Synthetic strategy of low-bandgap organic sensitizers and their photoelectron injection characteristics

Sukwon Kim, Hunbae Lim, Kwanghyun Kim, Chulhee Kim, Tae Yeon Kang, Min Jae Ko, Kyungkon Kim, Nam Gyu Park

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16 Scopus citations


Low-bandgap organic sensitizers are designed and synthesized for high photocurrent generation in dye-sensitized solar cell. Introduction of the π-conjugated benzothiadiazole (BTD) unit in K1, designated as K2, decreases the highest occupied molecular orbitallowest unoccupied molecular orbital (HOMOLUMO) gap energy from 2.63 to 2.10 eV, whereas the photovoltaic performance is not improved although the absorption threshold in incident photon-to-current conversion efficiency spectrum is extended from 650 nm to approximately 800 nm. Low photovoltaic performance is overcome by introduction of a phenylenevinylene moiety next to the BTD unit in K2, designated as K3 that shows similar HOMOLUMO gap energy and absorbance to those of K2. As a result, a K3-sensitized 5 μ m-thick TiO2 solar cell demonstrates photocurrent density of 12.24 mA/cm2, voltage of 0.549 V, and conversion efficiency of 3.8%, which is better than the conversion efficiency of 2.49% for K2 with photocurrent density of 8.13 mA/cm2and voltage of 0.470 V. According to nanosecond transient absorption spectroscopic study, photoexcited electron injection efficiency of K3 is found to be three times higher than that of K2, which is attributed to the higher photocurrent of K3.

Original languageEnglish
Article number5444983
Pages (from-to)1627-1634
Number of pages8
JournalIEEE Journal on Selected Topics in Quantum Electronics
Issue number6
StatePublished - Nov 2010

Bibliographical note

Funding Information:
Manuscript received October 31, 2009; revised December 23, 2009 and January 27, 2010; accepted January 30, 2010. Date of publication April 8, 2010; date of current version December 3, 2010. This work was supported in part by the Korea Institute of Science and Technology (KIST) internal Project, the Ministry of Commerce, Industry and Energy new and renewable energy R&D Project under Contract 2006-N-PV12-P-05 and the National Research Foundation of Korea Under Grant 2009-0092950 funded by the Korea Ministry of Education, Science and Technology. The work of N.-G. Park was also supported in part by KIST under the National Agenda Project.


  • Benzothiadiazole (BTD)
  • dye-sensitized solar cell (DSSC)
  • electron injection efficiency
  • highest occupied molecular orbitallowest unoccupied molecular orbital (HOMOLUMO) energy tuning
  • low-bandgap sensitizer


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