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The Synthesis of Near-Infrared Sensitizers and Their Application in Dye-Sensitized Solar Cells

Author: LiuYiZuo
Tutor: LiJianBao
School: Tsinghua University
Course: Materials Science and Engineering
Keywords: DSC near-IR sensitization complex molecule porphyrinoidderivative photo-induced electron injection
CLC: TM914.4
Type: PhD thesis
Year: 2011
Downloads: 65
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Abstract


Dye-sensitized solar cells （DSC） that mimic the natural photosynthesis in plantsand bacteria have been widely regarded as the promising alternative to conventionalsilicon-based solar cells due to its low cost, simple fabrication, variety in color andshapes, and the stability in photovoltaic performances against light intensity fluctuation.In order to boost the large-scale marketing and application, the considerably lowerlight-to-electricity energy conversion efficiency compared to silicon solar cells needsfurther improvement, the fundamental way of which lies in enhanced utilization ofsunlight with longer wavelengths. Currently, most of the research efforts innear-infrared （near-IR） sensitization pay much attention to near-IR light absorption,whereas the profound topics of intra-molecular and interfacial electron transfer havebeen less studied. On the other hand, panchromatic response by co-sensitization orenergy relay either reduces dye loading amounts or requires high fluorescence quantumefficiencies, limiting the practicability and the ultimate performances. In this thesis, theconcept of complex molecules incorporating different chromophores was proposed soas to promote the light-harvesting and photo-responsive properties per unit TiO2area.Mechanistic studies on the influences of molecular structures and DSC compositions oncharge transfer, electron injection and energy conversion efficiencies have also beenperformed.Unsymmetrical azobenzene–phthalocyanine sensitizer TH2has been synthesizedfor the first time. By spectrum supplementation and electronic conjugation, lightabsorption as far as800nm has been realized. Steady-state fluorescence spectroscopywas employed to study the intra-molecular charge transfer mechanism. Correspondingadjustment of charge transfer directions has been carried out by protonating TH2withtrifluoroacetic acid, which has significantly enhanced the photo-responsive ability innear-IR region.A series of donor-substituted ethynyl-linked zinc porphyrin–free-base porphyrinhetero-dimers BMPA, BTBPA and DTBC, together with a non-donor-substitutedreference compound DTBP, have been synthesized. Effective electronic conjugationand excitonic coupling between porphyrin fragments have been induced by ethynylbridging, through which panchromatic light absorption has been realized. The effect of electron donating abilities on the photophysical, electrochemical and photovoltaicproperties has been systematically studied, and time-correlated single-photon-counting（TCSPC） fluorescence spectroscopy has been employed to characterize the in-situkinetic behaviors of the four sensitizers. The results were correlated to provide guidancefor near-IR sensitizer design.The widely ignored axial coordination of4-tert-butylpyridine （TBP）, which is acommon electrolyte additive, to the zinc porphyrin component has been proposed.Combined with TCSPC fluorescence spectroscopy, transient photovoltage spectroscopy,and other experimental and theoretical approaches, the effect of such coordination onthe kinetics–energetics compromise has been investigated. A non-TBP electrolytecontaining guanidinium thiocyanate （GuSCN） has been developed accordingly, withwhich the photovoltaic performances of the ethynyl-linked porphyrin hetero-dimershave exceeded those ever reported for porphyrin array sensitizers.

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CLC: > Industrial Technology > Electrotechnical > Independent power supply technology (direct power) > Photocell > Solar cells
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