Optimization of a Zinc Oxide Photoelectrode for Dye-Sensitized Solar Cells
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Optimization of a Zinc Oxide Photoelectrode for Dye-Sensitized Solar Cells Jeongsoo Hong∗ Department of Electrical Engineering, Gachon University, Seongnam 13120, Korea (Received 22 June 2020; revised 11 August 2020; accepted 12 August 2020) In this study, the influence of the seed-layer thickness of photoelectrodes on the performance of dye-sensitized solar cells was investigated. Al-doped ZnO films deposited on fluorine-doped tin oxide substrates by using facing targets sputtering systems of various thicknesses were used as seed layers, and ZnO rod array photoelectrodes were synthesized on the AZO seed layers via the hydrothermal process. The crystallinity of the ZnO photoelectrode was improved, and the average diameter of the ZnO rod increased from 100 ± 10 to 250 ± 10 nm as the thickness of the seed layer increased from 200 to 600 nm. The maximum fill factor, open-circuit voltage, current density, and power conversion efficiency of the ZnO rod array photoelectrode with a seed layer of thickness 600 nm were 31.08%, 0.53 V, 5.53 mA/cm2 , and 0.91%, respectively. Keywords: ZnO, Photoelectrode, Seed layer, FTS, Hydrothermal DOI: 10.3938/jkps.77.924
I. INTRODUCTION Zinc oxide (ZnO) is an n-type semiconductor material. It has a wide bandgap (3.37 eV at 298 K) and a large exciton binding energy (60 meV). ZnO has been investigated for various electronic applications, including solar cells, gas sensors, piezoelectric sensors, and light-emitting diodes [1–6]. Among them, ZnO-based dye-sensitized solar cells (DSSCs) have attracted much interest due to the high carrier mobility and ease of synthesis of ZnO photoelectrodes [7]. In addition, a ZnO rod array has good electron transport properties [8]. Various deposition techniques are used for growing ZnO rod array, among which metal-organic chemical vapor deposition (MOCVD) is commonly employed [9]. However, MOCVD is a high-temperature deposition process; thus, employing it flexible electronics is difficult. On the contrary, solution-based processes, including the hydrothermal process, have many advantages, such as simplicity of the synthesis process and low cost. In addition, the crystallographic and the morphological properties of the ZnO rod arrays can be easily controlled via the solution-based processes [1]. In this work, we studied the optimized conditions for ZnO photoelectrode for DSSCs fabricated via solutionand vacuum-based processes. If an optimized ZnO photoelectrode is to be fabricated, various conditions, including seed layer and temperature, should be considered as they are among the factors that affect the electron mobility of the resulting photoelectrodes, which affects the performance of the DSSCs. The influence of the thick∗ E-mail:
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pISSN:0374-4884/eISSN:1976-8524
ness of the seed layer on the performance of ZnO photoelectrodes for DSSCs was investigated. Al-doped ZnO (AZO) films of various thicknesses were deposited on fluorine-doped tin oxide (FTO) substrates, which were used as the seed layers for the ZnO rod array photoelectro
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