The answer to the question posed above isn't clear. I went to a session about plastic devices that could be used as solar cells instead of expensive silicon, hoping to hear a breathrough was nigh. Sadly i was wrong. Advances in plastics that can capture light over a useful wavelength, that can separate the charge into electrons and holes, that can carry that charge and finally, do something useful with it are being made. But slowly.
Talking in the session was Fred Wudl, who was first to develop fullerene/polymer systems as photovoltaic cells. It seems that the system he hit upon first up has been hard to beat, at least according to Mats Andersson, from Chalmers University of Technology, Gothenburg, who was also speaking in the session.
Percentage power conversion efficiencies remain low. The very best results are around 5%, and these tend to be from a single, meticulously prepared sample - a long way from a manfacturable, large scale printing porcess that is hoped for. To be really viable, a system that is 10% efficient is needed, or a slightly less efficient, but very cheap plastic material that can be made to cover a large area. But still, despite lots of tinkering with the polymers in the systems, the best that Andersson presented was 2.8% efficiency. Manpreet Kaur, from Virginia polytechnic presented a system with an efficiency of 1%.
The systems rely on the electron-transporting porperties of a polymer, and the hole (absence of electron) transporting properties of the fullerene groups. The main way to change these systems is altering the polymer groups.
The field is gaining strength, however. One company, Konarka, is claiming that it will have a flexible, efficient, solar cell plastic available by the end of the year. We shall have to wait and see.
The session certainly generated interest, but i can't help think that the efficiencies are going to remain low for a while yet. Perhaps next year, if Konarka has delivered, academics will have joined them in finding a more efficient system.