Defects in semiconductors of Cu(In,Ga)(Se,S)2 family and their infl uence on effi ciency of solar cells with these materials

aim of project
Thin-layer solar cells, in which the absorbent is a compound of Cu(In,Ga)(S,Se)2 family, have greater efficiency, close to 20% and they constitute a more and more realistic alternative for photovoltaics based on silicon. Further progress of that technology is hampered by a still inadequate level of understanding of basic properties of CIGS family semiconductors, and especially the physics of defects in these materials. In this project we propose a full examination of CIGS solar cells by optical and electrical methods, which should reveal dominant reasons for efficiency losses in this type of cells of different absorbent composition. The main research methods are different variants of stationary and non-stationary connection methods (admittance spectroscopy, deep-level spectroscopy DLTS, photocapacity, CV and DLCP profi ling) and photoluminescence measurements. They will serve to determine parameters of electron defects and provide information on radiation and non-radiation recombination mechanisms which influence the efficiency of structures. Metastabilities in electrical characteristics of cells caused by lighting and voltage, extremely important and interesting from the point of view of application, will also be analyzed. Simultaneously conducted measurements of current-voltage characteristics of the studied cells will enable to discover relations between characteristic features of the defect spectrum in a given cell and their photovoltaic parameters and the dominant mechanism of carrier transport. This full approach aims at identifying sources of efficiency losses of photovoltaic conversion and at suggesting technological procedures for the prevention of them.

expected results
- Explanation of processes connected with self-occurring defects in CIGS cells, especially metastable phenomena in electrical characteristics of these connections;
- Explanation of the infl uence of absorbent composition on the defect spectrum, metastable phenomena and the mechanism of electron transport in a connection;
- Determination of the dominating mechanism of efficiency losses in connections of different types.