The ability to print them by the same processes and on the same foil as an array of polymer solar cells opens up the possibility of, e.g. intelligent windows operating without the need for batteries or external power.
Electrochromic materials can change their transparency when an external voltage is applied. Such materials have interesting applications in windows. Thus, one can imagine a window in an office or a greenhouse which automatically pulls the shade by making itself darker, when the temperature gets too high. Very handy, but so far also quite expensive due to the need for external circuits and power supplies.
This project has found a way to integrate printed electronics and printed solar cells with an electrochromic organic sheet, resulting in a device which can operate without batteries.
The project has shown that one square meter of an electrochromic sheet can be powered by a 5 cm stripe made of printed solar cells and transistors along the bottom, and that all components can be manufactured by the same roll-to-roll printing processes.
One of the many difficulties was to achieve a small as possible interspace between the electrodes in order to support high current. Where printed state-of-the-art electronics has an interspace of 80 micrometers (µm), the DTU researchers are now down to 10-50 µm.
Smart windows is only one application of a self-powered sheet with printed electronics. Other possibilities are clothing with flexible electronics integrated without the need of a power source. Or the use of functional organic sheets as a cheap sensor for bio-testing
An important aspect of the material side was the introduction of ultrafast optical characterization of the materials. This new characterization technique in the field of printed electronics will allow a better control of the quality in the process of printing, and therefore a better production line.
