High efficiency, high voltage solar cells by band gap and defect engineering in Cu(In, Ga)(S,Se){sub}2 chalcopyrite semiconductors

摘要

High band gap chalcopyrite solar cells, e.g., based on CuInS{sub}2 or CuGaSe{sub}2, are limited to much lower efficiencies as compared to their lower-band gap counterparts especially the alloy Cu(In,Ga)Se{sub}2. This contribution analyses the actual limitations, especially those opposed by bulk defects and discusses ways how to overcome them and shows that it is possible to achieve open circuit voltages as high as 894 mV with CuGaSe{sub}2 and 840 mV with the pentenary alloy Cu(In,Ga)(S,Se){sub}2. We discuss ways how to minimize defect concentrations in the chalcopyrites by proper alloying and/or surface treatments. Alternatively, a way to come along with the usually high defect concentrations in wide-gap chalcopyrites is to engineer the band gap through the absorber by alloying in a way that a high band gap energy exists where the recombination probability is high. The potential of band gap engineering and its limitations are discussed in the framework of numerical simulations in comparison to experimental results.