Industry is steadily marching the cost of current photovoltaic technology downwards and it appears likely that photovoltaics will become competitive across most markets in the coming years and decades [1]. Many of these cost reductions will come from improvements in manufacturing, installation and in smoothing the permitting process rather than improvements in basic science [2]. This is good news for those of us yearning for a renewable energy infrastructure.

While current technologies are making their way to markets, researchers in basic science already have their eye on the next generation of technologies that will make photovoltaics even more efficient and competitive.

The efficiency of a photovoltaic cell describes the ratio between energy contained in the electricity generated by the cell to the energy of sunlight on the cell. Thermodynamics limits exist for the efficiency that no amount of innovation can overcome. This maximum theoretical efficiency is known as the Shockley-Queisser limit [3] and is only 33.7%, for the simplest photovoltaic architectures, known as single-junction devices. We would like to be build cells that operate at the thermodynamic limit, but in practice even the best research grade cells under-perform. Manufactured cells generating electricity in the market today typically only operate at an efficiency of 10-20%.

One well known mechanism to improve the overall efficiency is to couple several simple devices together into what is known as a multi-junction device. Today the best research grade multi-junction cell is 43.5%, a significant improvement. A recent commentary in Nature Materials[4] outlines a set of proposals for doing even better. The authors argue that recent innovations in the control of light made possible by nanotechnology, such as nano-sized optics, should allow us to not only build better multi-junction devices but also move closer to the thermodynamic limit for single-junction devices. Combined they argue that their plan could allow us to build devices with efficiencies between 50-70%.  Such an improvement would mean that for equally sized modules, 2.7 to 7 times more electric power could be generated compared to today’s photovoltaic modules.

So while industry continues to push costs of today’s technology down towards mainstream adoption, scientists and engineers around the world are already planning and developing new technologies that will lead to even more efficient, more competitive photovoltaic modules in the coming years.

-Joshua LaForge, PhD Candidate in Electrical and Computer Engineering Department, University of Alberta

Josh LaForge

[1] Technology Roadmap — Solar Photovoltaic Energy (International Energy Agency, 2010); http://www.iea.org/papers/2010/pv_roadmap.pdf

[2] Alan Goodrich, Ted James, and Michael Woodhouse. Residential, Commercial, and Utility-Scale Photovoltaic (PV) System Prices in the United States: Current Drivers and Cost-Reduction Opportunities. NREL Technical Report. February 2012. NREL/TP-6A20-53347

[3] Shockley Queisser Limit. Wikipedia. http://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limit

[4] Polman, A., & Atwater, H. a. (2012). Photonic design principles for ultrahigh-efficiency photovoltaics. Nature materials, 11(3), 174–7. doi:10.1038/nmat3263

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