| The energy crisis and environmental pollution ha ve become the world’s two major problems that need to be solved urgently. The green and renewable energy produced from the solar system is one of the best choices. Owning to the easily and cheaply available raw materials, low cost manufacturing and moderate to good photovoltaic efficiencies, dye sensitized solar cells(DSSCs) have been drawn intensive interests. Sensitizer, including transition metal complexes and organic dyes, plays a vital role in the light harvesting, which provides electron and injects electron into the conduction band of the oxide semiconductor(e.g Ti O2) upon light excitation. To date, transition- metal complex sensitizers have reached PCE values exceeding 11%. However, the practical application of ruthenium-based dyes has become a critical problem owing to the limited availability and high cost of ruthenium metal and the extensive purification steps. Comparing to those transition- metal complex sensitizers, the organic dyes have the advantages of an easy purification procedure, convenient variation of molecular structures and cost effectiveness.Thus, three series of new metal- free organic dyes were designed and synthesized. To study the relationship of the structure and the photoelectric conversion efficiency, their photophysical, photoelectro-chemical and photovoltaic characteristics were investigated in detail. On the basis of these advantages, the research work was designed and divided into the following three parts:First, two new di-anchoring phenothiazine based A-D-π-D-A dyes were synthesized with N-octyl phenothiazine as the donor, cyanoacetic acid as the acceptor, 9,9-dihexylfluorene or 2,2’-(9,9-dihexylfluorene-2,7-diyl)dithiophene as core bridge linker, respectively. Their spectral, photovoltaic and electrochemical properties were investigated systematically. Compared with SP-1, the dual-channel anchorable organic dyes DP-1 and DP-2, containing two identical light- harvesting units, two anchoring groups and a core bridge linker in one molecule, have higher molar extinction coefficients and exhibit a red-shift of the absorption spectra which is favorable for the improvement of short-circuit current density. Consequently, DP-1based cell exhibits the highest overall power conversion efficiency of 5.87% with CDCA as co-adsorption material, which is 21% higher than that of the equivalent based counterpart. The results indicate that this type of A-D-π-D-A can improve the photovoltaic performance by tuning the suitable core bridge linker structure.Second, new asymmetry di-anchoring organic dyes(DP-3-D P-7) constituted triphenylamine, phenothiazine or carbazole as the electron donor units were designed and synthesized. The asymmetry di-anchoring organic dyes showed much higher HOMO energy and much lower LUMO energy, broader UV-Vis absorption range, better molar extinction coefficient, higher IPCE value and much higher short circuit current density than single D-A dye. The results are beneficial to the development of metal-free di-anchoring organic dyes with high performance.Third, we found a novel and simple way to synthesis 1,4-dihydropyrro[3,2-b]indole derivers. And, we also synthesized a series of new dyes based on 1,4-dihydropyrro[3,2-b]indole moiety as a donor unit for nano-crystalline Ti O2 solar cells. The nature of the dye structure plays a significant role on the absorption and electrochemical properties of the dyes. Among these dyes, IP-3 showed highest IPC E, Voc and Jsc values, which led to the power conversion efficiencies of 5.40%, which reached 75% of the N719-based DSSC. The molar extinction coefficient can be significantly improved by tuning the molecular architecture. With the aid of molecular modeling, molecular engineering, and synthesis in our laboratory are underway to develop a novel and more efficient 1,4-dihydropyrro[3,2-b]indole dye that have the potential to exhibit significant increase in DSSCs performance across a wider range of the solar spectrum. |
PDF Full Text Request