title: Metal-free tetrathienoacene sensitizers for high-performance dye-sensitized solar cells.
abstract: 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 × 10(4) 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 Å(2)), 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/cm(2), 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.
authors.affiliation: †Department of Materials Science and Engineering and the Materials Research Center, the Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Nanjia
authors.initials: N
authors.lastname: Zhou
authors.affiliation: ‡Department of Chemistry, National Central University, Chung-Li, Taiwan 32054, ROC.|∇Department of Chemistry, PSG College of Arts and Science, Coimbatore, India-641014.
authors.forename: Kumaresan
authors.initials: K
authors.lastname: Prabakaran
authors.affiliation: †Department of Materials Science and Engineering and the Materials Research Center, the Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Byunghong
authors.initials: B
authors.lastname: Lee
authors.affiliation: §Research Center for New Generation Photovoltaics, National Central University, Chung-Li, Taiwan 32054, ROC.
authors.forename: Sheng Hsiung
authors.initials: SH
authors.lastname: Chang
authors.affiliation: †Department of Materials Science and Engineering and the Materials Research Center, the Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Boris
authors.initials: B
authors.lastname: Harutyunyan
authors.affiliation: †Department of Materials Science and Engineering and the Materials Research Center, the Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Peijun
authors.initials: P
authors.lastname: Guo
authors.affiliation: ∥Department of Chemistry and the Materials Research Center, the Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Melanie R
authors.initials: MR
authors.lastname: Butler
authors.affiliation: ∥Department of Chemistry and the Materials Research Center, the Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Amod
authors.initials: A
authors.lastname: Timalsina
authors.affiliation: †Department of Materials Science and Engineering and the Materials Research Center, the Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Bedzyk
authors.affiliation: ∥Department of Chemistry and the Materials Research Center, the Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Ratner
authors.affiliation: ‡Department of Chemistry, National Central University, Chung-Li, Taiwan 32054, ROC.
authors.forename: Sureshraju
authors.initials: S
authors.lastname: Vegiraju
authors.affiliation: ‡Department of Chemistry, National Central University, Chung-Li, Taiwan 32054, ROC.
authors.forename: Shuehlin
authors.initials: S
authors.lastname: Yau
authors.affiliation: ‡Department of Chemistry, National Central University, Chung-Li, Taiwan 32054, ROC.|§Research Center for New Generation Photovoltaics, National Central University, Chung-Li, Taiwan 32054, ROC.
authors.forename: Chun-Guey
authors.initials: CG
authors.lastname: Wu
authors.affiliation: †Department of Materials Science and Engineering and the Materials Research Center, the Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Robert P H
authors.initials: RP
authors.lastname: Chang
authors.affiliation: ∥Department of Chemistry and the Materials Research Center, the Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.|⊥Polyera Corporation, 8045 Lamon Avenue, Skokie, Illinois 60077, United States.
authors.forename: Antonio
authors.initials: A
authors.lastname: Facchetti
authors.affiliation: ‡Department of Chemistry, National Central University, Chung-Li, Taiwan 32054, ROC.
authors.forename: Ming-Chou
authors.initials: MC
authors.lastname: Chen
authors.affiliation: ∥Department of Chemistry and the Materials Research Center, the Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Tobin J
authors.initials: TJ
authors.lastname: Marks