Molecular engineering of organic sensitizers for solar cell applications.

  • Kim S
  • Lee J
  • Kang S
 et al. 
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Abstract

Novel organic sensitizers comprising donor, electron-conducting, and anchoring groups were engineered at molecular level and synthesized. The functionalized unsymmetrical organic sensitizers {3-{5-[N,N-bis(9,9-dimethylfluorene-2-yl)phenyl]-thiophene-2-yl}-2-cyano-acrylic} acid {(JK-1)} and {3-{5'-[N,N-bis(9,9-dimethylfluorene-2-yl)phenyl]-2,2'-bisthiophene-5-yl}-2-cyano-acrylic} acid {(JK-2),} upon anchoring onto {TiO2} film, exhibit unprecedented incident photon to current conversion efficiency of 91%. The photovoltaic data using an electrolyte having composition of 0.6 M {M-methyl-N-butyl} imidiazolium iodide, 0.04 M iodine, 0.025 M {LiI,} 0.05 M guanidinium thiocyanate, and 0.28 M tert-butylpyridine in a 15/85 (v/v) mixture of valeronitrile and acetonitrile revealed a short circuit photocurrent density of 14.0 +/- 0.2 {mA/cm2,} an open circuit voltage of 753 +/- 10 {mV,} and a fill factor of 0.76 +/- 0.02, corresponding to an overall conversion efficiency of 8.01% under standard {AM} 1.5 sunlight. {DFT/TDDFT} calculations have been performed on the two organic sensitizers to gain insight into their structural, electronic, and optical properties. Our results show that the cyanoacrylic acid groups are essentially coplanar with respect to the thiophene units, reflecting the strong conjugation across the thiophene-cyanoacrylic groups. Molecular orbitals analysis confirmed the experimental assignment of redox potentials, while {TDDFT} calculations allowed assignment of the visible absorption bands.

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Authors

  • Sanghoon Kim

  • Jae K Lee

  • Sang O Kang

  • Jaejung Ko

  • J-H H Yum

  • Simona Fantacci

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