서강대학교

초록/요약 도움말

Nowadays, finding and usages of practical renewable energy have been arise in global society because of depletion of fossil fuels and global warming. Current scientific trend have been on the seek for alternative energy sources that replace the expensive-oil-price era. In this respect, dye-sensitized solar cell has a significant potential to electrical usage of photon energy from sun, which have been considered as a one of the solution to the energy insufficiency, eco-friendly resource low cost equipment for generating electricity. The dye-sensitized solar cell is composed on mainly five components: 1) a photoanode, 2) a counterelectrode, 3) a sensitizer 4) a mesoporous semiconductor metal oxide film 5) a hole transporter/ electrolyte. Among them, we demonstrate a new design of sensitizer and their electrical behavior for better efficiency in dye sensitized solar cell. In first chapter, a general introduction to dye-sensitized solar cell, such as kinds of organic dye and their structure and the operating principles in dye sensitized solar cell. As a experimental issues, the chemicals, preparation of metal oxide film, data analysis and characterization will be carried out. It is notable work that the effect of fluorine substituted by π-conjugation in electron distribution dyes when our designed organic dye is working in dye-sensitized solar cell. Part I deal with that the normal to the surface (μz) can induce a shift in the conduction-band potential of the TiO2 electrode among the three dipole components along each axis. Dipole moment of benzene (M5), monofluorobenzene (M6), difluorobenzene (M7) and 2-(3-fluorophenyl)-3,6-dihexylthieno[3,2-b]thiophene (M8) is calculated by density functional theory (DFT) using the hybrid B3LYP functional with 6-31G* basis set. The conduction-band potential shift of the TiO2 electrode by electrochemical impedance spectroscopy (EIS) show that the chemical capacitance (Cμ) increased in the order of M5 < M8 < M6 < M7 at the same bias potential. It is worthy note that this positive dipole along the z-direction can induce an upshift in the conduction-band potential of the TiO2 electrode. It is observed that the IPCE spectrum was gradually extended, which result the decrease in E0-0 because the number of incorporated fluorine atoms increased. From this result, solar cell devices using the M7 organic dye exhibited a solar-to-electric conversion efficiency of 7.14%. In Part II, molecular engineering will be considered for surface passivation on metal oxide film. Four kinds of new organic dyes based on the triarlyamine-thieno[3,2-b]thiophene and triarlyamine-cyclopenta[1,2-b:5,4-b']dithiophene was synthesized with a distinguishable feature of this new π-conjugated spacer is thiophene and 3,4-ethylenedioxythiophene (EDOT). With application, it was observed that the interfacial charge transfer resistance (Rct) of M12 (EDOT) was increased more than M11 (thiophene) at the same bias potentials. We concluded that it come from the effect of surface passivation on nano crystalline TiO2 of the more bulky EDOT group more than thiophene group that impede the approach of cations and I3- ions in the electrolyte. A solar-to-electric conversion efficiency of 7.0% was achieved with M12, compared to 7.2% for N719 dye under similar experimental conditions. In Part III, change of π-bridges is studied for application in dye-sensitized solar cells (DSSCs), which were developed by incorporating electron-rich 4,4-dimethyl-4H-cyclopenta[1,2-b:5,4-b’]dithiophene with a benzene, thiophene and bithiophene moiety as π-bridges. Moreover, change of the HOMO-LUMO energy gaps and the amount of dye on TiO2 surface by π-bridges structure will be considered in this part. Due to the π-bridge of organic sensitizers in DSSCs, even 4,4-dimethyl-4H-cyclopenta[1,2-b:5,4-b’]dithiophene (M13) showed a narrow spectral response than other organic dyes, it leads to a greater short-circuit photocurrent (Jsc) by amount of dye. The impedance analysis revealed that the greater electron lifetime of the photoanode with M13 was attributed to the lower electron recombination rate caused by the blocking effect of compact layer. As a result, M13 showed much higher conversion efficiency (η = 7.15%) than other dyes under one sun condition (AM 1.5 G, 100 mW/cm2).