Tsung-Yu Pan

National Chiao Tung University, Hsin-chu-hsien, Taiwan, Taiwan

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Publications (7)57.92 Total impact

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    ABSTRACT: New π-extended porphyrin dyes with long alkoxyl chains at the ortho positions of the meso-phenyls, and meta di-tert-butylphenyl-substituted porphyrins , and were synthesized for dye-sensitized solar cells, and their optical, electrochemical and photovoltaic properties were investigated and compared with those of and . The absorption spectra of showed a slight red shift of Soret bands and blue shift of Q bands as compared to the meta-substituted porphyrins due to the electron-donating effects of dioctyloxy substituents at the ortho-positions of the meso-phenyl rings. Replacement of the carboxyl with a cyanoacrylic acid as the anchoring group results in significant broadening and red shifts of the absorptions, which is due to the strong electronic coupling between the pull unit and the porphyrin ring facilitated by the C[triple bond, length as m-dash]C triple bond. The electrochemical studies and quantum-chemical calculations (DFT) indicated that the ortho alkoxy-substituted sensitizers exhibit lower oxidation potential, i.e. a higher HOMO energy level, and their HOMO-LUMO gaps are comparable to the meta-substituted analogues. The photovoltaic measurements confirmed that the ortho-octyloxy groups in the two meso-phenyls of and play a significant role in preventing dye aggregation thereby enhancing the corresponding short-circuit current density and open-circuit voltage. The power conversion efficiency (η) of is 8.04%, which is 11% higher than that of , whereas the efficiency of is 6.03%, which is 135% higher than that of . On the other hand, the poor performance of and is due to the floppy structural nature and limited molecular rigidity of the cyanoacrylic acid anchor.
    Physical Chemistry Chemical Physics 04/2013; · 3.83 Impact Factor
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    ABSTRACT: Co-sensitization of two or more dyes with complementary absorption spectra on a semiconductor film is an effective approach to enhance the performance of a dye-sensitized solar cell (DSSC). Porphyrin sensitizer YD2-oC8 showed outstanding photovoltaic performance co-sensitized with an organic dye to cover the entire visible spectral region, 400–700 nm. To promote the light-harvesting capability beyond 700 nm, a porphyrin dimer (YDD6) was synthesized for a co-sensitized system. We report a systematic approach for engineering of molecular co-sensitization of TiO2 films in a cocktail solution containing YD2-oC8, an organic dye (CD4) and YDD6 in a specific molar ratio to optimize the photovoltaic performance of the device. The resulting device showed panchromatic spectral features in the IPCE action spectrum in the region 400–700 nm attaining efficiencies of 75–80%; the spectrum is extended to the near-IR region attaining 40–45% in 700–800 nm region, giving JSC/mA cm−2 = 19.28, VOC/mV = 753, FF = 0.719, and η = 10.4% under standard AM 1.5 G one-sun irradiation. This performance is superior to what is obtained from the individual single-dye devices and the two-dye co-sensitized systems. The shifts of TiO2 potential upon dye uptake and the kinetics of charge recombination were examined through measurements of the charge extraction (CE) and intensity-modulated photovoltage spectroscopy (IMVS), respectively. Five co-sensitized systems were investigated to demonstrate that suppression of dye aggregation of YDD6 in the co-sensitized film is a key factor to further improve the device performance.
    Energy & Environmental Science 11/2012; 5(12):9843-9848. · 11.65 Impact Factor
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    ABSTRACT: A series of porphyrins bearing alkoxyl and/or alkyl chains were prepared to investigate the roles of alkoxyl/alkyl chains in the enhanced photovoltaic performance of the dyes. Based on the experimental results and the molecular simulations, we demonstrated that suitable long alkoxyl chains are capable of wrapping the porphyrin core, thus resulting in decreased dye aggregation, elevated excited states and LUMOs, and improved photovoltaic performance.
    Energy & Environmental Science 04/2012; 5(5):6933-6940. · 11.65 Impact Factor
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    ABSTRACT: Three alkoxy-wrapped push-pull porphyrins were designed and synthesized for dye-sensitized solar cell (DSSC) applications. Spectral, electrochemical, photovoltaic and electrochemical impedance spectroscopy properties of these porphyrin sensitizers were well investigated to provide evidence for the molecular design.
    Chemical Communications 03/2012; 48(36):4368-70. · 6.38 Impact Factor
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    ABSTRACT: Porphyrins bearing a polyaromatic or a heterocyclic group are prepared to study their fundamental and photovoltaic properties. Solar cells sensitized with a fluorene-modified porphyrin outperform other dyes in the series, reaching ~90% efficiency of N719 dye.
    Chemical Communications 03/2012; 48(36):4329-31. · 6.38 Impact Factor
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    ABSTRACT: We designed a stepwise approach for co-sensitization of a zinc porphyrin sensitizer (LD12) with a spirally configured organic dye (CD5) for dye-sensitized solar cells. The co-sensitized LD12 + CD5 device showed significantly enhanced VOC and JSC relative to its individual single-dye sensitized devices. Upon optimization, the device made of the LD12 + CD5 system yielded JSC/mA cm−2 = 16.7, VOC/V = 0.74, FF = 0.73 and η = 9.0%; this performance is superior to that of either individual device made from LD12 (η = 7.5%) and CD5 (η = 5.7%) under the same conditions of fabrication. To understand the effects of the potential shift and charge recombination on the cell performance, we measured charge-extraction (CE) and intensity-modulated photovoltage spectra (IMVS). Upon sensitization with each dye, the TiO2 potentials are similar, but co-sensitization causes the potential to shift down (cathodic shift). Charge recombination was significantly retarded for the co-sensitized system relative to each individual dye-sensitized system, to account for the enhanced VOC for the former relative to the latter. A test of stability indicates a systematic trend between the LD12 + CD5 and LD12 devices; the performance of the co-sensitized device degraded only 15% and remained stable during the period of 500–1000 h near 295 K.
    Energy & Environmental Science 03/2012; 5(4):6460-6464. · 11.65 Impact Factor
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    ABSTRACT: We designed highly efficient porphyrin sensitizers with two phenyl groups at meso-positions of the macrocycle bearing two ortho-substituted long alkoxyl chains for dye-sensitized solar cells; the ortho-substituted devices exhibit significantly enhanced photovoltaic performances with the best porphyrin, LD14, showing J(SC) = 19.167 mA cm(-2), V(OC) = 0.736 V, FF = 0.711, and overall power conversion efficiency η = 10.17%.
    Chemical Communications 06/2011; 47(31):8910-2. · 6.38 Impact Factor