25 May 2011

ZSW deposits CIGS cells on polymer film in single roll-to-roll system

ZSW (Zentrum für Sonnenenergie- und Wasserstoff-Forschung — or Center for Solar Energy and Hydrogen Research — Baden-Württemberg) in Stuttgart, Germany claims that it has achieved a breakthrough in the development of efficient roll-to-roll web coating of copper indium gallium diselenide (CIGS) thin-film photovoltaic modules on plastic film.

By using lightweight, flexible substrates, the range of applications of thin-film solar cells can be increased significantly, says ZSW. Specifically, flexible thin-film solar cells on plastic film can enable many new areas of application where it is important for the cells to be both lightweight and flexible, such as solar cells on T-shirts and jackets, and modules on cars and light aircraft. It can also be advantageous to bond the solar foil to a glass substrate, since such modules would weigh half as much as standard modules (which are typically framed using two glass panels), suiting roofs that are not capable of bearing heavy loads.

However, until now, the manufacture of flexible thin-film modules has been difficult, labour intensive and time consuming, since every single layer is deposited individually in a separate system.

ZSW has been developing CIGS thin-film solar cells from the roll since 2010, using a 12m web-coating system in one of their technical labs. A temperature-resistant polyimide plastic polymer film — 0.0025cm (25µm) thick and 30cm wide — is used as the substrate. The institute had already completed the most important production steps in one go, using a continuously running system. The next phase was to complete all steps in the same system, making the manufacturing process considerably more efficient. ZSW has now combined these steps in a single system.

“The unique feature of this web-coating system is that all coating steps take place simultaneously in the same vacuum,” explains professor Michael Powalla, ZSW board member and head of the Photovoltaics Division. “While the back contact is applied at one end of the system by means of cathode sputtering, the co-evaporation of the CIGS absorber and the deposition of the transparent front contact layer are located elsewhere in the system,” he adds.

In the current development stage, the molybdenum (Mo) back contact, the four elements for the CIGS absorber, and the zinc oxide window layers can be deposited. The development and integration of a new buffer layer is still in progress. Monolithic cell interconnection will also be fully integrated at a later point in time. The goal is to produce fully integrated solar modules with even greater efficiency. ZSW has already developed CIGS thin-film photovoltaics to series production maturity in collaboration with industrial partner Würth Solar GmbH of Schwäbisch-Hall, Germany. Mass production could help to create a new generation of affordable, flexible modules, says ZSW.

The cells have already achieved a solar energy conversion efficiency of 10.2% using the web-coating system. However, using research processes, ZSW has previously produced a small, 0.5cm2 cell with a record conversion efficiency of 20.3% for a thin-film solar cell.

Development of the web-coating system by ZSW has been supported financially by the Federal Ministry for the Environment, Nature Conservation and Reactor Safety (BMU) through the CISROLL investment project.

See related items:

Swiss team claim world record efficiency for flexible CIGS solar cells on plastics

ZSW raises its thin-film solar cell efficiency record to 20.3%

Tags: CIGS solar cells CIGS solar cells on plastics

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