MaWi-Kolloquium (Hybrid)

Prof. Dr. Susanne Siebentritt

Laboratory for Photovoltaics
Department of Physics and Materials Science
University of Luxembourg

Stable Wide Gap Chalcopyrites for Tandem Solar Cells

Solar power stations provide already today the lowest levelized cost of electricity. To further improve sustainability and cost of photovoltaic systems, a continuous improvement of cell efficiency is needed. The by far major technology on the market is based on Si wafers. These solar cells have been improved so much, that they are close to their theoretical limits. To keep improving the efficiency, new technologies are needed. The next step is expected to be tandem solar cells, where a wide gap solar cell is placed on top of a Si bottom cell, thereby reducing thermalisation and non-absorption losses.

The selenide chalcopyrites Cu(InGa)Se₂ have demonstrated decades of field stability. The sulfide version Cu(InGa)S₂ offers band gaps in the range needed for top cells in tandem devices. By care-fully optimising the absorber preparation and contact layers of these solar cells, an efficiency above 16% has been achieved. This efficiency needs further improvement to enable use as a top cell. Non-radiative recombination in the absorber bulk remains a main concern. Therefore, current efforts are concentrating on two issues: (i) further improving absorber quality by doping with alkalis and by alloying with silver and (ii) using transparent conductive oxides instead of a metal as back contact, to prepare semi-transparent solar cells. The talk will discuss the opportunities and challenges of these developments.

Alle Interessierten sind herzlich eingeladen.
All interested colleagues are cordially invited.