Effect of Magnesium Incorporation on Solution-Processed Kesterite Solar Cells

The introduction of the alkaline-earth element Magnesium (Mg) into Cu(2)ZnSn(S,Se)(4) (CTZSSe) is explored in view of potential photovoltaic applications. Cu(2)Zn(1−x)Mg(x)Sn(S,Se)(4) absorber layers with variable Mg content x = 0…1 are deposited using the solution approach with dimethyl sulfoxide solvent followed by annealing in selenium atmosphere. For heavy Mg alloying with x = 0.55…1 the phase separation into Cu(2)SnSe(3), MgSe(2), MgSe and SnSe(2) occurs in agreement with literature predictions. A lower Mg content of x = 0.04 results in the kesterite phase as confirmed by XRD and Raman spectroscopy. A photoluminescence maximum is red-shifted by 0.02 eV as compared to the band-gap and a carrier concentration N(CV) of 1 × 10(16) cm(−3) is measured for a Mg-containing kesterite solar cell device. Raman spectroscopy indicates that structural defects can be reduced in Mg-containing absorbers as compared to the Mg-free reference samples, however the best device efficiency of 7.2% for a Mg-containing cell measured in this study is lower than those frequently reported for the conventional Na doping.