Shallow defects in Cu_2ZnSnS_4

摘要

Cu2SnZnS4 is a promising candidate for thin film solar cells with absorbers made of non-toxic and abundant elements. So far very little effort has been put into understanding the basic material properties. We investigate vapour phase grown Cu2SnZnS4 crystals by temperature and intensity dependent photoluminescence measurements.We observe for the first time narrow photoluminescence peaks, which allow us to determine defect levels and to propose a defect recombination model for Cu2SnZnS4. Assuming an exciton binding energy of 10 meV, we find an energy gap of 1.519 eV at 10 K.From the observed DA transitions we derive the energies of two shallow acceptor states 1075 and 3075meV above the valence band and one shallow donor state 573meV below the conduction band.