| In the existing photovoltaic technologies, dye-sensitized solar cells(DSSCs) have been rapid development. As its important vital part, the sensitizer largely impact on DSSCs performance and can be divided into two classes: metal complex dyes and metal-free organic dyes. Although, metal complex dyes hold the highest power conversion efficiency, the advantages of metal-free organic dyes such as higher structural modification flexibility, easily available raw materials and less environmental issues give it opportunity to compete with metal complex dyes.For this, five series and 19 metal-free organic dyes for DSSCs are designed, synthesized and confirmed by the standard spectroscopic methods. Their photophysical and electrochemical properties are systematically studied. The performances of the cells sensitized by these dyes are investigated. The relationship between the dye molecule structure and their photovoltaic performance are discussed.In the second chapter, as compare to the dyes(iso DPP2) based the isomeride of DPP(isodiketopyrrolopyrrole, iso DPP), DPP2 has a much wider and stronger spectral response along with a better structure planarity, which help it exhibits the highest power conversion efficiency of 6.74%. This efficiency reaches 96% of N719(7.02%) under the same condition. However, DPP1 also using DPP ring as π-bridge behaves unthinkable efficiency for 0.16% even lower than that of its isomeride dye iso DPP1(2.01%). The possible reason for this may be that the introduction of two thiophene units causing 1) a large red-shift of the absorption leaving a really poor absorption in the range of 400–500 nm; 2) a unmatched LUMO level; 3) serious π-π staking. It means that the DPP-based dye molecules should be well designed especially for the multiple thiophene based DPP dyes.In the third chapter, three types of DPP-based dyes(Type 1-3) with phenyl unit are designed to search a better linking way between the donor and DPP. By comparison with Type 2 and Type 3 dyes(the dyes with a phenyl unit between the donor and DPP), Type 1 dyes incorporating the donor directly to DPP core lead to a better electron communication between the donor and acceptor, allowing an efficient charge transfer process. Therefore, Type 1 dyes own better UV-vis spectrum and IPCE response, and stronger ability for inhibiting electron recombination. Moreover, in the same type, the dyes with 4,4’-bis(n-hexyloxy)triphenylamine as the donor display better UV performance and lower trend of aggregation than the dyes with N-hexylphenothiazine. Finally, in these six dyes, TPA1 achieves the best efficiency of 7.57% without CDCA and 8% with CDCA. The results reveal that the donors and linking way both significantly influence their photovoltaic performance.In the furth chapter, three DPP-based dyes(TPh, BPh and SPh) with different π-bridge length are designed and synthesized. The influence of π-bridge length on the photophysical and photovoltaic properties are systematically investigated. On one hand, along with increasing phenyl unit(TPh), the coplanarity of the conjugated skeleton is reduced, causing a blue-shifted of UV-vis absorption range but fewer tendencies to aggregate. On the other hand, employing only one phenyl unit, SPh behaves the strongest light-harvesting capacity and smallest molecule size with the highest dye loading. But SPh has serious aggregation, short electron lifetime and poor DSSCs performance. With a moderate π-bridge length, BPh exhibits relative matched energy level, better incident photon-to-current conversion efficiency spectra(IPCE) response. Finally, it shows the highest efficiency(6.62%) with CDCA. So, for these dyes, the π-bridge length is not the longer the better as well as the shorter the better.In the fifth chapter, three double D-A branched dyes with different linkages are synthesized. Among them, owing to the better light harvesting capacity, the dye with a para-position linkage(p DB) exhibited the highest short-circuit photocurrent densityand open-circuit photovoltage, leading to the best efficiency(6.14%). Under similar measuring conditions, the dyes with ortho(o DB) and meta-position(m DB) linkage delivered efficiencies of 5.25% and 5.85%, respectively. The result shows the position isomer of the linkage units influences the photophysical characteristics, dye loading on film and electron lifetime.In the sixth chapter, three linear skeleton of D-D-π-A dyes with dihydro-5H-dibenzo[b,f]azepine as the key donor are designed. Among them, the dye(DBA-OH) with a hydroxy group as an additional anchoring moiety exhibited a maximum molar extinction coefficient of 24,136 M-1cm-1 at λmax = 458 nm and the best photovoltaic performance with an efficiency of 4.88%. The dye(DBA-COOH) with a carboxy group as an additional anchoring moiety exhibited the lowest efficiency(4.52%) though it has a highest dye loading. The results show that the dye loading on the film and photovoltaic performance of the dyes were influenced by the additional anchoring units. |
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