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Carbon-based photovoltaics

Harnessing the Sun's virtually unlimited energy to produce electricity with photovoltaics (PVs) is a promising sustainable alternative to the combustion of fossil fuels. Novel insight into organic semiconductors could provide the needed breakthrough.
Carbon-based photovoltaics
Technology has progressed tremendously within the last few decades and numerous systems are in place around the world. Conventional PV technology, primarily based on silicon, is now in its third generation employing inorganic thin-film PVs. However, widespread implementation has been inhibited by challenges associated with manufacturing costs and conversion efficiency.

Solar cells employing organic semiconductors such as polymers with carbon backbones are easily processed at low costs. Heterojunction structures in which electron donor and acceptor semiconductor layers are mixed can facilitate electron movement, thus increasing efficiency. Scientists focused on two potential systems with EU funding of the project 'Spectroscopic insight with nanoscale resolution on model photovoltaic systems' (NANOPV).

The first was covalently linked organic heterostructures consisting of well-separated entities of differing electronic properties. The team sought out routes for covalent coupling of precursors that would lead to formation of graphene nanoribbons (GNRs). Graphene is a nano-structured form of carbon, a one-atom–thick sheet of carbon atoms.

Using two different chemical synthesis methods on a variety of substrates, the team successfully produced atomically precise GNRs wider than those previously reported. This led to associated smaller band gaps (the smaller the band gap, the more conductive a material is). In addition, the chemical changes observed were different and more complex than those anticipated.

The experiments provided unprecedented insight thanks to the visualisation of covalent bond rearrangements during GNR formation. The associated manuscript has been accepted for publication in the highly esteemed peer-reviewed journal Science. Several other articles are in various stages of review or publication in other prestigious journals.

Scientists also synthesised and characterised a large number of non-covalently linked bi-component molecular blends. Aside from increased understanding of specific deviations in certain systems, the team uncovered an important trend regarding stoichiometry-dependent interfacial energy alignments in donor–acceptor blends on metal surfaces. Forthcoming publications highlight the important results.

NANOPV results are expected to have important impact on the development of organic PVs with potential cost reductions and increases in energy conversion efficiency. In fact, enhancing electron movement will have important impact on organic-based electronic devices for numerous additional applications as well.

Related information

Keywords

Photovoltaics, organic semiconductors, heterojunction structures, graphene nanoribbon
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