30 June 2010
The words “solar energy” and “Spanish sunshine” are apparently made for each other. Indeed, the research and development community in Spain has established a high profile in this field over the years, of a standard comparable to world leaders. Manufacturing in the 70s, followed by world-class academic research in succeeding decades, lead to highly successful spin-out companies in the 1990s. This attracted multinational solar companies to Spain.
Today, the Spanish research effort continues with the LIMA (Light Interaction with MAtter) European FP7 project.
The Lima project shows that Spanish research and development continues to benefit from the strong infrastructure developed in the good years...
To put efficiencies in context, work by University of New South Wales in Sydney has lead to silicon textured cells with efficiencies of over 24% reported over a decade ago. This is, in fact, only slightly less than the silicon fundamental efficiency limit of slightly over 25%. And despite this, commercial terrestrial cell efficiencies are typically in the 16% to 17% range under standard test conditions (STC). These are mainly based on omnipresent, abundant and non-toxic silicon. In this context, the relatively low commercial efficiencies achieved are puzzling, being that they are significantly lower than the record. And solar photovoltaic power remains tantalizingly close, and yet more expensive than the canonical 1$/Wp cost often quoted as the economical break-even cost. This suggests that current technologies, as ever, need a fundamental shift to achieve greater efficiencies, and makes new ideas increasingly attractive as time goes by.
In the current economic climate, the Spanish peninsula, despite its important contributions to date, might not seem the most attractive environment do develop new technical solutions. In “Tremors in the Spanish Photovoltaic Industry,” author Esther Perez goes into some detail on the status of photovoltaic research and development. Suffice it to say that the Spanish photovoltaic market has suffered a spectacular reversal in fortunes. And despite this, research and development remains vibrant, an example of which is LIMA. The project shows that Spanish research and development continues to benefit from the strong infrastructure developed in the good years, and puts Spain in a strong position in European research.
The LIMA project has at its heart the concept of improving light interaction with matter. This is because silicon, despite all its advantages, suffers from one weak point: weak absorption coefficient, due to its indirect bandgap. Silicon cells typically have to be made thick as a result. This thickness imposes materials cost, and great material quality constraints, which have to be very low doped and essentially defect free. The LIMA project addresses this from three complementary perspectives: nanostructured active layers, nanostructured plasmonic layers, and resulting novel cell geometries. The initial efficiency aims are nowhere near the world record cells, as the intention is to produce designs that can be commercially viable with currently available production technology. As a result, the maximum efficiency envisaged in the project remains of the order of 20% STC.
Sketch of the LIMA solar cell showing schematically only the plasmonic light scattering mechanism
The genesis of LIMA was the proximity of the Nanotechnology Institute of Valencia (NTC) and solar photovoltaic (PV) system manufacturers in this Mediterranean technological hub. The NTC benefited from links with Spanish photovoltaic industry from its foundation, including technology and personnel transfer from multinational semiconductor interests in Spain. Local Valencian industry subsequently approached the NTC for help in research and development for future product lines. And as a consequence of this dynamic, the solar photovoltaic group of the NTC has seen rapid expansion.
The Nanotechnology Centre of Valencia (NTC)
in the grounds of the Polytechnic University of Valencia (UPV)
LIMA is the first EU photovoltaic project proposed and coordinated by the NTC as a result of this evolving photovoltaic activity and recruitment of research staff. The project was designed first with existing NTC collaborators on nanotechnology projects in optical telecommunications, where existing nanotechnology research interests were seen to have clear applications to the evolving photovoltaic research area.
These prior collaborations include Lorenzo Pavesi’s nanoscience group in the University of Trento (UNITN), which brings expertise on nanostructures generally and quantum dots in particular, including theoretical modelling tasks. Georg Pucker’s group at the neighbouring Bruno Kessler Foundation (FBK) complement UNITN by contributing experience in fabrication of multilayered self assembled nanostructures, including superlattices.
Javier García de Abajo’s group in the CSIC Research Institute brings a world-leading track record in research of theory and applications of plasmonic nanoparticles, in particular as applied to photovoltaic power generation.
LIMA brings a new collaboration, which is Martin Green’s world-leading group at the School of Photovoltaic and Renewable Energy Engineering at UNSW in Australia, which brings a long experience in silicon photovoltaics of the consistently record-holding group world-wide, and also the more recent theoretical expertise on low dimensional photovoltaic designs, and in particular quantum dots. The UNSW group brings expertise on modelling quantum dot structures in high efficiency silicon cell designs, in consultation with FBK, UNITN and NTC.
In parallel, another new partner, the International Solar Energy Research Centre (ISC) of Konstanz, Germany, is bringing expertise in designing high efficiency silicon solar cells for integration with the nano-structures, complementing the NTCs fabrication team developing an alternate solution in parallel.
Finally, Isofotòn of Spain completes the loop with a return to the industrial genesis of the NTC photovoltaic group. They bring an production feasibility, cost and economic viability chapter to the design of final proposed nanostructured silicon solar cell.
To conclude, the LIMA collaboration of seven partners in a European project rooted in Valencia underlines the vibrant research and development atmosphere in this Mediterranean city. The exciting thing about this project is the promise of a first nanostructured solar cell breaking the bond that currently restricts efficiencies to about 17%. The new device physics involved will no doubt hold surprises going beyond the projected efficiencies of around 20%.
Further information is available on the Cordis EU projects site, and on the LIMA consortium website.
About the Author
Dr. James Connolly is photovoltaic senior research scientist at the Nanophotonic Technology Centre of the Polytechnic University of Valencia, responsible for modelling and cell design. He has worked previously on models of quantum well structures for multijunction high efficiency photovoltaics as research fellow at Imperial College London with spin-out company Quantasol UK, and on thin film photovoltaics at the CNRS in France.
Copyright © 2010 Novus Media Today, LLC. All Rights Reserved.