The Electrochemical And Photoelectrochemical Properties Of Nanostructured Metal Oxide Semiconducted Electrodes

The photoelectric conversion efficiency (IPCE) and energy conversion efficiency (η) of Dye Sensitized Solar Cells (DSSCs) has been the focus of research. The energy band of the semiconductor and the additives in liquid electrolyte solution have an important influence on the photoelectric-chemical properties of DSSCs, which has attracted more and more attention. The energy band of semiconductor and additives in liquid electrolyte were studied in this paper.(1) The band energetics of nanostructured electrodes heavily depend on solvents. The Efb and surface states of the nanostructured SrTiO3electrodes were investigated in a series of nonaqueous solvents in order to better understand the processes at the interface between nanostructured SrTiO3electrodes and electrolyte solution. The Efb, of SrTiO3electrodes in THF, Acetone, DMF, MeCN and EtOH were about-0.5V,-0.6V,-2.2V,-2.6V,-3.3V, and Ntrap were calculated to be9.76x1014,5.75x1015,2.995x1016,5.527x1016,1.567x1016cm-2, respectively. It is obvious that nonaqueous solvent have an important effect on the Efb, and trap state density of semconductor.(2) ZnO nanoparticles were synthesized by the solvothermal method. The nanoparticles and thin film were characterized by X-ray diffraction (XRD), Ultraviolet-visible spectrometry (UV) and Scanning electron microscope (SEM). The results indicated that ZnO nanoparticles have a high crystalline wurtzite structure with an average diameter of about35nm, and the film thickness is about4μm. The flat band edges (Efb) and the trap state densities of nanostructured ZnO electrodes in MeCN (containing0.2mol?L-1TBAP) are-2.0V and3.846x1016cm-2. After addition of Li+, Efb and Ntrap are about-0.15V and9.159x1013cm-2. The results show that the adsorption and embedded of Li+ions shifts Efb positively and decreases Ntrap. In addition, the Efb of ZnO electrode in THF, Acetone, DMF and EtOH were0.15V,-0.05V,-1.5V,-3.0V, Ntrap were calculated to be5.545x1013,5.628x1013,1.79x1016and5.58x1015cm-2respectively. The results demonstrate that Efb shifts positively as the coordination ability of solvents become strong, and the corresponding Ntrap decreases.(3) In this paper,4-tert-butyl benzoate tetramethyl ammonium was synthesized through the reaction between tertiary butyl benzoic acid and tetramethyl ammonium hydroxide. Then the structure of this sample was characterized by IR. At last, the photoelectric performance, band structure and surface states of TiO2thin film electrode in liquid electrolyte (containing4-tert-butyl benzoate tetramethyl ammonium) were investigated. The results showed that the maximum conversion efficiency was6.45%, as N3sensitized TiO2electrodes was immersed in ethanol (containing4-tert butyl benzoic acid tetramethyl ammonium) for20minutes. Electrochemical test indicated that Efb and Ntrap are-2.2V and5.683x1016cm-2without4-tert butyl benzoic acid tetramethyl ammonium. When TiO2electrodes were immersed in ethanol (containing4-tert butyl benzoic acid tetramethyl ammonium) for20minutes, Efb shifts to negative potential. Efb and Ntrap are calculated to be-2.8V and4.91x1016cm-2, respectively. This demonstrates that with the inductive effect, the change of conduction band position shifts Efb to negative and reduce the trap state density.