Theoretical Design And Characterization Of D-A-π-AConfigurations Photosensitizer In Dye-sensitized Solar Cells

As the global energy crisis and environmental pollution more and more serious,to seek a new high efficiency and clean resource become an urgent problem in thecurrent scientific research field. Under this background, a series of solar cells werechurned out. As one of the most prospective candidate, dye-sensitized solar cells(DSSCs) have attracted extensive attention due to their abundant raw materials,simple preparation, low costs, plasticity and environmental friendly. As the criticalcomponent of DSSCs, the sensitizers have been studied by more and more theoreticalworkers through simulating the structure of the dye molecules and reliable theoreticalcalculation method to reveal the molecular nature of the microcosmic properties andprovide further theoretical guidance for experimental design and synthesis.Nowadays, D-A-π-A configuration for metal-free organic dyes were reported andreceived increasing attention by incorporating an electron withdrawing moietychromophore acting as subordinate acceptor into the common D-π-A structure. Theseadditional acceptor chromophores have been proved to exert a better chargedelocalization ability, red-shift the absorption band to the low energy region, reducereorganization energy and suppress charge recombination has been extensivelystudied by scientist from early on. This thesis mainly to experimental synthesis ofindoline and triphenylamine D-A-π-A configuration dyes (IQ2and TQ2) by usingdensity functional theory (DFT) and time-dependent density functional theory(TD-DFT) methods and natural bonding orbital (NBO) analysis and C-PCMpolarizable continuum model methods are systematically investigated. The maininnovative research work of this paper can be summarized as follows:(1) In the thesis, involving indoline and triphenylamine dyes (IQ2and TQ2) asthe basic frame, four D-A-π-A configuration dyes were designed by replacingthiophene the original configuration of π-bridge using furan and benzene. Theelectronic and optical properties of all organic dyes (including IQ2and TQ2),including light-harvesting efficiency, lifetime of excited state, dipole moment,injection driving force, exciton binding energy and the number of injected electrons inTiO2semiconductor conduction band as well as the second order perturbation energy between the dye molecules with I-/I-3of the parameters in close connection with theshort-circuit current density Jscas well as the open-circuit photovoltage Voc, werecalculated by DFT and TD-DFT theory and in accordance with experimental resultswhich could be used to screen and characterize the dyes’photoelectric performance;(2) The influence of different donor (indoline and triphenylamine) and π-bridge(phenyl, furan and thiophene) involved in series of dyes (IQ and TQ) with D-A-π-Aconfiguration has been theoretically explored by DFT and TD-DFT calculation, andthe corresponding achievement reveals that IQ2has better photoelectric propertiesowning to the contribution of the indoline unit as donor and thiophene moiety as πconjugation bridge;(3) Based on the screened IQ2, three new dye molecules (IQS1, IQS2and IQS3)were designed by taking the place of the original C and S atoms on the extra electronwithdrawing group quinoxaline as well as π-bridge of the D-A-π-A configuration dyesusing N and Se atoms. The theoretical results revealed that compared with dye IQ2,our designed dyes IQS2and IQS3display much better light harvesting properties andlonger first excited lifetime, and this would facilitate the future experimental studiesto design and synthesize new efficient organic sensitizer.