title: Stable ultrathin partially oxidized copper film electrode for highly efficient flexible solar cells.
abstract: Advances in flexible optoelectronic devices have led to an increasing need for developing highly efficient, low-cost, flexible transparent conducting electrodes. Copper-based electrodes have been unattainable due to the relatively low optical transmission and poor oxidation resistance of copper. Here, we report the synthesis of a completely continuous, smooth copper ultra-thin film via limited copper oxidation with a trace amount of oxygen. The weakly oxidized copper thin film sandwiched between zinc oxide films exhibits good optoelectrical performance (an average transmittance of 83% over the visible spectral range of 400-800 nm and a sheet resistance of 9 Ω sq(-1)) and strong oxidation resistance. These values surpass those previously reported for copper-based electrodes; further, the record power conversion efficiency of 7.5% makes it clear that the use of an oxidized copper-based transparent electrode on a polymer substrate can provide an effective solution for the fabrication of flexible organic solar cells.
authors.affiliation: Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials, School of Materials Science and Engineering, Shandong University, Jinan 250061, China.|Division of Surface Technology, Korea Institute of Materials Science, Changwon, Gyeongnam 641-831, Republic of Korea.
authors.forename: Guoqing
authors.initials: G
authors.lastname: Zhao
authors.affiliation: Institute of Hybrid Materials, The Growing Base for State Key Laboratory, Qingdao University, Qingdao 266071, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.affiliation: Jeonju Center, Korea Basic Science Institute, Jeonju, Jeonbuk 561-180, Republic of Korea.
authors.forename: Tae-Sung
authors.initials: TS
authors.lastname: Bae
authors.affiliation: Daegu Center, Korea Basic Science Institute, Daegu 702-701, Republic of Korea.
authors.forename: Sang-Geul
authors.identifier: http://orcid.org/0000-0003-0471-7511
authors.initials: SG
authors.lastname: Lee
authors.affiliation: Division of Surface Technology, Korea Institute of Materials Science, Changwon, Gyeongnam 641-831, Republic of Korea.
authors.forename: ChaeWon
authors.initials: C
authors.lastname: Mun
authors.affiliation: Division of Surface Technology, Korea Institute of Materials Science, Changwon, Gyeongnam 641-831, Republic of Korea.
authors.forename: Sunghun
authors.initials: S
authors.lastname: Lee
authors.affiliation: Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials, School of Materials Science and Engineering, Shandong University, Jinan 250061, China.
authors.forename: Huashun
authors.initials: H
authors.lastname: Yu
authors.affiliation: Division of Commercialization Research, Korea Institute of Materials Science, Changwon, Gyeongnam 641-831, Republic of Korea.
authors.forename: Gun-Hwan
authors.initials: GH
authors.lastname: Lee
authors.affiliation: Division of Surface Technology, Korea Institute of Materials Science, Changwon, Gyeongnam 641-831, Republic of Korea.
authors.forename: Myungkwan
authors.initials: M
authors.lastname: Song
authors.affiliation: Division of Surface Technology, Korea Institute of Materials Science, Changwon, Gyeongnam 641-831, Republic of Korea.
authors.forename: Jungheum
authors.initials: J
authors.lastname: Yun