GO-NEXTS

Graphene doping and texturing in efficient electrodes for organic solar cells

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 Obiettivo del progetto (Objective)

'Organic semiconductor solar cells are a promising route to scalable, economically viable, energy conversion technologies due to the potential for development of low-cost, flexible, large-area cells and modules. In order to achieve the goal of obtaining efficient bulk heterojunction solar cells (BHJ-SCs), graphene electrodes have been recently proposed as a promising candidate. Research is however at the very beginning, so that if graphene will manage to accomplish this task still has to be proved. In particular, many questions remains open like the degree of interaction of graphene with the polymeric layer, which could degrade the outstanding graphene electron conductivity, as well as the graphene/polymer electron affinity, which plays an important role in the overalls solar cell efficiency. Furthermore, up to now no analysis on light management improvements induced by structuring graphene as photonic crystal for light trapping in BHJ-SC has been reported. The GO-NEXTS project, will focus its attention on new kind of electrodes based on doped, textured (ie 3D) graphene electrodes, in order to increase the overall efficiency and performance of bulk heterojunction solar cells. To our knowledge, this represents the first proposal to enhance light trapping in a solar cell by structuring one or more graphene contact electrode(s) to act as photonic crystal(s). The project will leverage the combination of two different fabrication processes, and in particular the doping of the graphene, to obtain semi-transparent electrodes as well as the texturing of the electrodes. This approach, which has never been proposed before, represents a high-risk, high-impact approach. If successful, it should lead to improvements in solar cell efficiency by up to 14%. Furthermore, all the technologies proposed are suitable for large area realization paving the way for a scalable, economic fabrication technologies on low-cost flexible substrates.'

Introduzione (Teaser)

More energy from sunlight strikes the Earth in one hour than all the energy consumed by the planet in one year. Organic solar cell technology exploiting graphene could make harvesting this bounty both efficient and cost effective.

Descrizione progetto (Article)

The first and second generation of solar cells are based largely on silicon. Organic (polymeric) solar cells promise important benefits. These include flexibility and reductions in costs for large-area surfaces thanks to well-established polymer processing routes.

Graphene electrodes with their excellent conductivity have recently been identified as a promising candidate to achieve efficient bulk heterojunction (BHJ) solar cells proposed more than 25 years ago. However, the mechanisms and effects of integration with a polymeric thin film remain to be determined. The EU-funded project 'Graphene doping and texturing in efficient electrodes for organic solar cells' (http://www.go-nexts.eu/ (GO-NEXTS)) plans to structure one or more graphene contact electrodes to act as photonic crystals.

Photonic crystals are periodic dielectric structures with a bandgap forbidding propagation of certain wavelengths of light. They can be likened to the energy bandgap between valence and conduction electrons of semiconductors. This enables exquisite control over electromagnetic radiation not possible with conventional optics. It should facilitate unprecedented enhancements in overall efficiency and performance of BHJ solar cells. During the first year and a half, researchers focused on the simulation and fabrication of individual components.

In particular, scientists studied the role of graphene-metal contacts, and modelled the graphene electronic properties and the grated contact optical properties. Together with evaluations of effects of various design parameters such as layer thickness, results have pointed the way to promising fabrication activities.

Partners studied chemical vapour deposition (CVD) processes for graphene onto various substrates and graphene growth onto textured photonic crystal substrates. Low-temperature CVD was not able to produce graphene of high enough quality for photovoltaic applications. In contrast, the graphene growth process is now close to state-of-the-art.

The second period will focus on optimisation of growth on planar substrates and of doping protocols. Parallel work on fabrication of organic BHJ solar cells has led to performance equivalent to that of current state-of-the-art BHJ solar cells.

GO-NEXTS is progressing towards delivery of transparent electrode materials, fabrication processes and device architectures. Implemented in BHJ solar cells, they will lead to low-cost and high-efficiency organic photovoltaics.