“Roll up the windows, honey. The battery needs charging.” Transparent solar cells could have many uses, which puts them on the alternative energy research agenda. One approach, described in the journal Chemistry of Materials [Structural dynamics and charge transfer via complexation with fullerene in large area conjugated polymer honeycomb thin films] developed by a research team from the U.S. Department of Energy Los Alamos and Brookhaven National Laboratories uses thin films of semi-conducting polymers (plastics) and fullerenes, nanoscale carbon molecules in the shape of a soccer ball (honeycomb pattern), to fabricate a light-absorbing, energy generating material.
Although this is very early stage work (that is, a long way from commercial application) the combination of polymer and fullerene looks like it can be used for relatively easy manufacturing of large scale surfaces (such as solar panels).
Shape is an important factor in this material.
“Though such honeycomb-patterned thin films have previously been made using conventional polymers like polystyrene, this is the first report of such a material that blends semiconductors and fullerenes to absorb light and efficiently generate charge and charge separation,” said lead scientist Mircea Cotlet, a physical chemist at Brookhaven’s Center for Functional Nanomaterials (CFN).
The combination of the polymer, which is a semi-conducting material whose properties generate the electrical energy from the solar energy captured by the buckyball (fullerene) structures, is transparent because the non-transparent polymer collects around the outer edges of the honeycomb (hexagon) pattern leaving most of the surface transparent. Since these are micron scale shapes (covering areas roughly 1/100th the width of a human hair), the overall effect is of transparency.
So far the research team has been able to create sheets of the film up to several square millimeters. The next step (typically a difficult step) will be to devise ways of ‘scaling’ the technology so that larger sheets can be manufactured inexpensively. The films are created by flowing droplets of water across a layer of the polymer-fullerene material. As the water is slowly evaporated, its molecules interact with the molecules of the underlying layer to self-assemble into the honeycomb pattern. This method, called water deposition, is usually well-suited for inexpensive and large scale manufacturing.
One obvious goal for transparent solar cells is energy generating windows. It would be very helpful if all the windows could contribute to the energy supply of a house. To achieve this goal, the polymer-fullerene film must be reliably manufactured in large sizes, be successfully applied to glass (or similar material), generate a usable amount of electricity, have a reasonable durability, and above all equal or beat the cost of other forms of solar panels. These requirements present formidable technical hurdles, which is why so few new approaches to solar energy make it all the way to commercial application.