Utilizing the Nb2O5 blocking layer to improve the power conversion efficiency of dye-sensitized solar cell under indoor light illumination

• Main Authors: Yen-Chiao Chen, 陳彥橋
• Other Authors: Chih-Ming Chen
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/58665991686015563282

碩士 === 國立中興大學 === 化學工程學系所 === 105 === In 1991, Michael Grätzel has invented the dye-sensitized solar cells (DSSCs) which the efficiency of the solar cells reaches 7 % under 1 sun condition. The DSSCs have many advantages of low cost, environment protection and easy fabrication. DSSCs are limited by the recombination reaction of the electrons from the fluorine-doped tin oxide (FTO) substrate back into the electrolyte and from the TiO2 to electrolyte. In order to suppress the electron recombination at the FTO/electrolyte interface, the Nb2O5 blocking layer which can prevent the electrolyte from direct contact with the FTO substrate is deposited on the FTO to improve the DSSCs performance. The FTO is dipped into NbCl5 ethanol solution for 30 s at room temperature to form Nb2O5 blocking layer after annealing. In transmission electron microscope (TEM) images, the thickness of Nb2O5 blocking layer is about 14 nm through three times dipping cycles. By atomic force microscope (AFM) and scanning electron microscope (SEM) analysis, the surface roughness of FTO decreases with increasing the dipping cycles because Nb2O5 layer forms onto FTO crystal defeat. To make sure the layer composition, the signal of Nb5+ is detected by X-ray photoelectron spectroscopy (XPS) result. Based on the analysis results of transmission line model and electrochemical impedance spectroscopy (EIS), the blocking layer can promote the DSSCs power conversion efficiency (PCE) by increasing the electron recombination resistance and reducing the series resistance. The suppression effect becomes obvious as increasing dipping cycles but a thick blocking layer can resist the illumination income and lower the short circuit current. In other word, the blocking layer has the optimum thickness to enhance the photovoltaic performance and plays a more important role in the indoor or low intensity lighting applications.