But it will not be plain sailing to achieve this. “There is quite a lot of research going on in graphene for photovoltaic applications and integration of graphene inside solar cells,” Dr Sepioni says, “but there are a few problems. First of all the fact that costs to produce graphene are still high and, I would say from a technical point of view, the concern is the efficiency of the solar cells. They still can’t compete with the current ones (crystalline silicon construction). So that is a big question.”
The project, says Dr Sepioni, will explore different sources of grapheme and different kinds of deposition inside the solar cell. “I would say we have quite a strong plan and we hope it is going to work.”
Solar cell energy conversion efficiencies for commercially available cells are around 20%, says Dr Sepioni. “It would be really optimistic to achieve that number because 20% is really what the current state-of-the-art is, but we are aiming to approach that number.”
Graphene has been the most studied material since 2004, she says and “every day we find new published works saying we have found a new effect and graphene can be used for this and can be used for that. But there is a huge gap between the basic research and the commercialisation aspects. So we still cannot really buy any graphene-based products, although I have to say that some competitors have started commercialising some products.”
She continues: “The other thing is graphene is really good as a conductor and as a transparent layer so there were a lot of expectations in terms of replacing silicon technology and also just having a big role in technology in general. But, again, the costs in producing these small samples are huge. Probably I see more promise in what graphene will do in other fields like composites, batteries, replacing amorphous carbon, carbon fibre in structural projects more than in electronic devices.”
The Commercial Graphene Show Europe 2015
Every industry must start somewhere, and every industry needs to be pushed forward. And that is where The Commercial Graphene Show Europe 2015, which will take place at Manchester Central Convention Complex, UK, between the 16th-17th April 2015, comes in.
The graphene industry’s challenge lies with scaling up production and gaining pace in the mainstream market, say organisers Terrapin. R&D catches up with production, networking creates collaboration and breakthroughs lead to commercialisation.
The show will cover all aspects of grapheme’s potential – aerospace and defence, energy storage and batteries, electronics, printing and packaging, automotive, paints, coatings and barrier applications
“This is the perfect opportunity for the entire graphene value chain to come together. There’s no event like it, and that’s what makes it unmissable.
“This is the place where collaborations for industrial applications will be initiated and influenced, and the future of graphene will be strengthened.
“Join us for this once-a-year experience, and come away with answers for the sceptics and new relationships with those who are serious about business. Use The Commercial Graphene Show as your opportunity to take the graphene industry to the next level,” say the organisers.
For more information, download the brochure now at www.terrapinn.com/commercial-graphene
