Cross-section of copper-zinc-tin chalcogenide photovoltaic devices.
At present, although the solar panel market (18.2 GWP produced in 2010) is dominated by crystalline silicon solar cells, thin-film solar cell technology based on chalcogenide (S, SE and TE) will greatly increase their market penetration. For example, First Solar will produce 1.5 billion watts of cadmium telluride (CdTe) components in 2010, and it is estimated that it will reach 2.3 billion watts by the end of 2011. Other cadmium telluride companies, such as Primestar, belong to energy giant General Electric, which is accelerating cadmium telluride production, and many other companies, such as Solar Frontier, Mia sole, Ascent, Nano Solar and others are all focusing on copper indium gallium (DI) selenide (CIGS) solar cells. Copper indium gallium selenide has the potential to achieve higher efficiencies, and laboratory-scale equipment efficiency has reached 20.3%.
In addition to equipment performance, price fluctuations (especially indium), rare earth scarcity issues (such as helium), and potential environmental issues (such as cadmium toxicity) have caused some people to worry about cadmium telluride and copper indium gallium. selenium. The next generation of thin-film PV materials to be found is the quaternary copper-zinc-tin-sulfide (CZTS) and the copper-zinc-tin-chalcogenide (CZTSSe). It is worth noting that these materials contain abundant natural elements in the earth's crust and have very low toxicity.
“Historically, most of the synthesis of quarter copper-zinc-tin-sulfur thin-film solar cells uses vacuum deposition of metal precursors followed by vulcanization,†says Hugh W. Hillhouse, who is Dr. Rehnberg, professor of chemical engineering at the University of Washington. "However, this approach is challenging because of the cost, spatial heterogeneity, and the resulting binary compounds, such as zinc sulfide (ZnS). Therefore, they are developing some solution-based inorganic solar cell chemistry technologies. To significantly reduce production costs and improve performance."
The current record is that the photoelectric conversion efficiency of copper-zinc-silicon-sulfur solar cells exceeds 10.1%. This record was produced by colleagues of Mitzi and IBM ("High-efficiency solar cells use absorbent liquids on Earth's abundance".) The precursor used needs to be stabilized with hydrazine, a hepatotoxic, explosive carcinogenic solvent.
A paper was published in the latest issue of "Advanced Energy Materials", which reads "Earth-Abundant Element Photovoltaics Directly from Soluble Precursors with High Yield Using a Non-Toxic Solvent, Hillhouse and his team showed that there are other chemical methods that use more benign solvents, which need to demonstrate a simple and lightweight solution phase method to make the season Copper-zinc-tin-sulfur thin-film solar cells can also be produced at high yields using commercially available precursors and non-toxic solvents.
In this work, a key finding is that there are some alternatives so that nanocrystalline inks or toxic solvents such as hydrazine can no longer be used to produce highly efficient solution-processed solar cells.
"In fact, there is a possibility for the solution processing of inorganic solar cells, and we are likely to just catch the surface," said Hillhouse.
His superficial new chemical method for the preparation of copper-zinc-tin chalcogenide thin-film solar cells requires the use of a spin-on solution, a highly soluble, inexpensive commercial precursor, and an environmentally friendly non-toxic solvent, namely dimethyl sulfoxide. (dimethyl sulfoxide). In this way, a high quality copper zinc tin chalcogenide film can be formed and subsequently selenization on molybdenum-coated sodalime glass. The fabricated solar cell device has air stability, exhibiting an efficiency of 4.1%.
Hillhouse pointed out that from the precursor to the film, the amount of metal blended in this way can be close to 100%. This is not the case with the nanocrystalline ink method, but it can be made with an efficiency of 7.2%.
This novel method of processing opens the door to the production of thin-film solar cells that are produced at low cost using solution processing, using the rich elements of the earth. The absorber layer can be deposited using a slot die coating, a partition coating, or other process that can be easily upgraded.
"So far, little is known about this basic electronic property, defect physics, thermodynamics, or the kinetics of the formation of quaternary copper, zinc, and tin, and even less understanding of the heterostructure-based optoelectronic devices based on copper, zinc, and sulfur. Said Hillhouse. "The theoretical efficiency limit of single-junction solar cells, using quarter copper, tin, sulfur or copper zinc tin and chalcogenide is more than 30%. It is very likely that once these basic conditions are in place, the quarter copper, tin, and sulfur solar cells can one day replace copper indium gallium. Selenium, cadmium telluride, and even silicon-based photovoltaic technology."