High efficiency Cu2ZnSnS4 nanocrystal ink solar cells through improved nanoparticle synthesis and selenization

In this work we present the improved efficiency of nanocrystal ink based Cu₂ZnSn(S, Se)₄ (CZTSSe) solar cells to 9.15%. CZTSSe devices prepared from nanocrystal inks are known for the presence of an unintended amorphous/fine-grained layer (unsintered layer) near the back contact. We demonstrate the ability to reduce the proportion of the unsintered layer in the final film through improved nanocrystal synthesis techniques and tailored thermal annealing in selenium atmosphere (selenization). Interestingly, our selenization process has not led to similar device performance in films prepared from particles using other recipes from the literature.