Optical Transmittance Enhancement of Flexible Copper Film Electrodes with a Wetting Layer for Organic Solar Cells

Guoqing Zhao, Myungkwan Song, Hee Suk Chung, Soo Min Kim, Sang Geul Lee, Jong Seong Bae, Tae Sung Bae, Donghwan Kim, Gun Hwan Lee, Seung Zeon Han, Hae Seok Lee, Eun Ae Choi, Jungheum Yun

Research output: Contribution to journalArticlepeer-review

45 Citations (Scopus)


The development of highly efficient flexible transparent electrodes (FTEs) supported on polymer substrates is of great importance to the realization of portable and bendable photovoltaic devices. Highly conductive, low-cost Cu has attracted attention as a promising alternative for replacing expensive indium tin oxide (ITO) and Ag. However, highly efficient, Cu-based FTEs are currently unavailable because of the absence of an efficient means of attaining an atomically thin, completely continuous Cu film that simultaneously exhibits enhanced optical transmittance and electrical conductivity. Here, strong two-dimensional (2D) epitaxy of Cu on ZnO is reported by applying an atomically thin (around 1 nm) oxygen-doped Cu wetting layer. Analyses of transmission electron microscopy images and X-ray diffraction patterns, combined with first-principles density functional theory calculations, reveal that the reduction in the surface and interface free energies of the wetting layers with a trace amount (1-2 atom %) of oxygen are largely responsible for the two-dimensional epitaxial growth of the Cu on ZnO. The ultrathin 2D Cu layer, embedded between ZnO films, exhibits a highly desirable optical transmittance of over 85% in a wavelength range of 400-800 nm and a sheet resistance of 11 Ω sq-1. The validity of this innovative approach is verified with a Cu-based FTE that contributes to the light-to-electron conversion efficiency of a flexible organic solar cell that incorporates the transparent electrode (7.7%), which far surpasses that of a solar cell with conventional ITO (6.4%).

Original languageEnglish
Pages (from-to)38695-38705
Number of pages11
JournalACS Applied Materials and Interfaces
Issue number44
Publication statusPublished - 2017 Nov 8

Bibliographical note

Funding Information:
This research was funded by the New & Renewable Energy Core Technology Program of the Korea Institute of Energy Technology Evaluation and Planning supported by the Ministry of Trade, Industry & Energy of Korea and the Fundamental Research Program of the Korea Institute of Materials Science. H.-S.C. was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Science, ICT and Future Planning (MSIP) of Korea (No. 2015R1C1A1A01052727).

Publisher Copyright:
© 2017 American Chemical Society.


  • copper
  • flexible transparent electrode
  • organic solar cell
  • ultrathin film
  • wetting layer

ASJC Scopus subject areas

  • General Materials Science


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