Low-cost, Mo(S,Se)2-free superstrate-type solar cells fabricated with tunable band gap Cu2ZnSn(S1−xSex)4 nanocrystal-based inks and the effect of sulfurization†
A low-cost and Mo(S,Se)2-free superstrate-type device structure is reported for the first time with the tunable band gap Cu2ZnSn(S1−xSex)4 nanocrystals. Using a facile hot-injection approach with only oleylamine reagent for synthesizing Cu2ZnSn(S1−xSex)4 nanocrystals with varied Se to (S + Se) ratio, the role of Se in Cu2ZnSn(S1−xSex)4 nanocrystals during the sulfurization step is systematically investigated. The loss of Sn is suppressed and the grain size is enlarged when the Se in Cu2ZnSn(S1−xSex)4 nanocrystals is replaced by S during the sulfurization. As a proof-of-concept, our superstrate-type architecture without using any binder in the ink exhibits Voc and FF comparable to the typical substrate-type device structure, in addition to its advantage of low cost.