Fabrication and characterization of potassium-doped ZnO thin films

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Fabrication and characterization of potassium-doped ZnO thin films Sujun Guan1,* , Lijun Wang2, Yuri Tamamoto1, Mikihiro Kato1, Yun Lu3, and Xinwei Zhao1,2,4,* 1

Department of Physics, Tokyo University of Science, Tokyo 162-8601, Japan Department of Materials Science and Engineering, Xihua University, Chengdu 610039, China 3 Department of Mechanical Engineering, Chiba University, Chiba 263-8522, Japan 4 International Institute for Urban Systems Engineering, Southeast University, Nanjing 210096, China 2

Received: 7 August 2020

ABSTRACT

Accepted: 5 November 2020

To develop a simple and effective method for fabricating a type of transparent p-type zinc oxide (ZnO) thin films, potassium-doped ZnO (K-ZnO) thin films were designed and prepared via molten-salt treatment (MST) in KNO3 for n-type ZnO thin film. The influence of filming temperature during sputtering and the followed MST on the crystalline structure, transmittance, bonding environment, surface morphology, and electrical property of the ZnO thin films has been investigated. The formed compound on quartz glass could be identified as wurtzite ZnO. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results show that the crystalline quality improves with raising the filming temperature. In addition, K 2p XPS spectra hint that the outside surface of ZnO thin films contains a certain amount of K, after MST for ZnO thin films. Compared with that of the followed MST, atomic force microscope (AFM) results also show that the filming temperature significantly affects surface morphology. More importantly, the ZnO thin films obtain p-type characteristics after MST for ZnO n-type thin films, with excellent transmittance and increased mobility.

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Springer Science+Business

Media, LLC, part of Springer Nature 2020

1 Introduction In recent years of energy shortages, conversion of sunlight into a type of fuel for storing renewable energy has been significantly enticing, and the concerned photo-electrocatalytic technology

demonstrates a pathway to make effective use of solar energy [1–3]. The solar cells (SCs) with p-n homojunction have received considerable attention as a promising approach to enhance the power conversion efficiency [4–6]. Recently, Cui et al. reported their achievement in the planar p-n homojunction

Sujun Guan and Lijun Wang contributed equally to this work.

Address correspondence to E-mail: [email protected]; [email protected]

https://doi.org/10.1007/s10854-020-04847-w

J Mater Sci: Mater Electron

perovskite solar cell in 2020, showing an extremely high efficiency that exceeded 21.3%, with reduced carrier recombination losses [6]. Among the semiconductor materials, zinc oxide (ZnO) has been well widely used as a type of n-type semiconductor materials in the field of transparent conducting oxides (TCOs) in photovoltaic (PV) devices [7, 8]. The main advantages of ZnO are less resistivity, earth-rich, excellent optical, chemically stable, and nontoxic in nature. The wurtzite ZnO structure is a more common form, with a tetrahe