Recent developments in dye sensitized solar cells (DSCs) have led to record-breaking cell efficiencies and speculation as to when, if ever, this technology will be commercially available. Generally, for residential solar or commerical solar installations you have a choice between two solar technologies. These are crystalline solar panels, the solid black/blue panels on people's roofs, and thin film solar panels, the foldable and rollable panels that are not mounted. DSCs are a third kind of solar cell that was inspired by photosynthesis, the process through which trees harness solar energy. Amazingly these cells can be sprayed or painted onto any surface and can produce electricity from diffused light, which means orientation isn't as big a concern! If we could make cheap and efficient DSCs it would revolutionize how we get solar electricity.
Two papers, by research teams at Northwestern and RMIT, present new techniques that improve the design of DSCs, bringing them one step closer to the market. According to a study by Jongyun Moon et al., the recent volume of research "indicates the importance of DSC technology as a future ubiquitous source of electricity".
There are three generations of solar cells. You can think of them as follows: first generation cells are crystalline, second generation cells are thin film and third generation cells are the rest. DSCs are one of the most promising third generation cells. Discovered in 1991 by Michael Grätzel, these cells often use titanium dioxide (TiO2), a naturally occurring and widely used pigment, instead of silicon. This is significant due to the increasing cost of silicon wafers. Also production methods DSCs are much less expensive than those of crystalline cells. So, if dye-sensitized cells ever become commercially available chances are they will be a lot cheaper than the solar panels we have today.
Unfortunately, DSCs have two major drawbacks. Chang from the Northwestern group writes that "typical dye-sensitized solar cells suffer from durability problems that result from their use of organic liquid electrolytes ... which causes serious problems such as electrode corrosion and electrolyte leakage". This means that current DSCs don't last very long. In addition, they simply don't produce enough electricity yet. Both of the new studies outline ways to overcome these issues.
The cell designed by Chang and his colleagues has two benefits. First, it can absorb more light and hence produce more electricity. The paper explains that the record was reached by increasing "visible light absorption on the red side of the spectrum". Second, it has more solid components, which makes the cell less likely to leak and thus more durable. In a Northwestern press release Mercouri Kanatzidis describes the group's solid-state cell: "The Grätzel cell is like having the concept for the light bulb but not having the tungsten wire or carbon material. We created a robust novel material that makes the Grätzel cell concept work better. Our material is solid, not liquid, so it should not leak or corrode." The cell, which uses a thin-film compound made up of cesium, tin and iodine, achieved a whopping (for DSCs) 10.2% efficiency.
While the landmark solar cell designed at Northwestern uses a semi-conductor doped with TiO2, RMIT's dye sensitized solar cell takes a novel approach by using a niobium pentoxide (Nb2O5) semi-conductor. The group reports that their cell "has a significantly higher efficiency (4.1%) when compared to that which incorporates a titanium dioxide nanotubular layer (2.7%)". This shows that this idea might be used to further improve the cell designed by Chang et al.. ABS Science reports that this material "generates a higher voltage when it receives energy from its dye coating, thus increasing the overall efficiency of the solar cell by 30 per cent."
Despite recent successes in the laboratory, it remains unclear when we will see commercial DSC products. So far, DSCs have been losing the efficiency game to other solar cells and long-term dye stability remains a serious problem. Though it may be a while before we are putting these cells on everything in sight, the recent breakthroughs are a sign that the third generation of solar cells have a fighting chance to make it to future commercial markets. For further discussion on the future of DSCs, please see this IEEE interview with Michael Grätzel.
