Impacts of ZnO/TiO 2 Assorted Electrode on Photoelectric Characteristics of Dye-Sensitized Solar Cells
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Impacts of ZnO/TiO2 Assorted Electrode on Photoelectric Characteristics of Dye-Sensitized Solar Cells Xu Wang, Haiyou Yin, Bao Wang, Lifeng Liu, Yi Wang, Jinfeng Kang* Institute of Microelectronics, Peking University, Beijing 100871, P.R. China * Email: [email protected] ABSTRACT A novel ZnO/TiO2 assorted photoelectrode for dye-sensitized solar cells (DSSCs) is proposed. The impacts of the ZnO/TiO2 assorted photoelectrode on the photovoltaic performance of dye-sensitized solar cells (DSSCs) were investigated. The measurements of the light transmission spectra showed the higher transmittance through ZnO/FTO than through FTO during the effective wavelength region of 536nm~800nm for DSSCs, indicating that ZnO/TiO2 assorted photoelectrode is beneficial for the photovoltaic performance of DSSCs. The measurements on the photovoltaic characteristics of the DSSC cell indicate that the inserted ZnO layer can cause the increased open circuit voltage (Voc) more than 70 mV and fill factor (FF) but the decreased short circuit current. The enhanced Voc and FF could be attributed to the suppressed the recombination of photon-generated carriers between the ZnO/TiO2 assorted photoelectrode and electrolyte (dye) compared to TiO2 photoelectrode. However, the additional series resistance of inserted ZnO layer causes the reduced short circuit current. The optimized conversion efficiency can be achieved in the DSSC with ZnO/TiO2 assorted photoelectrode by using low series resistance of ZnO layer. INTRODUCTION Dye-sensitized solar cells (DSSCs) have been widely studied as a promising solar cell technology because of its low-cost and environmental-friendship [1, 2]. However, some critical issues such as the relatively low conversion efficiency and large-area integration are still block the practical application of DSSCs even though various technical solutions were proposed to solve the bottleneck problems [3-6]. It is well known that electron mobility of ZnO is much higher than that of TiO2, while the conduction band edge of both materials is approximate at the same level [3, 4]. Therefore ZnO was expected to be a good candidate as electron acceptor and transport material in DSSCs [5]. However, the reported photocurrent conversion efficiency of ZnO DSSCs is far less than that of TiO2 due to the poor dye absorption of ZnO [6]. In this paper, we proposed a novel ZnO/TiO2 assorted photoelectrode to improve the performance of DSSCs. The inserted ZnO layer between TiO2 and FTO is anticipated to enhance the electron transport efficiency to FTO due to the higher electron mobility than TiO2 and the blocking effect on the direct contact between FTO and electrolyte. The measured data demonstrated that the new ZnO/TiO2 assorted photoelectrode could effectively improve fill factor (FF) and the open circuit voltage Voc but the reduced series resistance of the inserted ZnO layer is needed to achieve the higher short circuit current. EXPERIMENT
In this study, ZnO and Ga-doped ZnO were fabricated by sol-gel process. For the ZnO, the 5g two
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