HETSI

Heterojunction Solar Cells based on a-Si c-Si

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 Obiettivo del progetto (Objective)

'The Photovoltaic (PV) industry needs to find new approaches to make solar cells competitive. Crystalline silicon (c-Si) wafer-based technology has a real potential to achieve significant cost reduction if the R&D effort is made on the most critical issues. These issues are the reduction of silicon material consumption, the increase of solar cell efficiency and an improved integration into modules. In this context, silicon heterojunction solar cells, the active part of which is basically produced by a low temperature growth of ultra-thin layers of silicon onto both sides of a thin crystalline silicon wafer-base, represent clearly one of the most promising options. The HETSI project aims to design, develop and test novel aSi-cSi Heterojunction solar cell structure concepts with high efficiency. This project covers all aspects of the value chain, from upstream research of layer growth and deposition, to module process and cell interconnection, down to upscaling and cost assessment of heterojunction concept. The Consortium is a balanced team of 12 partners from 6 European countries with a wide range of expertise in the field of silicon for PV covering various aspects from the deposition of thin silicon films, passivation of interfaces, through characterization and modelling, down to technological implementation and industrial achievement capabilities. The cooperation of Europe’s leading research institutes in the field of heterojunction solar cells (HMI, ECN, CEA-INES, IMEC, UNINE, UU, ENEA and CNRS) will generate synergy effects that will help to provide the know-how needed to reach the optimum relation of cell efficiency and cost. The presence in the consortium of 3 industrial partners, Q-Cells, Photowatt and Solon, which are among the leading European solar cell and module producers, will insure a rapid and efficient economic exploitation of HETSI results.'

Introduzione (Teaser)

Cheap and efficient solar cells can make an important contribution to combating climate change. Europe's leading research institutes in the field of heterojunction solar cells are joining forces through the HETSI project to investigate new ways of making solar cells even more competitive.

Descrizione progetto (Article)

Crystalline silicon (c-Si) wafer-based technology has genuine potential for significantly reducing the cost of solar cells. However, a number of critical issues must first be addressed. They include a reduction in the amount of silicon material consumed (for example using thinner wafers) and an increase in solar cell efficiency.

One of the most promising avenues of research is silicon heterojunction cells, which depends on a low temperature growth of ultra-thin silicon layers on both sides of a crystalline silicon wafer substrate. The role of the EU-funded HETSI project is to design, develop and test more efficient heterojunction solar cells that are compatible with high-throughput mass production. The cell design is based on an emitter and back surface field produced by a low temperature growth of ultra-thin layers of silicon.

Modelling new concepts is crucial to effective design and development. Simulation results obtained with two different softwares have shown excellent correlation. The software has now been upgraded to take into account additional factors. Project partners have also developed wet-chemical processes and dry cleaning processes that have resulted in higher cell efficiencies.

Different deposition methods for doped metal oxides used in photovoltaics, called transparent conductive oxides (TCO) and include indium tin oxide (ITO), have been compared. The sensitivity of ITO in damp heat tests on solar cells shows that aluminium foil is required on the back to prevent the penetration of water. Metallisation conducted with low-temperature screen printed pastes from a number of different suppliers reveals that resistivity is too high for a single print process and a multiple print process should be investigated. Metallisation was finally applied to actual large area solar cells.

The HETSI project shows that a new approach can be applied to the development of a competitive solar cell using c-Si wafer-based technology to reduce costs and increase efficiency. The results will also help boost the European solar cell industry and create more jobs in the renewable energy sector of the new green economy.