Annealing-induced optical-bandgap widening of Cu2ZnSnS4 thin films with observation of simultaneous increase in local-structure ordering

作者：Toyama Toshihiko^*; Konishi Takafumi; Seo Yuichi; Tsuji Ryotaro; Terai Kengo; Nakashima Yuto; Maenishi Ryuichiro; Arata Akiko; Yudate Shinji; Tsutsumi Yasuo; Shirakata Sho

来源：Japanese Journal of Applied Physics, 2015, 54(1): 015503.

DOI：10.7567/JJAP.54.015503

We achieved annealing-induced optical-bandgap widening in Cu2ZnSnS4 (CZTS), which is a promising material for use in high-efficiency thin-film solar cells, and we performed synchrotron-radiation X-ray absorption fine structure (XAFS) measurements to study the reasons underlying the widening. CZTS thin-film samples were fabricated at a low temperature of 230 degrees C via sputtering with a CZTS ceramic target followed by annealing at up to 550 degrees C. Optical absorption spectroscopy revealed optical bandgap widening when the annealing temperature was >= 350 degrees C. Compositional changes, phase separations, and lattice strains were excluded as possible reasons. XAFS measurements revealed that the radial distribution functions (RDFs) around the Zn K-absorption edge almost completely corresponded to those of a kesterite structure. In addition, the RDFs indicated that the disorder of atomic positions within 1 nm from zinc atoms tended to decrease with increasing annealing temperature, which we conclude is the primary reason for the optical-bandgap widening.

• 出版日期2015-1