Synthesis And Application Of Anti-aggregation Dyes For Dye-Sensitized Solar Cells

Dye-sensitized solar cells（DSSCs）are regarded as one of most potential solar cells.It is one of the most direct and effective methods to improve the performance of dye-sensitized solar cells by optimizing the structure of sensitizers.Molecular aggregation is a nagative factor which limiting the improvement of efficiency.In this thesis,in order to supress dye aggregation,a series of novel sensitizers were designed from the perspective of donor andπ-spacer.The photophysical and electrochemical properties of the dyes were measured,The light-harvesting performance,dye regeneration and electron injection of thermodynamic possibility were systematically analyzed by UV-vis absorption spectra and cyclic voltammetry.By means of quantum chemistry computation,the optimalized configuration and electron distribution were obtained,the anti-aggregation ability of dyes was discussed.By analyzing the influence of the photoelectric performance after addition of adsorbent,the relationship between the structure and the anti-aggregation property was studied.In the first chapter,the effects of alkyl chain（including length,type and connection position）,large steric group,twisted configuration and spiral structure on dye aggregation are reviewed successively.According to these literatures,it is found that the appropriate degree oextending the alkyl chain,increasing the steric hindrance and introducing non-planar structure are all benefical to improve the anti-aggregation ability of the dye.However,it can also be found that these improvements also bring some disadvantages,such as reduced planarity,decreased adsorption,reduced light harvesting ability.This paper is based on these deficiencies,and a series of sensitizers are designed.In the second chapter,the effect of the auxiliary donor encapsulated insulated molecular wire（EIMW）was inverstigated on anti-aggregation ability.Two efficient dye-sensitized solar cells were fabricated by two novel D–D–π–A phenothiazine-based organic dyes（PH2 and PH3）with EIMW as an auxiliary donor.Compared with PH1 without EIMW,the light-harvesing range and the molar extinction coefficients of PH2 and PH3 are increased.The photoelectric conversion efficiencies of DSSCs based on PH1-3 decrease in order of（7.08%）>PH3（6.51%）>PH1（5.64%）.When chenodeoxycholic acid（CDCA）added,the efficiencies of PH1-3 are increased by 40%,11%and 20%,respectively.Therefore,the high photoelectric conversion efficiencies of devices based on PH2 and PH3 can be rationalized by the introduction of cyclic alkyl chain,which inhibits intermolecular aggregation.PH2 and PH3 show significantly higher open circuit voltage than PH1,which may be attributed to the EIMW obstructs the electron recombination and reduces dark current on the surface of TiO₂.The results suggest that EIMW as auxiliary donor not only inhibits dye aggregation,but also weakens charge recombination.In third chapter,the effect ofπ-spacer on dye aggregation ability is studied.In view of the fact that the EIMW as auxiliary donor can reduce dye aggregation,a novel sensitizer IBT1 with EIMW asπ-spacer was designed.At the same time,2’,7’-bis（hexyloxy）spiro[cyclopenta[2,1-b:3,4-b’]dithiophene-4,9’-fluorene]（SPDF）was first designed to obtain dye IBT2.Compared with the reference dye IBT3 with3,3’-dihexyl-2,2’-bithiophene（DHBT）as anti-aggregationπ-bridge,IBT1 and IBT2 show a wider absorption region and higher molar extinction coefficients.The density functional theory（DFT）calculations show that the conjugated skeletons of IBT1 and IBT2 are more planarity than IBT1.Meanwhile,IBT1 with EIMW and IBT2 with SPDF asπ-bridges can both suppress intermolecular aggregation more efficiently than IBT3.Theπ-bridge SPDF shows the strongest anti-aggregation ability due to the rigid‘T’configuration among these dyes.Meanwhile,theπ-bridge of EIMW shows better anti-aggregation ability than DHBT because of its larger steric hindrance.In order to enhance the performance,the co-sensitization strategy is applied.Finally,the new devices exhibit high efficiencies of 7.85%（IBT1+IBT3）and 7.64%（IBT2+IBT3）,respectively,which are comparable to that of N719（7.85%）.The results demonstrate that the dyes with EIMW and SPDF as anti-aggregationπ-bridges are promising candidates for efficient DSSCs and dye aggregation can be effectively inhibited by structural engineering ofπ-spacer.In fourth Chapter,four novel sensitizers DTE1-4 were designed,synthesized and applied to DSSCs successfully.N,N-bis（4-（hexyloxy）phenyl）aminopurine（TPPA）was employed as a donor and 2’,7’-bis（2,6-bis（hexyloxy）phenyl）spiro[cyclopenta[2,1-b:3,4-b’]dithiophene-4,9’-fluorene]（HSPDF）asπ-spacer were first applied to DSSCs.Compared with DTE1,novel dye DTE2 with TPPA as a donor shows obvious blue-shifted at maximum absorption wavelength,which may be attributed to the large dihedral angle between the donor andπ-bridge.However,DTE3 and DTE4 with HSPDF asπ-spacer present a significantly red-shifted at maximum absorption wavelength.The anti-aggregation properities of the four sensitizers are studied by deprotonation experiments,DFT calculations and co-adsorption experiments.The results indicate that TPPA and theπ-bridge HSPDF can inhibit the intermolecular interaction effectively.The introduction of TPPA as donor will greatly increase the dihedral angle between the donor andπ-spacer.Therefore,DTE2 and DTE4 show twist configurations,which lead to inhibition of dye aggregation.While HSPDF used as aπbridge also show sinificant inhibitory effect due to the cross-shaped configuration.Finally,the device based on IBT3 achieved a PCE of 7.23%,which is nearly 93%relative to N719-based standard cell.The results suggest that HSPDF is a potential anti-aggregationπ-spacer for high-efficiency DSSCs.In conclusion,we designed a series of novel anti-aggregation structures and dyes.A lot of optimistic results are obtained by testing the properties of the dyes and devices,some of which reached or even exceeded the level of N719 under the same conditions.The results of anti-aggregation experiments show that the dyes containing EIMW/SPDF/HSPDF structures have anti-aggregation performance and can improve the photoelectric properties of the devices significantly.In addition,EIMW and HSPDF also can suppress dark current and obtain higher open-circuit voltage.These findings will contribute to the design of sensitizers and the development of dye-sensitized solar cells in the future.