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Benzimidazole-Branched Isomeric Dyes: Effect of Molecular Constitution on Photophysical, Electrochemical, and Photovoltaic Properties
journal contribution
posted on 2016-01-04, 21:35 authored by Govardhana Babu Bodedla, K. R. Justin Thomas, Miao-Syuan Fan, Kuo-Chuan HoThree
benzimidazole-based isomeric organic dyes possessing two triphenylamine
donors and a cyanoacrylic acid acceptor are prepared by stoichiometrically
controlled Stille or Suzuki–Miyaura coupling reaction which
predominantly occurs on the N-butyl side of benzimidazole
due to electronic preferences. Combined with the steric effect of
the N-butyl substituent, placement of the acceptor
segment at various nuclear positions of benzimidazole such as C2,
C4, and C7 led to remarkable variations in intramolecular charge transfer
absorption, electron injection efficiency, and charge recombination
kinetics. The substitution of acceptor on the C4 led to red-shifted
absorption, while that on C7 retarded the charge transfer due to twisting
in the structure caused by the butyl group. Because of the cross-conjugation
nature and poor electronic interaction between the donor and acceptor,
the dye containing triphenylamine units on C4 and C7 and the acceptor
unit on C2 showed the low oxidation potential. Thus, this dye possesses
favorable HOMO and LUMO energy levels to render efficient sensitizing
action in solar cells. Consequently, it results in high power conversion
efficiency (5.01%) in the series with high photocurrent density and
open circuit voltage. The high photocurrent generation by this dye
is reasoned to it exceptional charge collection efficiency as determined
from the electron impedance spectroscopy.
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Benzimidazole-Branched Isomeric Dyesdyetriphenylaminecyanoacrylic acid acceptorintramolecular charge transfer absorptionbenzimidazoleHOMOelectron impedance spectroscopycharge recombination kineticsphotocurrentelectron injection efficiencyC 4C 7LUMO energy levelsdonorcharge collection efficiencybutyl