Performance Optimization Of Dye-Sensitized Solar Cells By Surface Plasmon Resonance Of Au-Nanoparticles

Development of a clean,green and renewable energy to replace fossil fuels is one of the important research projects facing in the modern society and to be solved anxiously.It is also a great scientific and technological challenge worldwide.Solar energy is a abundant,widely obtainable and inexhaustible natural resource.The solar photovoltaic devices are the typical and important devices that convert solar energy to electrical energy.The dye-sensitized solar cells(DSSCs),in comparison with the high-cost conventional silicon solar cell,are currently attracting wide extensive scientific and technological research interests because of their relatively high photoelectric conversion efficiency(PCE),inexpensive materials and simple fabrication processes etc..To continue and further enhance the PCE and improve the performances of the DSSCs is the prerequisite for their commercial wide use.The photoanode is the core component in DSSCs,which plays a critical role in enhancing the PCE of the DSSCs.This doctorate dissertation focuses on enhancing the PCE and improving the performances of DSSCs by the surface plasmon resonance of Au nanoprticles and the novel architectures of the photoanodes.The main aspects of this dissertation are as follows:A series of TiO2-AuNRs@SiO2 composite photoanodes and DSSCs with differing amounts of AuNRs are prepared.The effects of different incorporation of AuNRs on DSSCs were studied.The study indicated that the introduction of AuNRs@SiO2 can enhance the range and strength of light absorption in photoanodes.The optimal properties were obtained in the 2.0wt%AuNRs@SiO2 doped DSSC,giving 23.0%higher than those of the conventional pure TiO2-based DSSC.The results show that the intense local electromagnetic fields produced by the local surface plamon resonance of AuNRs@SiO2 directly acts on the nearby dye molecules,which greatly enhances the absorption of light of dye molecules,thus effectively increasing the photogenerated charge and thereby improve the conversion efficiency.On the basis of above study,we continue to encapsulate a layer of TiO2 outside AuNRs@SiO2 to form a core-shell-shell structure(AuNRs@SiO2@TiO2).AuNRs@SiO2@TiO2 and graphene were both introduced into photoaodes and DSSCs.The influence of various hybrid architectures of the composite photoanodes on the performances of the DSSCs were explored.Studies revealed that the graphene doping obviously increased the dye absorbed in the photoanode and PCE of DSSCs.Incorporating of AuNRs@SiO2@TiO2 significantly increased light harvesting of the photoanode.The optimal properties were obtained in AuNRs@SiO2@TiO2 and graphene codoped DSSCs,getting the highest Js,of 16.26 mA/cm2 and PCE of 8.08%,giving 37.7%and 32.9%higher than those of the conventional TiO2-based DSSC,respectively.The performance of the DSSC were significantly enhanced due to the synergistic complementary superposition between the SPR of AuNRs@SiO2@TiO2 and the graphene,among which the encapsulated layer of TiO2 on AuNRs@SiO2 played an important role in increasing the specific surface area and dye adsorption capacity.Hierarchical TiO2 spheres(HTS)containing needle-like nanorods and decorated with Au nanoparticles are synthesized,forming the HTS-Au microspheres.A DSSC built up with a bilayer photoanode consisted of HTS-Au microsphere toplayer and a pure TiO2 nanocrystalline base layer was prepared.The effects of such HTS-Au microspheres on the performance of the photoanode and DSSCs are studied.Studies demonstrated that the introduction of the HTS-Au enhanced greatly the light absorption and light scattering of the photoanode,decreased the charge transfer resistance,increased electron lifetime,and thus improve significantly the performance of DSSCs.The optimal HTS-Au-based DSSC gets the highest Jsc of 14.56 mA/cm2 and PCE of 7.37%,The improvements in the properties of the optimal HTS-Au-based DSSC can be mainly attributed to these factors:the heightened light absorption and thus the photo-generated electrons due to the SPR from Au nanoparticles,the higher light scattering ability by the HTS-Au microspheres,and the possible faster electron transfer and longer electron lifetime associated with the unique needle-like nanorods microsphere morphologies.Graphene(G),TiO2 fusiform nanorods(TiO2NRs)adsorbed with Au nanoparticles(AuNPs)are prepared and blended as multifunctional materials into TiO2 nanocrystalline film to form a novel ternary(G-TiO2NRs-Au)composite photoanode in DSSCs.This ternary composite photoanode can take full advantages of the faster electron transport propersities and light scattering from TiO2NRs,SPR from the AuNPs and the high specific surface area and electron mobility from graphene,simultaneously.The results show that this ternary composite photoanode has successfully improved the the light absorption and scattering of the photoanode,decreased the charge transfer resistance,increased the carrier lifetime,and obtained PCE of 8.56%,which is 35.0%higher than that of conventional TiO2-based DSSC.This significant improvement can be attributed to the ternary composite complementary effects of multi-functions from the SPR of AuNPs,light scattering of TiO2 NRs,and the improved dye loading and fast electron transmission channel from graphene.A novel tri-layered TiO2 nanostructure as photoanode for DSSCs was fabricated and studied.In this novel photoanode,small TiO2 nanoparticles were used as the underlayer,the TiO2 nanorods were used as the intermediate layer and a large size TiO2 hierarchical microspheres were used as overlayer.For comparison,a monolayered TiO2 nanoparticles photoanode(T)and three double layered photoanodes which contains TiO2 nanoparticles as the underlayer and TiO2 nanorods as the overlayer(TR),TiO2 nanoparticles as the underlayer and TiO2 hierarchical microspheres as the overlayer(TS),and TiO2 nanorods as the underlayer and TiO2 hierarchical microspheres as the overlayer(RS)were also fabricated and studied.The novel tri-layered photoanode collects the advantages of efficient charge-collection,light harvesting,as well as high dyeloading capability.As a result,the PCE of DSSC based on the tri-layered TiO2 photoanode obtained the highest photovoltaic conversion efficiency(8.34%)compared with the DSSCs based on other photoanodes,which shows 34.0%higher than conventional DSSC.