Iron-doped titanium oxide photoelectrodes for dye-sensitized solar cells

• Main Authors: Han-Long Siao, 蕭翰隆
• Other Authors: Chien-Tsung Wang
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/15177758764351919607

碩士 === 國立雲林科技大學 === 化學工程與材料工程系碩士班 === 100 === Titanium oxide (TiO2) has been studied in many dye-sensitized solar cells(DSSC) applications. However, many dye sensitizers failed to achieve a high photo-to- electricity conversion efficiency on TiO2, owing to small difference between the excited states of the dye energy level(LUMO) and the conduction band(CB) of TiO2, resulted in decreases driving force of electron injection, limits the development of DSSC. Another problem limiting the solar cell performance is the charge recombination between injected electrons and dye molecules and electrolyte(I3－ ion), resulting in loss of photocurrent. In order to increase driving force of electron injection, shift the CB of TiO2 positively is a feasible strategy to improve the photo-to-electricity conversion efficiency, doping of metal atoms into semiconducting materials is a commonly adopted method. The doping metal atoms in TiO2 may shift the CB position positively, on the one hand, and, on the other hand, may acts as the traps of capture the electrons, injected electrons can be capture in the trap before recombination with dye and electrolyte, inhibit recombination of electron and hole, and enhanced charge- transfer efficiency. This study attempts to use iron-doped titanium oxide and used as the photoelectrode of dye-sensitized solar cells to improve the photo-to-electricity conversion efficiency. Iron doped TiO2 thin films with different doping levels were synthesized by the sol–gel spin coating method, structure and optical properties of thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), ultraviolet–visible spectroscopy (UV–vis), UV-vis diffuse reflectance spectroscopy (UV-DRS) and photoluminescence(PL). Photoelectrochemical behaviors were measured by a digital potentiostat. Doping of Fe in TiO2 resulted in a shift of absorption edge towards the visible region(red shift). The observed band gap energy decreased from 3.38 to 3.22 eV on increasing the Fe doping concentration upto Fe/Ti=0.01. From PL, Fe ion acts as the traps of capture the electrons, inhibit recombination of electron and hole, From Electrochemical impedance spectroscopy(EIS), low concentrations of iron doping contribute to the charge transfer. From Linear Sweep Voltammetry(LSV), Increasing the concentration of Fe ion gives rise to an important drop of VOC, shift the CB of TiO2 positively, enhanced driving force of electron injection. The photo-to-electricity conversion efficiency of dye-sensitized solar cells based on Fe/Ti=0.0005 (0.45 %) have a significantly increased resulting in a 28.5% improved conversion efficiency compared to TiO2(0.35 %). The improved performance is attributed to three factors: (1) enhanced driving force of electron injection, (2) enhanced charge- transfer efficiency, (3) increase amount of dye absorption.