Photovoltaics (LPV)

The « laboratory for photovoltaics (LPV) » is organized around the TDK Europe professorship « New materials for solar cells », which is held

We focus on two issues:

• The development of new structures and processes for the preparation of thin film solar cells and
• The fundamental materials physics of novel semiconductors used as absorbers in these devices.

We concentrate on chalcopyrites and related materials. These semiconductors are interesting from the application point of view as well as from a fundamental physics perspective.
Thin film solar cells are considered the next generation of photovoltaics because of their enormous cost reduction potential which is based on the greatly reduced consumption of material and energy and the much lower labour effort. Among the currently available technologies solar cells based on chalcopyrite (CIS) absorbers show the highest efficiencies on the laboratory scale as well as in production. We work on two preparation methods:

• electro-deposition which has a potential of low cost production since no vacuum equipment is needed
• co-evaporation which is the process used to prepare solar cells with highest efficiencies

Besides this technological interest, chalcopyrites show also unusual physical properties, concerning their phase behaviour, their electrical doping properties, their surface physics and their grain boundaries, which can be traced to the exceptionally low formation enthalpies of native defects. We study the defects in these materials by applying optical and electrical spectroscopic methods to single crystalline films prepared by epitaxy and polycrystalline films as used in the solar cells.