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IBM CZTS conversion efficiency breaks world record

The firm's latest solar cell contains abundantly available materials and goes beyond 11 percent efficiency. IBM says CZTS could compete with CIGS and CdTe in the future as the latter two compounds contain rare and expensive elements
Energy from the sun reaching the earth’s surface amounts to several thousand times our global consumption of electricity.

But electricity from photovoltaic (PV) solar cells currently contributes a lot less than one percent of worldwide production. And according to photovoltaic scientists Teodor Todorov and David Mitzi at IBM Research, none of the numerous existing PV technologies have been efficient, cheaply scalable as well as come from abundantly available materials.

Until now.

IBM’s Materials Science team has partnered with Solar Frontier, Tokyo Ohka Kogyo (TOK) and DelSolar to develop an efficient and affordable PV cell made of abundant natural materials.

The collaboration has manufactured and tested Cu2ZnSn(S,Se)4 (made of 3retcopper, zinc, and tin, and referred to as CZTS) thin-film devices. The researchers say that they achieved a world-record PV solar-to-electric power conversion efficiency of 11.1 percent (10 percent better than any previous reports) for this class of semiconductors.

And the material can be manufactured by simple ink-based techniques such as printing or casting.

According to IBM, CZTS offers several advantages over competing technologies such as the most widespread PV semiconductors, made of crystalline silicon, which are abundant and highly efficient. Such silicon panels are used for everything from home electricity to the International Space Station. However, they have extremely high material purity requirements ( over 99.9999 percent!), and the wafers are typically cut from large solid ingots and wired in series to form PV modules making them expensive and difficult to upscale.

IBM's CZTS Solar Cell Device

Other thin-film chalcogenide materials used in PV cells, such as Cu(In,Ga)(SSe)2 (CIGS) and CdTe, have been developed to a performance level close to that of silicon, with inherently more scalable processing. They are directly deposited on large-area, low-cost substrates such as glass, metal or plastic foil.

While CIGS and CdTe are easy to integrate into buildings and consumer products, their compounds contain rare and expensive elements that increase cost and limit their manufacturing levels to less than 100 GW per year (worldwide continuous electricity consumption is 15 Terawatts - apparently 150 times greater than the level of what these CIGS can produce).

IBM says its CZTS PV cells could potentially yield up to 500 GW/year – coming closer to the Terawatt levels of renewable electricity the planet needs.

The focus of the joint-development team remains to further increase this device efficiency and transfer the technology to environmentally-friendly, high-throughput industrial manufacturing. The hope is that within several years this new class of photovoltaic materials will begin to contribute to the wider availability of lower-cost solar electricity.

More details of this work have been published in the paper,"Beyond 11% Efficiency: Characteristics of State-of-the-Art Cu2ZnSn(S,Se)4 Solar Cells," by Teodor K. Todorov et al, in Advanced Enegy Materials, published online on 16th August 2012.  DOI: 10.1002/aenm.201200348

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