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Open Access Nano Express

Optimization of dye adsorption time and film thickness for efficient ZnO dye-sensitized solar cells with high at-rest stability

Wei-Chen Chang12, Chia-Hua Lee2, Wan-Chin Yu1* and Chun-Min Lin1

Author Affiliations

1 Institute of Organic and Polymeric Materials, National Taipei University of Technology, Taipei, 10608, Taiwan

2 Green Energy and Environment Research Laboratories, Industrial Technology Research Institute, Hsinchu, 31053, Taiwan

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Nanoscale Research Letters 2012, 7:688  doi:10.1186/1556-276X-7-688

Published: 28 December 2012

Abstract

Photoelectrodes for dye-sensitized solar cells were fabricated using commercially available zinc oxide (ZnO) nanoparticles and sensitized with the dye N719. This study systematically investigates the effects of two fabrication factors: the ZnO film thickness and the dye adsorption time. Results show that these two fabrication factors must be optimized simultaneously to obtain efficient ZnO/N719-based cells. Different film thicknesses require different dye adsorption times for optimal cell performance. This is because a prolonged dye adsorption time leads to a significant deterioration in cell performance. This is contrary to what is normally observed for titanium dioxide-based cells. The highest overall power conversion efficiency obtained in this study was 5.61%, which was achieved by 26-μm-thick photoelectrodes sensitized in a dye solution for 2 h. In addition, the best-performing cell demonstrated remarkable at-rest stability despite the use of a liquid electrolyte. Approximately 70% of the initial efficiency remained after more than 1 year of room-temperature storage in the dark. To better understand how dye adsorption time affects electron transport properties, this study also investigated cells based on 26-μm-thick films using electrochemical impedance spectroscopy (EIS). The EIS results show good agreement with the measured device performance parameters.

Keywords:
Zinc oxide; Dye-sensitized solar cells; Dye adsorption time; Film thickness; Conversion efficiency; At-rest stability; Electrochemical impedance spectroscopy