Introduction
Photovoltaic
Current scientific status
Current technological developments
Developments of silicon photovoltaic markets and technology
Hybrid organic/inorganic solar cells
Solid state organic solar cells
Needs for breakthroughs
Scalability of semiconductor materials
Decreasing the energy payback time of solar cells
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Reducing the energy input in photovoltaic modules production. Low-temperature processes, substrates with low embodied energy, repeated use of substrates for growth of high quality materials/devices, closure of the materials cycle during the life cycle of devices;
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Extending the technical lifetime of high performance photovoltaic by improved encapsulation and protection.
Materials design
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Designing the electronic properties of carbon-based materials by understanding and controlling the path from single molecular structures via nano-morphology to film growth. A prime example is bulk heterojunctions in organic solid state solar cells which need a nanometer control of morphology in the key active layer.
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Multiple-band gap tandem solar cells incorporating scalable materials;
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Light concentration through far field optics for multiple-band gap materials;
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Nanophotonics in dielectrics and semiconductors for light-matter coupling, light trapping/ light management;
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Plasmonics for light-matter coupling, to direct energy to the semiconductor structure in photovoltaic devices;
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Combination with solar fuel generation, e.g., hydrogen generation by photovoltaic layers with catalyst electrodes.
Identification of research needs of the coming decades
Nanophotonic strategies for light trapping in thin structures
Transparent electrode materials, not relying on elements of low abundance
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Carbon based or abundant metal oxide transparent conductors for electrodes;
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New combinations of device/module assembly to generate lower currents and higher voltages for decrease of losses in photovoltaic modules.
Beyond S–Q limits?
Solar fuels: Artificial photosynthesis
Predicted power conversion efficiencies: Direct processes for solar fuel
Methods to produce direct solar fuels
Direct solar fuel needs for breakthroughs
Efficient photo-sensitizers and photocatalysts
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Photo-sensitizers frequently contain noble metals (ruthenium), which have to be replaced with cheap and abundant elements. Iron is one example but dyes based on Fe and similar transition metals have unfavorable properties for solar energy conversion, necessitating scientific breakthroughs. At the same time fully organic dyes are appearing. Thus, it can be expected that sensitizers suitable for most applications and for large-scale implementation are likely to appear in not too distant future.
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To achieve highly efficient catalysts for water oxidation and hydrogen (liquid fuel) generation is a considerably more difficult and complex problem. Catalysts may be either molecular complex or solid state (e.g., metal oxide) based. Understanding the mechanisms of O-O and H-H bond formation is key to the development of efficient catalysts. Most of today’s catalysts have low efficiencies and are frequently based on scarce or noble metals, making them unsuitable for large-scale commercial implementation. Here, scientific breakthroughs are needed, both concerning efficiency and developing new catalysts based on abundant and cheap elements. Proof-of-concept catalysts with high efficiencies, based on metals like ruthenium, are likely to appear within the next 10 years, but catalysts suitable for commercial applications most likely will take considerably more time.