Approaching the Limits of Solar Cell Conversion Efficiency

David Lawrence is a longtime Shell Upstream Americas executive who played a vital role in Shell’s exploration and business development efforts. In early 2014, David Lawrence accepted a position as Chairman of the external advisory board of the Yale Climate and Energy Institute. The Institute promotes research and discussion of current developments in the areas of climate change and technology. A recent article looked at how we are approaching the limits of solar cell conversion efficiency.

This ultimate limit was defined in the early 1960s by William Shockley, the co-inventor of the transistor and a Nobel Prize winner. He hypothesized that the limit would be reached when the photons absorbed from, and emitted to, the sun reached a perfect balance. Research from the California Institute of Technology suggests that today’s highest-efficiency gallium-arsenide (GaAs) solar cells are now approaching this limit. The venture company Alta Devices has achieved a conversion efficiency of approximately 29.1 percent with its latest GaAs cell, which is still a distance from the predicted 33 percent ultimate limit. However, a technique of restricting light exit and entry to a narrow angle holds the promise of boosting efficiency further, enabling the long-predicted limit to be reached.

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