The organic cells manufactured by researcher Ghassan Jabbour and his colleagues at the University of Arizona in Tucson have about a quarter of the efficiency of commercial silicon devices, which turn 10-20% of light energy into electricity, but being cheap to produce, can make up in quantity what they lack in quality.
The researchers print very flat, very thin cells onto glass in a similar way to conventional screen-printing. First, the glass is coated with a transparent, electrically conducting material that acts as one of the solar cell’s electrodes. On top of this, a thin film of a polymer is laid, which helps to gather current from the photovoltaic material and finally the researchers deposit a blend of two organic compounds that convert light into electricity.
One, a carbon-based molecule called a fullerene, produces charged particles that carry an electrical current when light shines onto the molecules. The other, a polymer, ferries the current to electrodes on the top and bottom of the cell.
Under blue light, these screen-printed solar cells have an efficiency of 4.3%. They are probably less efficient for white sunlight, so there is work to be done before the devices are good enough for commercial use, say the researchers.