30 August 2012
IBM has made great strides in the dire global quest for photovoltaics technologies that are highly efficient, relatively easy and cheaply to manufacture on a large scale, and made with earth-abundant, eco-friendly materials: The multinational technology and consulting corporation’s Materials Science team at IBM’s headquarters in New York state (US) has partnered with Solar Frontier and Tokyo Ohka Kogyo, both in Japan, and DelSolar in Taiwan to develop Cu2ZnSn(S,Se) (made of readily available copper, zinc, and tin; referred to as CZTS) thin-film devices that have achieved a world-record power conversion efficiency of 11.1%.
To create the novel, record-performing thin-film cells, IBM leveraged its expertise in semiconductor technology, materials and manufacturing in working with CZTS. “The low-cost ink-based approaches used in the study facilitated robust compositional control, which, paired with processing refinement, yielded superior material quality compared to any previous reports,” says IBM researcher Dr David Mitzi. “Still, the complex nature of the multi-element CZTS semiconductor — much less understood than crystalline silicon — offers significant potential for further improvement.”
The PV semiconductors broadly in use today are made of crystalline silicon and are expensive and difficult to upscale. And while other chalcogenide materials that have been developed successfully, such as CIGS and CdTe, have decent performance qualities and are easy to integrate into building and consumer products, their compounds still contain rare, expensive elements that limit production to less than 100 gigawatts per year.
So IBM set out to develop a CZTS PV cell that could potentially yield five times that electric power per year. And, by all accounts, they have succeeded. “No other stable solid-state PV device technology with potential for >500 gigawatts per year module production by easily scalable ink-based techniques has been demonstrated to date,” Mitzi says. “This potential amount of solar electricity is getting closer to the terawatt levels of renewable electricity the planet needs.”
In fact, the record efficiency the IBM team achieved in their experiments is 10% better than any previous designs with this class of semiconductors. What is more, these thin-film PV devices can be manufactured by simple ink-based techniques such as printing or casting.
The impact of IBM’s advancement on the future of thin-film photovoltaics is twofold, Mitzi predicts: “It continues to point to the potential of CZTS material to deliver truly significant amounts of solar electricity within a modest development time frame. Secondly, it will motivate scientists to think ‘outside the box’ of the current mainstream PV technologies, which typically involve expensive vacuum-based fabrication routes, and search for new less understood earth-abundant materials that can be fabricated cheaply and pervasively.”
This world record under their belt, what is going to be the next milestone for IBM Research? “One of our focus areas, as demonstrated by the recent progress, is reaching efficiency levels competitive to the much more mature CdTe and CIGS materials, which took decades of optimization by numerous outstanding research groups around the globe to reach,” Mitzi says. His device performance goal, the targeted “threshold value”, is 15%, which the researcher hopes to be able to achieve within the next five years.
Written by Sandra Henderson, Research Editor, Solar Novus Today