Midsummer reduces CIGS active layer to 800nm


While the challenges facing PV equipment suppliers remain, technological development is continuing in both the crystalline silicon (c-Si) and thin film space. The latest announced from Midsummer claims that by reducing its CIGS absorber layer to 800nm, costs and deposition times can be reduced.

Midsummer claims to have achieved conversion efficiencies of 16.7%, on a 156mm square cell, using the 800nm thick CIGS absorber. The firm says competitor processes require an absorber layer with a thickness of 2000nm (2 micron). German research body ZSW currently holds the CIGS cell conversion efficeincy of 21.7%, on a 5mm squared cell.

“By halving the thickness of the CIGS… [active layer] the manufacturing cost will be significantly reduced, which further strengthens the business case”, said Sven Lindström, CEO Midsummer, in a statement announcing the result. “Considering that the solar cell is made on stainless steel substrates, contains no cadmium buffer layer and that the production process is an all-dry, all vacuum process where all layers (including the buffer layer) are deposited by sputtering, this achievement by our engineers is truly impressive.”

Midsummer has developed its roll-to-roll deposition process since 2004, drawing on its founders’ experience in the optical disk equipment supply industry. The Midsummer process sees “cells” punched out from stainless steel roll, onto which its CIGS absorber layer is deposited, through a sputter process.

The company is also developing a back contact process that will reflect photons that have passed through the active layer, in a method not dissimilar to PERC technology in the c-Si space.

“Our scientists are constantly working on reducing the thickness and they will now start to work on this opportunity. As soon as we are done we will report it,” said Midsummer CEO Lindström.

Deloitte award

Earlier this month Midsummer was names as one of the world’s 50 fastest growing Swedish technology companies. It had picked up the award previously, in 2012.

Reflecting the difficult PV equipment supply market, Midsummer registered a loss in 2012, but returned to profit in 2013. The company reported income of SEK43.5 million (US$ 4.7 million) in 2013, with a before-tax profit of SEK10.1 million ($1.09 million).

Midsummer’s Lindström said the shift in the PV market away from PV power plants and towards rooftop applications suits its flexible technology.

“The photovoltaic market is facing a paradigm shift,” said Lindström. “Fewer large solar energy parks are being built. Instead, focus is moving towards installations in large buildings in cities. The lightweight and flexible thin film solar cells are ideal for this use. It is economically and environmentally more beneficial to use solar energy locally, where it is produced.”

Cells produced on Midsummer’s equipment can be encapsulated in flexible material, allowing it to be employed on roofs in which weight is an issue. Global Solar and MiaSolé both attempted to commercialize flex modules, before being acquired by Hanergy. Midsummer has supplied flexible modules for transport applications, such as on in buses, in Europe.

Midsummer lists use cases for its flexible modules as including: “floating modules, vehicles, landfills, portable power generation and membrane roofs on factors, office and other structures.”