Tailoring of Energy Levels in D-Ï -A Organic Dyes via Fluorination of Acceptor Units for Efficient Dye-Sensitized Solar Cells

Min Woo Lee, Jae Yup Kim, Hae Jung Son, Jin Young Kim, Bongsoo Kim, Honggon Kim, Doh Kwon Lee, Kyungkon Kim, Duck Hyung Lee, Min Jae Ko

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A molecular design is presented for tailoring the energy levels in D-Ï ?-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 (V oc). 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.

Original languageEnglish
Article number7711
JournalScientific Reports
StatePublished - 16 Jan 2015

Bibliographical note

Funding Information:
All the authors acknowledge funding support from the Global Frontier R&D Program on Center for Multiscale Energy System (2012M3A6A7054856) and 2014 University-Institute cooperation program funded by the National Research Foundation under the Ministry of Science, ICT & Future Planning, Korea; This work was also supported from the KIST institutional programs (KIST Young Fellow Grant and 2E24821).


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