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Higher potential efficiencies in thin film PV with new CIS material

Researchers at the US Department of Energy’s Argonne National Laboratory and the University of Texas, Austin have developed a new, inexpensive material for thin-film photovoltaics that is able to capture light more effectively than standard silicon solar cells – potentially enabling higher energy conversion efficiencies.

The new material, Copper-Indium-Selenide (CIS), is closely related to the more well-known CIGS (Copper-Indium-Gallium-Selenide), which was used to make devices that currently hold the record efficiency for thin-film solar cells.

Unique properties of the new CIS material allow it to take advantage of an efficiency-boosting mechanism known as multiple exciton capture, which in theory allows conversion efficiencies beyond the well-known Shockley-Queisser limit of ~34% that standard silicon solar cells are subject to. This mechanism works by enabling the solar cell to generate more current from the more energetic blue end of the solar spectrum than standard silicon solar cells.

While the concept of multiple exciton capture is not new, studying its effects is difficult as it requires characterisation tools that are not commonly available. Thanks to specialised spectroscopic equipment available at the Argonne National Laboratory, the researchers have successfully demonstrated the potential of the energy-boosting concept in a mass-producible material like CIS.

CIS solar cells, like other thin film technologies, are advantageous from a material usage and cost standpoint as they can be made thinner than standard silicon solar cells (up to 50-100x thinner). This is because of their inherently better absorption properties, which allow them to absorb the same amount of light as a standard cell but using lesser material.

With a view to make the technology more commercially relevant, the researchers have also used a material deposition technique called photonic curing, which lends itself particularly well for large-scale manufacturing.

The breakthrough comes at a time of declining popularity of thin film PV technologies, which contribute only 10% to the total annual share of world-wide PV production. This underscores the need to develop cost-effective technologies that can compete with other, more dominant silicon-based technologies.

The importance of commercial viability on research was recognized by University of Austin Professor Brian Korgel, who stated, “The holy grail of our research is not necessarily to boost efficiencies as high as they can theoretically go, but rather to combine increases in efficiency to the kind of large-scale roll-to-roll printing or processing technologies that will help us drive down costs”.

Top image: CIS unit cell, via Wikipedia.

© 2014 Solar Choice Pty Ltd

Nitin Nampalli

Nitin is a regular contributor to Solar Choice News with a focus on solar PV technology. He holds a Master of Engineering Science in Renewable Energy from UNSW and a Bachelor of Science degree in Microelectronic Engineering from Rochester Institute of Technology, New York. He is currently a PhD candidate researching solar photovoltaics at UNSW. In addition to his studies, he has also worked extensively in solar PV research.
Nitin Nampalli