Metal-Free Tetrathienoacene Sensitizers for High-Performance Dye-Sensitized Solar Cells

Nanjia Zhou, Kumaresan Prabakaran, Byunghong Lee, Sheng Hsiung Chang, Boris Harutyunyan, Peijun Guo, Melanie R. Butler, Amod Timalsina, Michael J. Bedzyk, Mark A. Ratner, Sureshraju Vegiraju, Shuehlin Yau, Chun Guey Wu, Robert P.H. Chang, Antonio Facchetti, Ming Chou Chen, Tobin J. Marks

Research output: Contribution to journalArticlepeer-review

208 Scopus citations


A new series of metal-free organic chromophores (TPA-TTAR-A (1), TPA-T-TTAR-A (2), TPA-TTAR-T-A (3), and TPA-T-TTAR-T-A (4)) are synthesized for application in dye-sensitized solar cells (DSSC) based on a donor-π-bridge-acceptor (D-π-A) design. Here a simple triphenylamine (TPA) moiety serves as the electron donor, a cyanoacrylic acid as the electron acceptor and anchoring group, and a novel tetrathienoacene (TTA) as the π-bridge unit. Because of the extensively conjugated TTA π-bridge, these dyes exhibit high extinction coefficients (4.5-5.2 × 104 M-1 cm-1). By strategically inserting a thiophene spacer on the donor or acceptor side of the molecules, the electronic structures of these TTA-based dyes can be readily tuned. Furthermore, addition of a thiophene spacer has a significant influence on the dye orientation and self-assembly modality on TiO2 surfaces. The insertion of a thiophene between the π-bridge and the cyanoacrylic acid anchoring group in TPA-TTAR-T-A (dye 3) promotes more vertical dye orientation and denser packing on TiO2 (molecular footprint = 79 Å2), thus enabling optimal dye loading. Using dye 3, a DSSC power conversion efficiency (PCE) of 10.1% with Voc = 0.833 V, Jsc = 16.5 mA/cm2, and FF = 70.0% is achieved, among the highest reported to date for metal-free organic DSSC sensitizers using an I-/I3- redox shuttle. Photophysical measurements on dye-grafted TiO2 films reveal that the additional thiophene unit in dye 3 enhances the electron injection efficiency, in agreement with the high quantum efficiency. (Graph Presented)

Original languageEnglish
Pages (from-to)4414-4423
Number of pages10
JournalJournal of the American Chemical Society
Issue number13
StatePublished - 8 Apr 2015


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