title: Role of anions in aqueous sol-gel process enabling flexible Cu(In,Ga)S2 thin-film solar cells.
abstract: Recently, environmental-friendly, solution-processed, flexible Cu(In,Ga)(S,Se)2 devices have gained significant interest, primarily because the solution deposition method enables large-scale and low-cost production of photovoltaics, and a flexible substrate can be implemented on uneven surfaces in various applications. Here, we suggest a novel green-chemistry aqueous ink that is readily achievable through the incorporation of molecular precursors in an aqueous medium. A copper formate precursor was introduced to lower the fabrication temperature, provide compatibility with a polyimide plastic substrate, and allow for high photovoltaic performance. Through a comparative spectroscopic study on temperature-dependent chemical/crystal structural evolution, the chemical role of copper formate was elucidated, which led to the chalcopyrite framework that was appropriate to low-temperature annealed Cu(In,Ga)S2 absorber layers at 400 °C. This Cu(In,Ga)S2 solar cell exhibited a power conversion efficiency of 7.04% on a rigid substrate and 5.60% on a polymeric substrate. Our cell on the polymeric substrate also demonstrated both acceptable mechanical flexibility and durability throughout a repeated bending test of 200 cycles.
authors.affiliation: Department of Materials Science and Engineering, Yonsei University , 50 Yonsei-ro Seodaemun-gu, Seoul 120-749, Republic of Korea.
authors.forename: Yunjung
authors.initials: Y
authors.lastname: Oh
authors.forename: Kyoohee
authors.initials: K
authors.lastname: Woo
authors.forename: Daehee
authors.initials: D
authors.lastname: Lee
authors.forename: Hongseuk
authors.initials: H
authors.lastname: Lee
authors.forename: Kyujin
authors.initials: K
authors.lastname: Kim
authors.forename: Inhyuk
authors.initials: I
authors.lastname: Kim
authors.forename: Zhaoyang
authors.initials: Z
authors.lastname: Zhong
authors.forename: Sunho
authors.initials: S
authors.lastname: Jeong
authors.forename: Jooho
authors.initials: J
authors.lastname: Moon
keywords: CIGS; aqueous sol−gel; flexible thin-film solar cells; low temperature processing