The future of CIGS

Thin-film has its charms. One hundredth of the thickness of crystalline silicon (c-Si), ultra-efficient and simpler to fabricate, CIGS (copper indium gallium selenide) technologies measure up well on many levels.

Price, however, remains the spoiler, with disparities in cost threatening to grow larger as conventional c-Si and market overcapacity continue to eat away at thin-film’s annual market share, which is forecast to slide from about 9% in 2013 to 7% by 2017.

Solar Frontier, which next month breaks ground on its fourth CIGS module plant in Japan — the 150MW Tōhoku factory — is bucking the trend, having shifted to an energy-provider model, rather than functioning solely as a module supplier. Together with First Solar, Solar Frontier is expected to account for 75% of thin-film sales this year.

So although manufacturing of CIS — as Solar Frontier calls CIGS — takes a third as many steps as for a c-Si cell and uses 60% less energy, the company is finding it necessary to trim costs further with a deposition method that is cheaper than the current “co-evaporation” technique used to create its crystalline layers.

A hybrid high-temperature sputtering-selenisation process is being fine-tuned that promises lower unit cost while boosting efficiencies to within reach of co-evaporation’s record-setting 20.3%. Solar Frontier has hit 19.7% in the lab.

“Our new method will compress our production cost by a significant amount,” states chief technology officer Satoru Kuriyagawa. “We are always studying how the CIS crystals are growing on the substrate and developing new ways of controlling this process to improve efficiency.”

First fruit from this cost-reduction strategy can be seen in the fact that Solar Frontier’s per-unit capacity investment at Tōhoku will be two thirds that seen in its older CIS manufacturing plants, while the speed of panel fabrication is expected to jump by about half.

Efficiencies of its thin-film have plateaued below 20%, but Kuriyagawa says his research team is now confident next-generation CIS technology can reach a game-changing 29.7%, eclipsing the accepted ceiling on CIGS efficiency of 25%.

“The major factor will be optical tuning [whereby crystal growth is engineered to improve refraction within the cell],” he states. “Another will be optimising — with new laser technology — the patterning width [distance between lines scribed into layers of a cell to hone efficiency].”

Solar Frontier calculations suggest its CIS technology can generate electricity levels 8% higher than a same-size c-Si system over the course of a year.