Theoretical Design And Screening Of Non-noble Metal Dye Sensitizers

Due to the energy shortage and environmental pollution issues,human beings have been developing non-polluting novel energy sources in recent years.Among them,solar energy gains extensive attentions because of its clean,environmentally friendly and other properties,and is considered as an ideal alternative to traditional fossil fuels.Dye-sensitized solar cells(DSSCs)become an important branch of solar energy applications due to its abundant,low cost,easy-toexcavate properties.Dye sensitizers have a crucial impact on the efficiency of the batteries because they are the key photo-to-electron conversion materials in DSSCs.Therefore,designing and screen of high-efficiency dye sensitizers is the key strategy to improve the efficiency of DSSCs.In this thesis,the optical properties,intramolecular electron transfer(IET)properties and interfacial electron injection properties of several kinds of dye sensitizers were investigated by using the density functional theory(DFT)and time-dependent DFT(TD-DFT)approach,based on relevant experimental findings.The research results of this thesis can not only explain the previous experimental results and elucidate the photoelectric conversion mechanisms,IET process and interfacial electron injection process,but also provide theoretical predictions for designing and screen of novel efficient dyes.Using thiophene derivatives applied in dye CYC-B11 as electron donor units together with various anchoring groups as electron acceptor units,we designed two series of cyclometalated Cu(I)-based dyes.Herein,we focus on the effects of different anchoring groups on molecular geometries,frontier molecular orbital levels,absorption spectra,intramolecular and interfacial electron transfer upon photo-excitation.Our results showed that,choosing cyanoacrylic acid and nitric acid as anchoring group can decrease the HOMO-LUMO gap,red-shift the spectral range,increase the effective electrons separation and transfer while choosing bipyridine-group as structural skeleton can promote light-harvesting capacity;choosing cyanoacrylic acid and nitric acid as anchoring group can transfer more electrons,longer distance with weaker orbital overlap,and the transferred electrons are mainly located on anchoring groups,which is benefical for electron injection while choosing carboxylic acid as anchoring group can transfer electrons faster;choosing phosphoric acid and carboxylic as anchoring group and phenanthroline-group as structural skeleton is beneficial for interfacial electron injection and dye regeneration.A series of dithiafulvene(DTF)derivative organic sensitizers with donor-?-acceptor(D-?-A)structure in DSSCs have been systematically investigated by DFT/TD-DFT method in tetrahydrofuran(THF)solution based on experimentally synthesized typical organic sensitizer DTF-C3.Our results showed that,introducing heteroaromatic groups in the ?-spacer stabilizes the LUMO levels(except EDOT group)and thus lowers the HOMO-LUMO energy gaps,leading to the redshifts of absorption spectra at the long wavelength region.The presence of thieno[3,2-b]thiophene,dithieno[3,2-b:2',3'-d]thiophene in ?-spacer,especially the combinations of these two groups,significantly improves the light-harvesting capability and maintains the excellent donor-to-acceptor intramolecular electron transfer properties of the sensitizers,facilitating the efficient charge separation and electron injection.Our results are expected to highlight the effect of functionalized ?-spacers on the photoelectronic properties of DTF-based metal-free organic sensitizers,and provide a new strategy and guidance for the screening of high-performance sensitizers for dye-sensitized solar cells.A series of Fe(II)-based dye sensitizers were designed by modifying electron donor units based on the iron–nitrogen–heterocyclic-carbene sensitizer 1 synthesized by Harlang recently.Then we focused on the effects of different electron donor units on orbital levels,absorption spectra,and intramolecular electron transfer.Our results showed that,thiophene can improve the absorption spectra efficiency,and the methyl mercaptan and benzene ring can improve the optical properties.Dye sensitizers 4 can transfer more electrons to the longest distance with the weakest orbital overlap between electron donor unit and electron acceptor unit.Overall,theses three series of sensitizer molecules we designed showed good photoelectric properties and electron transfer properties.Cu(I)-based sensitizers have wide absorption spectral coverage,and the quasi-tetrahedral structure of the center ensures that the recombination of photo-electrons is less likely to occur.The organic sensitizers have excellent spectral coverage and light-harvesting ability,and can transfer electrons fastest and farthest.Fe(II)-based sensitizers can transfer the most electrons upon photo-excitation and the spatial stereo-structure can hinder the electron recombination effectively.