Effect of Double Cation Substitution on Nonradiative Recombination Losses in Cu2ZnSn(S,Se)4 Solar Cells

Recent developments in kesterites encouraged the researcher to use Cu2ZnSn(S,Se)4 (CZTSSe) based photo absorber materials in diverse optoelectronic applications. However, the detrimental bulk and interface defects induced high carrier recombinations at corresponding regions stagnated further improvement in the device performance of kesterite solar cells. The present work demonstrates a facile Silver (Ag) and Germanium (Ge) incorporation approach to cure these defects. The Ag incorporation mainly reduced the interface defect states, whilst the Ge incorporation mainly cures the deep-level defect states, suppressing the carrier recombination within the space charge and quasi-neutral regions. As a result, an improved carrier separation process, minority carrier lifetime, and reduced nonradiative carrier recombination losses increased device performance by more than 20%. Finally, the champion device with double cation incorporation of Ag and Ge in the CZTSSe absorber layer delivers enhanced device performance from 9.11 to 11.32%.