title: Rational Molecular Engineering of Indoline-Based D-A-π-A Organic Sensitizers for Long-Wavelength-Responsive Dye-Sensitized Solar Cells.
abstract: Indoline-based D-A-π-A organic sensitizers are promising candidates for highly efficient and long-term stable dye-sensitized solar cells (DSSCs). In order to further broaden the spectral response of the known indoline dye WS-2, we rationally engineer the molecular structure through enhancing the electron donor and extending the π-bridge, resulting in two novel indoline-based D-A-π-A organic sensitizers WS-92 and WS-95. By replacing the 4-methylphenyl group on the indoline donor of WS-2 with a more electron-rich carbazole unit, the intramolecular charge transfer (ICT) absorption band of dye WS-92 is slightly red-shifted from 550 nm (WS-2) to 554 nm (WS-92). In comparison, the incorporation of a larger π-bridge of cyclopentadithiophene (CPDT) unit in dye WS-95 not only greatly bathochromatically tunes the absorption band to 574 nm but also largely enhances the molar extinction coefficients (ε), thus dramatically improving the light-harvesting capability. Under the standard global AM 1.5 solar light condition, the photovoltaic performances of both organic dyes have been evaluated in DSSCs on the basis of the iodide/triiodide electrolyte without any coadsorbent or cosensitizer. The DSSCs based on WS-95 display better device performance with power conversion efficiency (η) of 7.69%. The additional coadsorbent in the dye bath of WS-95 does not improve the photovoltaic performance, indicative of its negligible dye aggregation, which can be rationalized by the grafted dioctyl chains on the CPDT unit. The cosensitization of WS-95 with a short absorption wavelength dye S2 enhances the IPCE and improves the η to 9.18%. Our results indicate that extending the π-spacer is more rational than enhancing the electron donor in terms of broadening the spectral response of indoline-based D-A-π-A organic sensitizers.
authors.affiliation: Shanghai Key Laboratory of Functional Materials Chemistry, Key Laboratory for Advanced Materials and Institute of Fine Chemicals, Collaborative Innovation Center for Coal Based Energy (i-CCE), East China University of Science and Technology , Shanghai 200237, P. R. China.
authors.forename: Weiwei
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Shanghai Key Laboratory of Functional Materials Chemistry, Key Laboratory for Advanced Materials and Institute of Fine Chemicals, Collaborative Innovation Center for Coal Based Energy (i-CCE), East China University of Science and Technology , Shanghai 200237, P. R. China.
authors.forename: Yongzhen
authors.initials: Y
authors.lastname: Wu
authors.affiliation: Shanghai Key Laboratory of Functional Materials Chemistry, Key Laboratory for Advanced Materials and Institute of Fine Chemicals, Collaborative Innovation Center for Coal Based Energy (i-CCE), East China University of Science and Technology , Shanghai 200237, P. R. China.
authors.forename: Haibo
authors.initials: H
authors.lastname: Zhu
authors.affiliation: Shanghai Key Laboratory of Functional Materials Chemistry, Key Laboratory for Advanced Materials and Institute of Fine Chemicals, Collaborative Innovation Center for Coal Based Energy (i-CCE), East China University of Science and Technology , Shanghai 200237, P. R. China.
authors.forename: Qipeng
authors.initials: Q
authors.lastname: Chai
authors.affiliation: Shanghai Key Laboratory of Functional Materials Chemistry, Key Laboratory for Advanced Materials and Institute of Fine Chemicals, Collaborative Innovation Center for Coal Based Energy (i-CCE), East China University of Science and Technology , Shanghai 200237, P. R. China.
authors.forename: Jingchuan
authors.initials: J
authors.lastname: Liu
authors.affiliation: Shanghai Key Laboratory of Functional Materials Chemistry, Key Laboratory for Advanced Materials and Institute of Fine Chemicals, Collaborative Innovation Center for Coal Based Energy (i-CCE), East China University of Science and Technology , Shanghai 200237, P. R. China.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.affiliation: Shanghai Key Laboratory of Functional Materials Chemistry, Key Laboratory for Advanced Materials and Institute of Fine Chemicals, Collaborative Innovation Center for Coal Based Energy (i-CCE), East China University of Science and Technology , Shanghai 200237, P. R. China.
authors.forename: Xiongrong
authors.initials: X
authors.lastname: Song
authors.affiliation: Shanghai Key Laboratory of Functional Materials Chemistry, Key Laboratory for Advanced Materials and Institute of Fine Chemicals, Collaborative Innovation Center for Coal Based Energy (i-CCE), East China University of Science and Technology , Shanghai 200237, P. R. China.
authors.forename: Wei-Hong
authors.initials: WH
authors.lastname: Zhu
keywords: co-sensitization; indoline dyes; light harvesting; photovoltaics; solar cells