For the electronic cells to be viable on an industrial scale, they would have to be made through roll-to-roll processing. The encapsulation of a flexible cell also poses a major challenge. If encapsulation is insufficient, liquid electrolyte could leak out of the cell or impurities could seep in, considerably reducing the lifetime of the device.
'Flexible solar cells are usually made on metals or plastics, and both come with perils: a metal may corrode, and plastics may allow water and other impurities to permeate," said Dr. Kati Miettunen, a project manager at Aalto's Department of Bioproducts and Biosystems.
New innovations will also be needed to join the substrates together, since conventional techniques such as glass-frit bonding now used in flat-panel displays and other devices, are unsuitable for flexible cells, say the researchers.
"Another prerequisite for commercialization is making the lifetime of devices adequate in relation to the energy that is embedded in the fabrication of the decices, so that the solar cells won't degrade before they have produced more energy than was used for making them," said Jaana Vapaavuori, now assistant professor of the chemistry department of Université de Montréal.
New discoveries using biomaterials, or a hybrid material with wood pulp as substrates for the cells, could pave the way forward, said Miettunen, who is working with UdeM's department of chemistry in her research. These materials' natural ability to filter out impurities would work well for solar cells. The prototype develoed by the team uses a photoanode of a dyed nanoporous TiO 2 layer on a conducting substrate. The counter electrode is a conductive substrate coated with a catalyst layer. The space between the electrodes is conventionally filled with liquid electrolyte.
German company Heliatek is already producing dye-based solar cells on a flexible film substrate using a roll-to-roll process and is moving to large scale production.