As I pointed out this week, inexpensive photovoltaics are good, but inexpensive and efficient ones are much better. For years now, the dye-sensitized solar cell (DSSC) has been one of the least expensive photovoltaic devices on the market. But even one of the inventors of the technology conceded just a couple of years ago that there needed to be a big push to improve the energy conversion efficiency of the devices.
While new manufacturing techniques have recently been proposed that should further reduce the manufacturing costs associated with producing DSSCs, a bit of a bump up in conversion efficiency would perhaps be a more welcome development.
To meet this need, researchers at the KTH Royal Institute of Technology in Sweden have developed a method for making DSSCs that are not only are more efficient but longer lasting. The foundation of the improvement is a new, quasi-liquid, polymer-based electrolyte that increases the solar cells' voltage and current and lowers resistance between electrodes.
DSSCs are essentially a photochemical system in which a photo-sensitized anode and an electrolyte form a semiconductor. In their commercial incarnation, today's DSSCs consist of a porous layer of titanium dioxde (TiO2) nanoparticles that have been covered with a molecular dye that absorbs sunlight, and a platinum-based catalyst. The TiO2 , which is immersed in an electrolyte solution that acts as a conductor, is the device's anode; the platinum, which sits atop the electrolyte, is the cathode.
A more efficient DSSC would use a material like acetonitrile for the electrolyte. However, this material does not lend itself to the production of a stable solar cell that could be commercially marketed. Instead, a low-volatility solvent is typically used, but this comes at the price of being more viscous and impeding the flow of ions.
The novel quasi-liquid electrolyte that the KTH researchers have developed delivers the best of all worlds: overcoming the viscosity problem, improving the flow of electrons, and doing so at a much lower volatility than can be achieved with acetonitrile.
“We now have clear evidence that by adding [a special] ion-conducting polymer to the solar cell’s cobalt redox electrolyte, the transport of oxidized electrolytes is greatly enhanced,” said James Gardner, a professor of photoelectrochemistry at KTH, in a press release. “The fast transport increases solar cell efficiency by 20 percent.”
With conversion efficiencies for DSSCs already having already reached the 10 percent mark, this would boost efficiency to around 12 percent.
These are impressive numbers, but perhaps a more beneficial characteristic—at least for the economics of DSSCs—would be a longer lifespan. With this new electrolyte, DSSCs could have a longer lifespan, making it possible to amortize the cost of the initial installation over a greater period of time. It's not clear how much more life could be added to the DSSCs, but every bit counts.
Photo: David Callahan