Study On The Electron Transfer And Recombination Mechanism In Highly Efficient Dye-Sensitized Solar Cells

As a novel third generation solar cell, dye-sensitized solar cell (DSC) has beenrecognized as a promising photovoltaic technology due to its low material cost and hightheoretical conversion efficiency. At present, the photovoltaic conversion efficiency ismainly limited by the low charge collection efficiency in DSC device and resultant lowshort-circuit photocurrent density. It has been well documented that the chargecollection efficiency is mainly determined by the competition of the electron transferrate in the titanium oxide electrode and recombination reaction process across thephotoanode/electrolyte interface. Therefore, this thesis is closely focused on the electrontransport and interfacial charge transfer process in DSC device, as well as thecorresponding photovoltaic performance with ionic liquid electrolyte, single crystallinenanomaterial photoanode and nanoscale counter electrode.Dependence of the apparent viscosity, composition structure of the ionic liquidelectrolyte on the I3-ions diffusion coefficient, electron lifetime and electron diffusioncoefficients was systematically studied. Electrochemical impedance and electrontransfer dynamic results showed that, the anionic structure of a specific ionic liquidsignificantly influenced the diffusivity behavior of the electrolyte, and altered theelectron lifetime in the titanium oxide anode. While, the electron diffusion coefficient inthe titanium oxide electrode exhibited an obvious cationic-structure dominance, whichmight be caused by the specific adsorption of the cations on the titanium oxide surface.Single crystalline rutile nanorods decorated composite anode and high-energetic(001) faces-exposed single crystalline anatase nanoparticles electrode had been appliedto construct highly efficient DSC. Remarkable enhancements in the short-circuitphotocurrent density and photovoltaic conversion efficiency were observed with respectto the commercial Degussa P25nanoparticles electrode with a comparable surface area.The main reason for the photocurrent improvement of the former was attributed to thesignificant light scattering effect of the single crystalline nanorods together with thecharge collection superiority from the direct electron transport pathways of the lowdimensional anode structure. Nevertheless, the photocurrent enrichment of the later wasmainly ascribed to the notably enhanced dye-loading capacity of the anatase single crystals exposed with (001) facets. This result paves a novel way to construct highlyefficient DSC by utilization of such high-energetic facets single crystals.Low temperature chemical deposition method was used for the first time toprepare nanoscale Pt/TiO2composite counter electrode. Such composite counterelectrode displayed apparently enhanced electrochemical surface area and thuselectrocatalytic activity. The charge transfer resistance across the counterelectrode and electrolyte interface was reduced to25%in comparison with aconventional platinum electrode. For the first time, vertically-alignedsingle-walled carbon nanotubes arrays was applied in newly developedthiolate/disulfide redox shuttle (T2/T－) electrolyte and polysulfide electrolyte. Itwas noted from the electrochemical measurement results that such threedimensional structure of aligned carbon nanotubes array demonstrated distinctlyimproved electrocatalytic activity towards such iodine-free electrolytes thanconventional platinum counter electrode. Devices incorporated with suchcarbonaceous counter electrodes exhibited higher fill factor and short-circuitphotocurrent density in conjunction with T2/T－electrolyte. Therefore, suchaligned CNT arrays counter electrodes are believed to be a versatile candidatefor further improvement of the power conversion efficiency of other iodine-freeredox couple based DSC and polysulfide electrolyte based quantumdot-sensitized solar cells (QDSC).