Harnessing Solar Energy with Organic Photovoltaics

Solar energy is one of the most attractive solutions to the problem of meeting our energy demand in the future. Photovoltaic cells are not yet truly competitive, but advances in organic and dye-sensitised solar cells have the potential to provide a realistic, low-cost alternative to fossil fuels.

The sun delivers more energy to earth in an hour than we use from all energy sources combined in a year¹ . Currently, photovoltaic (or solar) cells used to capture this energy are made from inorganic materials, such as silicon, cadmium telluride or copper indium selenide. The cost of these materials limits their potential to replace fossil fuels, and in order to be competitive the cost needs to be reduced by a factor of 2-5.

Organic Alternatives

Photovoltaic cells made from organic polymers, though, are a possible low-cost alternative. In addition to being cheaper, they are also lightweight and flexible, which means they could be used for a wide range of new applications. An example of a polymer used in an organic photovoltaic (OPV) is shown below². Polymers like this have higher optical absorption coefficients that the current inorganic materials.

OPVs are emerging from very recent research, often involving innovative organic synthesis. For example, the procedure used to produce the polymer above relied on a novel method of bond formation which was recognised with a Nobel Prize in 2010. The work by Professors Heck, Negishi and Suzuki is important for constructing complex organic molecules, like those used in photovoltaics.

Some way to go

However, existing solar cells based on OPVs are quite inefficient due to energy leakage, with an efficiency of around 6-8%. This will need to be improved to around 15% in order to be competitive. Researchers will have to improve cell performance and stability, along with the fabrication methods used. Providing low cost and high volume manufacturing procedures will also be vital if OPVs are to have a role in our future energy supply.

Improving the efficiency of OPVs is likely to require inspired and novel molecular design. At the same time, organic chemists will need to work as part of a multidisciplinary landscape of researchers developing new photovoltaic materials and devices, if solar cells are to fulfil their potential to provide clean, renewable energy.

References

1 Solar Fuels and Artificial Photosynthesis, Science and innovation to change our future energy options, RSC, January 2012
2 H A Atwater, A Polman, Nature Mater., 2010, 9, 205
3 J R Durrant, I McCulloch et al, J. Am. Chem. Soc., 2011, 133, 3272
4 F He, W Wang, W Chen, T Xu, S B Darling, J Strzalka, Y Liu, L Yu, J. Am. Chem. Soc., 2011, 133, 3284
5 Y Yuan, T J Reece, P Sharma, S Poddar, S Ducharme, A Gruverman, Y Yang, J Huang, Nature Mater., 2011, 10, 296
6 J E Anthony, A Facchetti, M Heaney, S R Marder, X Zhan Adv. Mater., 2010, 22, 3876