A team of researchers led by University of Delaware researchers Christiana Honsber and Allen Barnett announced this past week that they had demonstrated a new record for the energy conversion efficiency of solar cells.  Partners in the initial phase included BP Solar, Blue Square Energy, Energy Focus, Emcore and SAIC. Key research contributors included the University of Delaware, National Renewable Energy Laboratory, Georgia Institute of Technology, Purdue University, University of Rochester, Massachusetts Institute of Technology, University of California Santa Barbara, Optical Research Associates and the Australian National University. “What we've done,” he said, “is create a virtual lab by having all of these companies, universities and national laboratories in the consortium. This has given us access to a broad range of capabilities in terms of expertise and equipment.”

The cell employs a type of hetero-junction approach, where the incident light is spectrally separated by a type of chromatic beam splitter.  The different spectral components are directed at semiconductors with different bandgaps, so that the combination utilizes are greater fraction of available incident energy.  In single-bandgap silicon structures, for example, the maximum total efficiency is only about 30%. 

The research was performed under a DARPA-supported program that aims to achieve 50% total efficiency, while maintaining about the same per-area price of solar cells today.  The researchers acknowledge that the price-point will presumably remain a great problem.  However, such high-efficiency solar cells find applications in more demanding applications, including the military, aviation, and the space sectors.  The latter in particular is extremely sensitive to weight, as every kilogram of satellite costs thousands of dollars to put into orbit. The higher efficiency would allow for smaller panels and thus reduced satellite cost.  In aviation, high-efficiency solar cells must break a barrier where enough energy can be produced per mass, so that the aircraft can remain airborne indefinitely.  Such aircraft are important for surveillance, communications, and research.

 In the next months, we will be following this DARPA program closely -- it looks like 50% efficiency goal is within reach.