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Solar Energy Materials

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

A schematic representation of a perovskite-based solar cell that we are developing along with partners in the EU FP7 project PLIANT
A schematic representation of a perovskite-based solar cell that we are developing along with partners in the EU FP7 project PLIANT- Process Line Integration for Applied Surface Nanotechnologies and the EU H2020 project CHEOPS –  Production technology to achieve low Cost and Highly Efficient photovoltaic Perovskite Solar cells. In the figure the term ETL refers to an electron transport layer, while the terms HTL refers to a hole transport layer.

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.

A cross-sectional transmission electron microscope image taken from one of the active layer stacks grown at Tyndall
A cross-sectional transmission electron microscope image taken from one of the active layer stacks grown at Tyndall. This stack forms the basic structure of a real perovskite-based photovoltaic device.This image may be compared with the schematic image above.

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).

A schematic representation (left) and a TEM image (right) of a photoelectrochemical water splitting device fabricated using CMOS technology which utilizes atomic layer deposition to grow protection layers designed to overcome issues with the photocorrosion of the anode material, in this case silicon
A schematic representation (left) and a TEM image (right) of a photoelectrochemical water splitting device fabricated using CMOS technology which utilizes atomic layer deposition to grow protection layers designed to overcome issues with the photocorrosion of the anode material, in this case silicon. This image is taken from the Nature Materials 2011 paper from our collaborators on the RENEW project, the group of Prof Paul McIntyre at Stanford University California.

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.

A scanning electron microscope image of a ‘field’ of ZnO nanorods
A scanning electron microscope image of a ‘field’ of ZnO nanorods grown at Tyndall by PhD student Mr Jan Kegel using a combination of atomic layer deposition (ALD) to grow a seed layer followed by hydrothermal growth from a zinc acetate solution. The resulting nanostructured ZnO layer is both highly absorbing towards soft uv radiation and also highly luminescent. Materials such as this are being prepared at Tyndall as potential photoanode structures for the splitting of water into hydrogen and oxygen supported by the US: Ireland project RENEW- ‘research into nanostructured electrodes for the splitting of water’, which is collaboration between Tyndall, Queen’s University Belfast (Prof Andrew Mills) and Stanford University (Prof Paul McIntyre).

 

 

 

 

 

 

 

 

 

 

A schematic representation of how a colloidal photonic crystal thin film may be used in so-called building integrated photovoltaics
A schematic representation of how a colloidal photonic crystal thin film may be used in so-called building integrated photovoltaics. The photonic crystal film is attached to the window glass and acts as a light trap such that some of the light that falls upon the window suffers internal reflection within the pane of glass and as a consequence is directed towards the window frame, where the solar cells are located. Thus the windows in the house act as passive sources of solar energy. This image is taken from ‘Gudrun Kocher-Oberlehner et al., Solar Energy Materials and Solar Cells, 104, (2012) 53-57’.

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.

Transmission electron microscope image of a thin (40 nm) layer of ZnO grown on glass using atomic layer deposition (ALD) at Tyndall
As an example of a transparent conducting oxide (TCO) or more generally a transparent conducting material (TCM) which finds application in a variety of photovoltaic devices, the image above depicts a transmission electron microscope image of a thin (40 nm) layer of ZnO grown on glass using atomic layer deposition (ALD) at Tyndall. Using a nanolaminate approach to doping with ions such as Al3+ we have already achieved thin film resistivities of better than 2× 10-3 ohm.cm.

 

 

 


 

 

 

 

 

 

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.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A photograph of some microscope-sized pieces of glass coated with V2O5- a naturally layered electrochromic material using an atomic layer deposition (ALD) process
A photograph of some microscope-sized pieces of glass coated with V2O5- a naturally layered electrochromic material using an atomic layer deposition (ALD) process developed at Tyndall by PhD student Mr Igor Kazadojev and Dr Ian Povey.Materials such as these change colours dramatically when Li+ ions are electrochemically inserted into the structure and so have application in a range of colour change devices and smart window technologies.

 

Left: A photograph of the roll-to-roll doctor blade/ slot die coating system at Tyndall which was provided by our collaborators in Brazil, the group led by  Prof Roberto Faria. This system has been used to create a range of flexible organic light emitting diodes (OLEDs) and organic photovoltaic devices (OPVs). Right: an example of one of the OLED devices made at Tyndall by Dr Mikhail Parchine using our roll-to-roll system
Left: A photograph of the roll-to-roll doctor blade/ slot die coating system at Tyndall which was provided by our collaborators in Brazil, the group led by Prof Roberto Faria. This system has been used to create a range of flexible organic light emitting diodes (OLEDs) and organic photovoltaic devices (OPVs). Right: an example of one of the OLED devices made at Tyndall by Dr Mikhail Parchine using our roll-to-roll system.

 

 

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