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Tailoring of energy levels in D-π-A organic dyes via fluorination of acceptor units for efficient dye-sensitized solar cells.

Lee MW, Kim JY, Son HJ, Kim JY, Kim B, Kim H, Lee DK, Kim K, Lee DH, Ko MJ - Sci Rep (2015)

Bottom Line: As the number of incorporated fluorine atoms increases, the LUMO energy level of the organic dye is gradually lowered due to the electron-withdrawing effect of fluorine, which ultimately results in a gradual reduction of the HOMO-LUMO energy gap and an improvement in the spectral response.Systematic investigation of the effects of incorporating fluorine on the photovoltaic properties of DSSCs reveals an upshift in the conduction-band potential of the TiO2 electrode during impedance analysis; however, the incorporation of fluorine also results in an increased electron recombination rate, leading to a decrease in the open-circuit voltage (Voc).Despite this limitation, the conversion efficiency is gradually enhanced as the number of incorporated fluorine atoms is increased, which is attributed to the highly improved spectral response and photocurrent.

View Article: PubMed Central - PubMed

Affiliation: 1] Photo-Electronic Hybrids Research Center, Korea Institute of Science and Technology, Seoul, 136-791, Korea [2] Department of Chemistry, Sogang University, Seoul, 121-742, Korea.

ABSTRACT
A molecular design is presented for tailoring the energy levels in D-π-A organic dyes through fluorination of their acceptor units, which is aimed at achieving efficient dye-sensitized solar cells (DSSCs). This is achieved by exploiting the chemical structure of common D-π-A organic dyes and incorporating one or two fluorine atoms at the ortho-positions of the cyanoacetic acid as additional acceptor units. As the number of incorporated fluorine atoms increases, the LUMO energy level of the organic dye is gradually lowered due to the electron-withdrawing effect of fluorine, which ultimately results in a gradual reduction of the HOMO-LUMO energy gap and an improvement in the spectral response. Systematic investigation of the effects of incorporating fluorine on the photovoltaic properties of DSSCs reveals an upshift in the conduction-band potential of the TiO2 electrode during impedance analysis; however, the incorporation of fluorine also results in an increased electron recombination rate, leading to a decrease in the open-circuit voltage (Voc). Despite this limitation, the conversion efficiency is gradually enhanced as the number of incorporated fluorine atoms is increased, which is attributed to the highly improved spectral response and photocurrent.

No MeSH data available.


Photovoltaic performance of DSSCs employing an M series dye.(a) IPCE spectra. (b) Photocurrent–voltage (J–V) characteristics (light intensity: 100 mW/cm2, AM 1.5 G filter).
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f4: Photovoltaic performance of DSSCs employing an M series dye.(a) IPCE spectra. (b) Photocurrent–voltage (J–V) characteristics (light intensity: 100 mW/cm2, AM 1.5 G filter).

Mentions: Figure 4a shows the incident photon-to-current conversion efficiency (IPCE) for DSSCs employing the M series dyes as a function of the incident wavelength, which reveals that all three dyes exhibit a high maximum IPCE of 70–80%. The IPCE spectra also exhibit a similar trend to the UV-vis spectra, in that the IPCE spectrum is gradually extended as the number of incorporated fluorine atoms is increased due to the accompanying decrease in E0-0. The onset wavelength became longer in the order of M5 < M6 < M7; i.e., onset was at about 660, 710, and 750 nm for M5, M6 and M7, respectively. This data provides clear evidence that the reduction in the HOMO-LUMO energy gap that is created by the incorporation of fluorine as an additional acceptor unit can effectively improve the spectral response and photocurrent of DSSCs. This trend also influenced the photocurrent–voltage (J–V) characteristics, as shown in Fig. 4b and listed in Table 2, with the short-circuit photocurrent (Jsc) being gradually increased from 9.99 mA/cm2 with M5 to 11.78 and 14.20 mA/cm2 with M6 and M7, respectively. This increase in Jsc is mainly attributed to the extended wavelength range of light absorption that was confirmed by the IPCE spectra. In contrast, the open-circuit voltage (Voc) decreased as the number of incorporated fluorine atoms was increased; and since the magnitude of the increase in Jsc was greater than the decrease in Voc, the conversion efficiency was subsequently enhanced in the order of M5 < M6 < M7 (6.13, 6.46 and 7.12% for M5, M6, and M7, respectively).


