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Ink-jet printing is contributing to a breakthrough in the production of thin-film solar devices. Oregon State University engineers submitted a patent for a printing process and chemical solution that could significantly reduce the cost of producing solar energy cells, OSU announced today.

The new process offers a cheaper, faster and more controlled alternative to existing ones that rely on expensive technology and high-cost materials.

The focus of the study is chalcopyrite: a compound composed of copper, indium, gallium and selenium, nicknamed 鈥淐IGS.鈥� Manufacture of such solar cells typically requires expensive vacuum equipment.

鈥淭he challenge for (vacuum-based deposition) processes is that when you scale it up, you need to maintain the uniformity and quality of the film, which is challenging and expensive,鈥� said Chih-hung Chang, an OSU professor in the School of Chemical, Biological and Environmental Engineering.

Engineers have already developed solution-based approaches; however, most rely on dangerous solvents that would be difficult to apply commercially.

Chang and Wei Wang, a fourth-year student seeking his doctorate, have developed a solution-based process that is both cheap and industrially viable.

鈥淥ur process is very stable and uses a relatively benign solution,鈥� Wang said. 鈥淚t’s much healthier than other solution-based processing.鈥�

The ink is composed of low-cost metal salt such as metal chloride and acetate, which have been used in fabrication of CIGS solar cells.

The new approach also has the potential to reduce raw material waste by up to 90 percent. In other processes, most of the molecules that need to react on the surface of the solar cell don’t 鈥渟tick,鈥� so a larger amount of the compound is required, Chang explained.

In contrast, ink-jet technology creates precise patterns with little waste. Wang and Chang may be the first engineers to use ink-jet printing to deposit chalcopyrite directly onto the cell. The team recently purchased a roll-to-roll printer, which will accelerate the printing process. Wang hopes to use the new printer to demonstrate his discovery on a larger scale.

Tweaking is still needed before large-scale testing can take place, however. The working model is somewhat smaller than actual rooftop panels, so larger modules need to be fabricated and tested. Also, dust in the air has caused cracks in the cell.

鈥淚t’s kind of like mud,鈥� Chang said. 鈥淚nitially, when it’s wet, the mud looks packed and dense, but when heated up you see all of the cracks.鈥�

The major remaining issue is cell efficiency. Other vacuum-based CIGS solar cells can reach up to 20 percent power conversion efficiency, but Wang believes 15 percent may be the highest feasible efficiency for his printing technique.

Their cell functions at approximately 5 percent efficiency, but 12 percent is needed for commercial viability.

Wang was reluctant to make predictions about future marketability. Chang, however, predicted that market readiness will be achieved in approximately two years.