RESEARCHSPOTLIGHT
The Centre’s work on thin film photovoltaics is primarily based on thin film CdTe and CIGS. In both cases, the work is focused on devising new processes for lowering the cost of PV modules either by improving efficiency or by devising processes that are automated, continuous and which make most efficient use of materials.
A large scale magnetron sputtering tool is being used to devise new processes for each of the layers in the thin film CdTe stack. Sputtering produces thin films with uniformity in the +/- 1% range which is far superior to the conventional close space sublimation technique. This allows the absorber thickness to be optimised which also has implications for downstream module production processes. CREST is working with a number of industrial partners on improving cell efficiency, building integrated products and novel interconnect processes. The equipment used is capable of producing 300 x 100mm mini-modules, but the processes developed are scaleable to industrial scale in-line production tools.
The Centre has a number of other deposition tools and another area of focus has been the development of improved or lower cost transmitting conducting oxides (TCO’s). One outcome of this work has been the development of processes that lead to the deposition of super- smooth ITO. Smoothness of the TCO is important since the CdS buffer layer is very thin and roughness in the TCO can cause shunting.
Cell and Module performance CREST is particularly strong in measuring cell and module performance and has a long history of working with and providing services to the solar industry. The Centre has a large group working on understanding the risks associated with installing modules and systems. Their work has shown that the main risk involved in any PV installation is in the energy yield of systems. This tends to be dominated by system up-time and the initial rating of the modules, which are both key areas of research. Failure mode analysis of fully encapsulated modules using innovative techniques such as luminescence measurements or laser- beam induced current measurements are helping to develop a better understanding of these risks.
Work ranges from physical modelling of device structures to evaluate if certain structures have a benefit in the energy yield over competing
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approaches through to quality assurance of large scale systems. An emphasis is placed on understanding and modelling module performance. This involves power rating using a large area solar simulator, durability investigations as well as energy yield estimations. These measurements underpin the development of models for the long-term energy yield of modules using all technologies. CREST is active in investigating the idiosyncrasies of new and emerging device technologies and investigating the homogeneity of large area modules.
The characterisation of modules and systems often reveals the limitations of commercially available equipment and another focus is the development of the equipment required for high performance characterisation. As an example, CREST has developed a high performance Class A LED based solar simulator.
Concentrators and Solar thermal In parallel with the work on c-Si devices specifically designed for CPV, another team is looking at the optical design, thermal management and performance of concentrator PV systems with concentrations ranging from 2.4x to 300x. Building integrated PV façade systems have been designed
Researcher measures the response of a BIPV module in
Loughborough’s Solar Simulator.
www.solar-pv-management.com Issue V 2010
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