Tailoring of energy levels in D-π-A organic dyes via fluorination of acceptor units for efficient dye-sensitized solar cells.

Lee MW, Kim JY, Son HJ, Kim JY, Kim B, Kim H, Lee DK, Kim K, Lee DH, Ko MJ - Sci Rep (2015)

Photovoltaic performance of DSSCs employing an M series dye.(a) IPCE spectra. (b) Photocurrent–voltage (J–V) characteristics (light intensity: 100 mW/cm2, AM 1.5 G filter).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4296309&req=5

f4: Photovoltaic performance of DSSCs employing an M series dye.(a) IPCE spectra. (b) Photocurrent–voltage (J–V) characteristics (light intensity: 100 mW/cm2, AM 1.5 G filter).
Mentions: Figure 4a shows the incident photon-to-current conversion efficiency (IPCE) for DSSCs employing the M series dyes as a function of the incident wavelength, which reveals that all three dyes exhibit a high maximum IPCE of 70–80%. The IPCE spectra also exhibit a similar trend to the UV-vis spectra, in that the IPCE spectrum is gradually extended as the number of incorporated fluorine atoms is increased due to the accompanying decrease in E0-0. The onset wavelength became longer in the order of M5 < M6 < M7; i.e., onset was at about 660, 710, and 750 nm for M5, M6 and M7, respectively. This data provides clear evidence that the reduction in the HOMO-LUMO energy gap that is created by the incorporation of fluorine as an additional acceptor unit can effectively improve the spectral response and photocurrent of DSSCs. This trend also influenced the photocurrent–voltage (J–V) characteristics, as shown in Fig. 4b and listed in Table 2, with the short-circuit photocurrent (Jsc) being gradually increased from 9.99 mA/cm2 with M5 to 11.78 and 14.20 mA/cm2 with M6 and M7, respectively. This increase in Jsc is mainly attributed to the extended wavelength range of light absorption that was confirmed by the IPCE spectra. In contrast, the open-circuit voltage (Voc) decreased as the number of incorporated fluorine atoms was increased; and since the magnitude of the increase in Jsc was greater than the decrease in Voc, the conversion efficiency was subsequently enhanced in the order of M5 < M6 < M7 (6.13, 6.46 and 7.12% for M5, M6, and M7, respectively).

Bottom Line: As the number of incorporated fluorine atoms increases, the LUMO energy level of the organic dye is gradually lowered due to the electron-withdrawing effect of fluorine, which ultimately results in a gradual reduction of the HOMO-LUMO energy gap and an improvement in the spectral response.Systematic investigation of the effects of incorporating fluorine on the photovoltaic properties of DSSCs reveals an upshift in the conduction-band potential of the TiO2 electrode during impedance analysis; however, the incorporation of fluorine also results in an increased electron recombination rate, leading to a decrease in the open-circuit voltage (Voc).Despite this limitation, the conversion efficiency is gradually enhanced as the number of incorporated fluorine atoms is increased, which is attributed to the highly improved spectral response and photocurrent.

View Article: PubMed Central - PubMed

Affiliation: 1] Photo-Electronic Hybrids Research Center, Korea Institute of Science and Technology, Seoul, 136-791, Korea [2] Department of Chemistry, Sogang University, Seoul, 121-742, Korea.

ABSTRACT
A molecular design is presented for tailoring the energy levels in D-π-A organic dyes through fluorination of their acceptor units, which is aimed at achieving efficient dye-sensitized solar cells (DSSCs). This is achieved by exploiting the chemical structure of common D-π-A organic dyes and incorporating one or two fluorine atoms at the ortho-positions of the cyanoacetic acid as additional acceptor units. As the number of incorporated fluorine atoms increases, the LUMO energy level of the organic dye is gradually lowered due to the electron-withdrawing effect of fluorine, which ultimately results in a gradual reduction of the HOMO-LUMO energy gap and an improvement in the spectral response. Systematic investigation of the effects of incorporating fluorine on the photovoltaic properties of DSSCs reveals an upshift in the conduction-band potential of the TiO2 electrode during impedance analysis; however, the incorporation of fluorine also results in an increased electron recombination rate, leading to a decrease in the open-circuit voltage (Voc). Despite this limitation, the conversion efficiency is gradually enhanced as the number of incorporated fluorine atoms is increased, which is attributed to the highly improved spectral response and photocurrent.

No MeSH data available.