Although solar cells have found limited application, much development is required before they will be suitable for widespread adoption. Cheap oil means that the life-cycle efficiency of solar cells needs to be fairly high before solar electricity becomes competitive. The efficiency of solar electricity production has many bottlenecks: the production cost of the cell needs to be low, the amount of light converted to electricity needs to be high, and the total lifetime of the cell needs to be long.
In terms of making solar cells more efficient, the big problem is developing materials that are able to free up electrons in response to a wide range of light colors. To achieve this, researchers have been impregnating solar cells with dye molecules. Dye molecules already absorb light efficiently—otherwise they wouldn’t be colored. For many dyes, the process of light absorption results in an electron being temporarily lost by the dye molecule. However, the dye molecule cannot absorb more light until it recaptures an electron. This means that the solar cell needs to contain a solid electrolyte that can transport electrons back to the dye molecules relatively quickly. Typically, these dyes are used in combination with traditional solar cell materials, such as titanium dioxide, where they are said to sensitize the nanocrystalline titanium dioxide. The problem is that it is proving difficult to find a combination of dye and electrolyte that is stable. The stability of the dye molecule depends on, among other things, the speed with which it gets that electron back. Critically, electrolytes must be able to maintain the necessary current flow without reacting, and be stable in sunlight.
In the search for a good combination of dye and electrolyte, a group of researchers from India, the UK, and the USA decided to try using DNA as the electrolyte. They found that solar cells made from dye sensitized titanium dioxide in a solid DNA electrolyte were able to support short circuit currents of 660mA/m2, which is quite low. In addition, DNA isn’t that stable under illumination by UV light, so the performance decayed quite fast, dropping to about two thirds of its initial efficiency after seven days. On the other hand, using just the adenine base as the solid electrolyte resulted in solar cells that were more stable. Although the short circuit current was substantially lower, the power delivery through a load was better.
One of the reasons for pursuing this line of research is that the resulting solar cells are flexible and relatively cheap. The biggest problem is that the total efficiency is still too low, even compared to existing solar cells. However, the thickness of the solar cell was less than 50nm, which is very thin, meaning that much of the light passes straight through. The next step will be to manufacture thicker solar cells to see if they retain their stability and increase their efficiency.
Journal of Applied Physics, 2007, DOI: 10.1063/1.2781472