Making say an OLED or organic photovoltaic device require conductors, usually calcium, magnesium or lithium, that have a low-work function. However, these metals are chemically very reactive, and oxidise and stop working if exposed to oxygen and moisture. To overcome this organic photovotlaics must be encapsulated either via another sheet of glass or by a thin-film encapsulation technique. Both of these approaches increases material costs, and makes it more difficult to produce truly flexible devices.
However, a research team from the Center for Organic Photonics and Electronics (COPE) at Georgia Tech have recently published in the journal Science what the researchers believe could be a universal technique for reducing the work function of a conductor. This would reduce the need for using reactive metals for electrodes.
The approach involves spreading a very thin layer of a polymer, approximately one to 10 nm thick, on the conductor’s surface to create a strong surface dipole. The interaction turns air-stable conductors into efficient, low-work function electrodes.
The commercially available polymers can be easily processed from dilute solutions in solvents such as water and methoxyethanol.
To illustrate the new method, the research team evaluated the polymers’ performance in organic thin-film transistors and OLED devices. In addition, the team build what they claims is the first “completely plastic” photovoltaic.
Bernard Kippelen, director of Georgia Tech’s Center for Organic Photonics and Electronics (COPE), said, “These polymers are inexpensive, environmentally friendly and compatible with existent roll-to-roll mass production techniques.” Bernard added, “Replacing the reactive metals with stable conductors, including conducting polymers, completely changes the requirements of how electronics are manufactured and protected. Their use can pave the way for lower cost and more flexible devices.”
Seth Marder, associate director of COPE and professor in the School of Chemistry and Biochemistry, said, “The polymer modifier reduces the work function in a wide range of conductors, including silver, gold and aluminium.” Seth added, “The process is also effective in transparent metal-oxides and graphene.”
Science 20 April 2012: Vol. 336 no. 6079 pp. 327-332, DOI: 10.1126/science.1218829 – “A Universal Method to Produce Low–Work Function Electrodes for Organic Electronics”
The research was funded in part through the Center for Interface Science: Solar Electric Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001084, by the STC Program MDITR of the National Science Foundation under Agreement No. DMR-0120967, and by the Office of Naval Research (Grant No. N00014-04-1-0120).