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Kesterites to revolutionise low-cost solar cells

Thin-film solar cells are rapidly becoming cheap enough to compete with fossil fuels, having also come a long way with respect to efficiency increases. An international research team examined the basic semiconductor physics of new absorber materials that are friendlier to the environment than those now in common use.
Kesterites to revolutionise low-cost solar cells
Today, thin-film solar cells are based on chalcogenides such as copper-indium-gallium-selenium (CIGS) and cadmium telluride (CdTe). However, such solar cells have an inherent drawback in that they contain indium and tellurium, which are rare and expensive elements. Cadmium is also highly toxic, causing major environmental concerns.

Researchers within PVICOKEST (International cooperative programme for photovoltaic kesterite based technologies) considered an alternative absorber material for advanced thin-film photovoltaics technologies. CIGS has almost the same structure as a class of crystalline materials known as kesterites, which can contain chemicals such as copper, zinc, tin, selenium and sulphur – and no indium.

Kesterite solar cells may exhibit an efficiency that is not terribly impressive compared to its CIGS and CdTe counterparts (9.6 %). However, what makes this thin film unique is that it is made up of cheaper, abundant and more eco-friendly materials.

The PVICOKEST team successfully grew films and crystals made of ternary, quaternary and pseudo-quaternary kesterite compounds and inserted them into prototype solar cell devices. The focus was on studying how their physicochemical and structural properties impact on the solar cell performance.

Using different microscopy and spectroscopy techniques, the team shed further insight into the kesterite electronic and structural properties. In general, kesterite phase diagrams and crystal modifications present challenges. Researchers identified the main kesterite vibrational modes for different kesterite films and crystals and related them to the presence of ordered and disordered phases. They also developed a methodology for assessing zinc sulphide crystal sizes at the interfacial region between the kesterite absorber and the back contact layer.

Researchers obtained valuable information about the electronic band structure of kesterites containing tin and germanium. An interesting finding was that it is possible to engineer a bandgap in a kesterite containing tin by substituting the metal with the semiconductor germanium. This is particularly important when synthesising tandem solar cells.

Photovoltaic technologies based on kesterites can meet the cost, efficiency and sustainability requirements for mass production of solar cells. PVICOKEST research activities worked to keep Europe on the path to being a leader in solar energy.

Related information


Kesterites, solar cells, absorber materials, indium, photovoltaic
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