Advanced Thin Film Materials and Devices for Solar Energy Applications:
Transparent Conducting Oxides, Photoelectrochemical Water Splitting, Flexible Organic LEDs (OLEDs), Flexible Photovoltaics (OPVs) and Colloidal Photonic Crystal Light Trapping Media
The Advanced Materials and Surfaces group at Tyndall is very active in the development of a range of materials and devices for use in the production of solar energy.
These materials range from transparent conducting materials (usually but not always oxides) which act as the electrodes that permit sunlight to enter the solar cell while also providing an anti-reflective coating that doubles as an electrical contact, to novel materials and devices based on silicon nanoparticles incorporated into ZnO matrices or the perovskite mixed inorganic/organic compounds that have emerged in recent years as highly promising, cheap alternatives to conventional silicon based photovoltaic materials.
In addition the group studies materials and complete device structures for the production of clean fuels such as hydrogen via the photoelectrochemical splitting of water, flexible, light-weight solar cells and light emitting diodes made from cheap recyclable materials such as organic polymers and layered materials such as V2O5 and VO2 which may find application in lithium ion battery technologies or electrochromic devices (V2O5) and potential thermochromic devices (VO2).
So-called ‘smart windows’ based on electrochromic or thermochromic materials such as these can be used to reduce the energy footprint of buildings through the optical control of IR absorption and reflection.
Finally, the group utilizes colloidal photonic crystal light trapping anti-reflection layers that can help to improve device efficiencies. A particular feature of the work at Tyndall concerns the drive to prepare these materials and devices using industry compatible methods, including atomic layer deposition(ALD), chemical vapour deposition (CVD) and roll-to-roll processing.
ZnO is also useful for photovoltaic applications in the sense that it can not only form TCO layers similar to those shown in the previous example, but it can also act as a host medium for other, somewhat unconventional absorber films such as those made from preformed silicon nanoparticles. The image on the left shows such particles made using wet chemical means and then deposited in a matrix of ZnO using chemical vapour deposition (CVD) methods. On the right the external quantum efficiency of a silicon nanoparticle device (also shown schematically) is plotted as a function of the wavelength of the incident light. The variation in the size of the silicon nanoparticles gives rise to quantum confinement effects which result in the creation of an absorbing medium which can respond to light over very wide spectral range. Taken from Perraud et al., Physica Status Solidi A (2012), this work represents an international collaboration with CEA LITEN, University of Toulouse, University of Delft, University of Uppsala, CNRS Toulouse and SAFC Hitech UK.
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