Theoretical Study Of Lindqvist Type Hexamolybdates Organic Amine Derivatives As The Sensitizer Of Dye Sensitized Solar Cells

In recent years, the energy crisis and environmental pollution are the threats to humansurvival and social progress. Solar energy as clean and non-polluting energy reserves a lot ofattentions. One of effective ways to utilize solar energy is changing the solar energy intoelectricity. Dye sensitized solar cells (DSSCs) have attracted the attentions of manyresearchers due to their unique advantages. A lot of polyoxometalate (POM)-basedorganic-inorganic hybrid materials have been reported. The hybrid materials combine theadvantages of both POM and organic groups, and created a new superior properties, forexample, the absorption in the visible region. Thus, POM-based organic-inorganic hybridmaterials are the candidates to be the photosensitizer in DSSC.Here, a variety of Lindqvist type hexamolybdates organic-inorganic hybrid materials havebeen designed. To deepen the understanding between the structure and property, the densityfunctional theory (DFT) and time-dependent density functional theory (TDDFT) calculationswere performed on the designed systems. Using quantum chemistry methods，the geometry,electronic properties, UV-vis absorption spectra and transition characteristics of systems aresystematically studied. The research work is mainly divided into four parts as following:1. A series of POM-based organic-inorganic hybrids modified by naphthalene and perylenerings were designed. Their electronic structures, absorption spectra and electronic transitioncharacteristics were systematically studied on the basis of TD-DFT calculations. The HOMOsdelocalize over the organic groups and extend to the anchoring groups. The LUMOs localizeon the POM cluster far from the anchoring site which is benefit to the charge separation.According to the Coulomb attraction, CSE of systems may increases in the order of system2<systems3and5<systems4and6due to the different r. The excitation energies of systemsdecrease along with the increasing π-conjugated bridge length and delocalization. Systems4and6are better candidates than others as the dyes of DSSCs due to the broad and strongabsorption in the visable region together with the higher CSE and HJE.2. A series of POM-based organic-inorganic hybrid dyes modified by thiophene and itsderivatives were systematically investigated as photosensitizers in DSSCs by employing DFTand TDDFT calculations. Different bridge fragments (BFs) between the donor [Mo6O18(N-1-C10H6-2-CH3)]2-and the acceptor cyanoacrylic acid anchoring group have affect on theabsorption spectra. The long π conjugation broaden the absorption bands of the dyes. Ourresults show that the large π-spacer and long π-conjugation demonstrate great effects on thespectroscopic properties of the designed dyes. From system1to system6, the absorptionspectra are systematically broadened and red-shifted with increasing size of π-spacer and length of π-conjugation. There is no distinct difference in the LHE of systems1-6. System2with thieno[3,2-b]thiophene demonstrates the balance of desirable energetic andspectroscopic parameters and is expected to be a promising sensitizer in the DSSC field. Ourtheoretical studies are expected to provide valuable insights into the POM-basedorganic-inorganic hybrid dyes and shed light on the molecular design of novel POM-baseddyes for the optimization of DSSCs.3. The organic-inorganic hybrids containing two hexamolybdate clusters have beeninvestigated using TDDFT method. Their electron structure, absorption spectra, transitioncharacter and application in DSSC are systematically investigated. The results indicate thatthe HOMO energies of systems are under the VB of NiO. The HOMO are delocalizedpredominantly on the organic groups and the LUMO delocalized over Mo6cluster. SystemII4have strong and broad absorption band in500nm-900nm due to the introduction ofthienothiadiazole. Compared with System II4, the absorption spectra of system II5is furtherred shifted because of the introduction of thienothiadiazole and thiophene. System II1and II2have more negative hole injuction energy and regeration energy and benefit to the holeinjuction and dye regeneration.4. To obtain more reasonable frontier molecular orbital （FMO）energies of α-Kegginanion [PW12O40]3-, the influence of different density functional theory (DFT) functionals aresystematically investigated. Excepted LC-ωPBE, M06HF, LC-BLYP, HF and LC-BP86, thefunctionals we tested overestimate the bond length with mean unsigned error (MUE) valuesranging from0.02to0.03. All the functionals used show that the typical trend tooverestimate the FMO energy levels. The hybrid generalized gradient approximation (hGGA),such as B3P86(MUE0.465eV), perform better than others. The results of Na3PW12O40aremore reasonable than [PW12O40]3-because the errors brought by the negative charge werecompensated. B3P86with13%HF exchange offers the reasonable MUE (≈0.12eV) ofM3PW12O40, M4SiW12O40and M6P2W18O62(M=Na, K).