An engineer at TU Delft has developed a process to produce inexpensive solar cells 10 times faster than existing systems without any detriment to their energy yield.
It is claimed that this will almost certainly result in a further reduction in the price of the cells, which are made of amorphous silicon.
The cost of electricity generated using solar cells is still costly, partly owing to the characteristics of the most widely used material in solar cells — crystalline silicon.
’An interesting alternative to crystalline silicon is amorphous silicon,’ said Prof Miro Zeman of TU Delft. ’Although this material has a lower energy yield than crystalline silicon, solar cells based on it can be produced far more cheaply. The nature of the material means that much thinner layers can be used — around 250nm thick, compared with the 200μm-thick layers of crystalline silicon.’
Amorphous silicon solar cells are already being produced for this reason. ’But one significant problem for the industry is that the usual technique used to produce the cells — which involves vaporising silane gas to deposit the amorphous silicon on glass — is too slow,’ said Zeman. ’It takes about one second to apply a 0.1nm layer, so to apply a complete 250nm layer requires about 40 minutes.’
To speed up that process, PhD student Michael Wank turned to a newer expanding thermal plasma chemical vapour deposition (ETP-CVD) production technique, which he demonstrated could speed up the production by a factor of 10 — to 1nm per second — while maintaining a yield of around seven per cent.
But a conventional ETP-CVD production technique could not be used owing to the fact that it requires a temperature of around 350oC — a temperature that would cause damage to the solar cells and affect their energy yield. To circumvent this, Wank applied ion bombardment during the production process, which enabled the production to take place at a much lower temperature of around 200oC.
’The results of the research are of great interest to industry, which can use the method to make solar cells quickly and inexpensively,’ said Zeman. ’As well as the greater speed, another benefit is that the machines needed for this technology are smaller. All in all, this technique promises to cut the production costs of this type of solar cell considerably.’
Wank’s PhD project, which was subsided by Agentschap NL, was carried out in collaboration with the Plasma and Material Processing group of Prof Richard van de Sanden.