CIGS-based thin film solar cells

CIGS is an acronym for Cu(In,Ga)Se2. This semiconductor material is an excellent light absorber, which is auto-doped and high quality CIGS is therefore always p-type. In order to use CIGS for solar cells, it needs to be combined with several other materials for making a pn-junction, for contacting and for passivation. A typical build-up of a solar cell is shown in the image below. On top of a substrate, a back contact is deposited. The CIGS layer is deposited using co-evaporation or sputtering. A buffer layer is used to form a good interface and pn-junction and on top a transparent conducting window layer is deposited.

The research aims to achieve as high efficiency as possible by using different materials and combinations of the materials as well as altering the manufacturing process. Two examples of areas we are working in consider the use of cadmium and indium. Cadmium is used in the form of cadmium sulfide (CdS) in the thin buffer layer, and since cadmium is a toxic heavy metal it is something you would want to avoid. The layer is so thin (~50 nm) that the concentration is regarded as completely safe if you for example grind the old CIGS-solar cells, but the cadmium management at the production can still be a problem. Therefore we aim to replace the CdS-layer with other buffer layers without Cd without losing in efficiency. Indium is a rare metal that limits the potential production of CIGS-solar cells with its scarcity. For example, it would not be possible with the technology today to produce enough CIGS-solar cells for the world’s electricity consumption since the known resources would not be sufficient. We are trying to develop solar cells with significantly thinner CIGS-layer with maintained efficiency, which also would lead to a decreased time for depositing and faster manufacturing.

The CIGS research on Uppsala University was also the basis for the spin-off company Solibro AB. Solibro still develops larger scale solar cells at Ultuna in Uppsala as a part of Solibro GmbH, which is one of the world’s leading manufacturers of CIGS thin film modules with headquarters in Germany. Furthermore, CIGS modules from Solibro GmbH has been installed at Frodeparken in Uppsala.

Contact: Marika Edoff

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