The group focuses on solar cells that are based on chalcogenide thin films. Light absorbing layers of the type Cu(In,Ga)(Se,S)2, Cu2ZnSn(Se,S)4 or other chalcogenides are combined in a thin film heterostructure similar as shown in Fig. 1. Research topics are:
Fig. 1: Scanning electron micrograph of a Mo/Cu(In,Ga)Se2/CdS/ZnO solar cell on glass in cross-section view. Thin layers of MoSe2 (~10 nm) and CdS (~50 nm) are not visible in the micrograph. The working principle of heterostructure solar cells is simple: Due to the asymmetric contacts (CdS/ZnO on one side and Mo on the other side) electrons and holes being the charge carriers are flowing to opposite directions. They form the photo current which can drive an electrical load.
Thin film preparation in our group uses physical vapour deposition under vacuum – a technique that is also employed in commercial production. Different elemental vapours are directed to the heated substrate (Fig. 2). Insitu monitoring techniques such as laser light scattering give a real-time signal of the growing thin-film. Different substrate types can be used. In the system of Fig. 2 only the absorber layers such as Cu(In,Ga)Se2 are prepared. Other deposition methods for the cell in Fig. 1 are sputtering (Mo, ZnO) and chemical bath deposition (CdS) which are performed in different set-ups. The thin MoSe2 layer is a reaction product of the polycrystalline molybdenum film with the selenium atmosphere.
Fig. 2: Sketch of a physical vapour deposition system for the simultaneous evaporation of different elements. Typically non-crystalline substrates are used which lead to polycrystalline film growth. Epitaxial growth requires crystalline substrates and is only occasionally accomplished for research purposes.
Last modified: March 19, 2013 14:04
(letzte Änderung: 19.03.2013, 14:04 Uhr)