| With the comsumption up of traditional fossil energy, the humankind are eager to find new energy for replacement. Compared with other energy, the solar energy has many merits, such as endless, inexausitible and very clean with no pollution exsited, and it has been focused by scientists day by day. Among various utilization methods, dye-sensitized solar cells (DSSCs) have many advantages such as high efficiency, low cost, simple preparation, and so on. For an entire DSSCs, it is composed of many necessary components and sensitizers play decisive role in determining the DSSCs performance. So the search for highly efficient, stable and entirely practicable dyes become very important and has puzzled many scientists for a very long time. In this dissertation, we innovatively tailored carbazole units to the needed complex structures and introduced the modified carbazole units into the donor units or π-conjugated chains of the dyes. The photophysical, photochemical, computational analysis and the photovoltaic performance were studied subsequently.In chapter1, the background, the structure and the princibles of the DSSCs, and all the components of the cells were simply and definitely introduced. Then, the history and progress in high-efficiency sensitizers for DSSCs were reviewed. Based on that, the designing ways and the research content were presented.In chapter2, six new dyes containing three kinds of dibenzo heterocycles and one reference dye TPS were synthsized and their photoelectric properties and the corresponding DSSCs performance were systematically invetigated. The results showed that the dibenzo heterocycle unit distorted the dye molecule, thus sufficiently decreased the energy loss caused by fluorescene emission. Besides, the distorted structure suppressed the dye aggregation and charge recombination, thus desirably increased the open-circuit voltage. The dyes contaning dibenzothiophene or dibenzofuran units displayed lower efficiency than TPS due to the narrow absorption spectra; On the other hand, the absence of the attached alkyl chain accelerated the charge recombination rate, resulting their voltage in lower than the carbazole-contaning dyes. Under AM1.5solar light, TBS4device gave the highest efficiency of5.91%, much higher than the reference dye TPS (4.24%). When employing CH3CN as dye baths and using thicker TiO2films. TBS4device gave a short-circuit current density of13.89 mAcm"2, an open-circuit voltage of0.77V, an fill factor of0.66, corresponding to an overall efficiency of7.09%.In chapter3, in order to skrutiny whether the good planarity of the rigid donor is good for the DSSCs performance or not, five sensitizers based on rigid triarylamine donor and one reference dye based on triphenylamine donor were successfully synthesized and characterized. The study results suggested that the rigid donor contributed to the high molar extinction coefficients for the new dyes (5.0×104～8.1×104M-1cm-1for DIA1-DIA5,2.5×104M-1cm-1for TPS), as a result, high short-circuit current density for DIA2, DIA3and DIA5devices were observed. The new donor presented good rigidity and well-conjugated π plane received from the sophiscated designs, this would sufficiently delocalized the geneated positive charge upon photoexcitation, thus increase the charge-separated state and electron lifetime. The two ethyl units could suppress the dark current to some extent, thus it would improve the open-circuit voltage. This could be evidenced by the high open-circuit voltage for DIA2and DIA3sensitized devices. Among the six dyes, DIA3device exhibited the best performance with light-to-electricity conversion efficiency of6.50%, further optimization gave a short-circuit current density of14.05mA cm-2, an open-circuit voltage of0.75V, an fill factor of0.77, corresponding to an overall efficiency of8.09%under AM1.5solar light condition.In chapter4. four new dyes (DDC1-DDC4) containing dihydroindolo[2.3-b]carbazole as donor, thiophene, thieno[3,2-b]thiophene or benzothiadiazole as π-spacer, cyano acetic acid as acceptor and one reference dye CBZ constructuring carbazole as donor were successfully synthesized and characterized. The effects on the photophysical, photochemical properties and the photovoltaic performance, caused by the reinforced electron-donating ability of the donor and the expansion of the π system, were thoroughly investigated. The results showed that the highly effective conjugation for the new donor resulted in high molar extinction coefficients for the dyes DDC1-DDC4, this hugely improved the light-harvesting ability of the new dyes. Compared with traditional carbazole donor, it could be found that the new donor have several advantages, no matter from the short-circuit current or from the open-circuit voltage. Among these dyes. DDC4possessed broad absorption spectra, high electron injection efficiency and its sensitized DSSCs yielded a short-circuit current density of14.81mAcm-2, an open-circuit voltage of0.69V. an fill factor of0.69, corresponding to an overall efficiency of7.03%under AM1.5solar light condition. In order to examine the photo-stability and the thermo-stability of these dyes, absorption spectra on TiO2films with the variance of time or temperature were measured. The results suggested that the photo-stabilty order for some units are as follows: the new donor> carbazole. benzothiadiazole>thiophenen or thieno[3.2-b]thiophene. thieno[3,2-b]thiophene>thiophene. DDC4containing all the photo-stable units presented the best photo-stability. The thermo-stability measurements displayed that all the dyes were fairly thermo-stable, and the order of thermo-stabilty was the same as that of the photo-stability.In chapter5, three new dyes with elongated π-spacer and attached alkyl chains based on the dyes in chapter4were successfully synthesized. The effects on the photo-electric properties and photovoltaic performance, caused by the elongation of the π system and the introduction of alkyl chains, were scrutinized. The experiments results showed that the three dyes had high molar extinction coefficients (4.2～5.3M-1cm-1) and broad absorption spectra, which contributed to the good IPCE performance and the large short-circuit current density. To be mentioned, the absorption spectra of DDC8on TiO2films extended to near-IR light region while the onset wavelength of the IPCE for DDC8device was as long as850nm, this was seldomly reported for the pure organic dyes while the IPCE values were ensured to be on a normal level. In order to examine the films thickness difference on the photovoltaic performance, DSSCs under two conditions with different thickness of the scattering layer were fabricated and their performance were measured. The results showed that thicker scattering layer increased the short-circuit current density due to the increase of the dye adsorbed amount while the open-circuit voltage decreased because the dark currents were larged. Among the three dyes, DDC7displayed the best performance. Under the condition of thinner scattering layer, its device yielded an efficiency of6.53%, however, the efficiency was boomed to7.49%under thicker scattering layer condition. As to the photo-stability, it was found that all these dyes are fairly photo-stable with the percentage of the maximum absorbance variations in CT bands no more than3.1%. The BTD-incorporated dye DDC8displayed the best photo-stability. |
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