Correlation of the Structural and Optoelectronik Properties of Grain Boundaries in Cu(In,Ga)Se2

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Chalcopyrites are fascinating materials with regard to their application as absorbers in the most advanced thin film solar cell technology and with regard to their interesting defect and phase behavior. Grain boundaries play an important role in these polycrystalline devices. Several models for their electronic structure and their role in the device are being discussed. The peculiar phase behavior of these Materials will also influence the properties of their grain boundaries. A detailed investigation of grain boundaries has so far been hampered by the small size of the grains and their random orientation in polycrystalline films. This project aims at the epitaxial growths of films with grains of macroscopic size to provide material for the detailed investigation of the structural and optoelectronic properties of the grain boundaries. The large grains that will be grown will specifically allow the distinct Hall measurement of single grain boundaries and of the neighboring bulk material. The luminescence properties of the grain boundaries as opposed to the bulk material will be studied. Kelvin probe force microscopy will allow that direct investigation of band bending and electron affinity. These methods will provide a detailed model of the electronic structure of the grain boundaries, which will be correlated with their microscopic structure. The role of individual grain boundaries in devices will be studied as well. At the end these investigations will provide a much better understanding for the electronic structure of grain boundaries and their role in the device.