Novel Organic Dyes Featuring Spiro[dibenzo[3,4:6,7]cyclohepta[1,2-b]quinoxaline-10,9′-fluorene] (SDBQX) as a Rigid Moiety for Dye-Sensitized Solar Cells

Abstract

Three novel organic dyes coded as FHD4, FHD5, and FHD6 featuring spiro­[di­benzo­[3,4:6,7]­cyclo­hepta­[1,2-b]­quinoxaline-10,9′-fluorene] (SDBQX) moieties were developed for dye-sensitized solar cells (DSSCs). The fluorenyl moiety of SDBQX is perpendicular to the quinoxaline moiety, which is beneficial in inhibiting the H-aggregation in DSSCs. The band gap energies according to DFT calculations showed a good correlation with the transition energy calculated from the absorption spectra, which indicates that the DFT calculations would be an effective method to predict the absorption spectra range for FHD-type dyes. Broad spectral coverage and a high molar extinction were observed in the absorption spectrum of FHD4, which leads to the best power conversion efficiency that was obtained for the FHD4-based DSSC. Coadsorption of CDCA improved the power conversion efficiency slightly for FHD4-based DSSCs (from 4.61 to 4.69%) and FHD6-based DSSCs (from 3.59 to 3.69%). The coadsorption of CDCA decreased the dye loading amount of FHD5 significantly, while the power conversion efficiency increased significantly from 3.18 to 3.73%. Finally, we have developed SDBQX as a new architecture for developing efficient organic dyes for DSSC applications.

Aggregation‐Free Organic Dyes Featuring Spiro[dibenzo[3,4:6,7]cyclohepta[1,2‐b]quinoxaline‐10,9′‐fluorene] (SDBQX) for Dye‐Sensitized Solar Cells

“…Typically, the addition of CDCA would improve the power conversion efficiency because it could obstruct the dye aggregation on TiO 2 film . Similar effects were observed for FHD4 , FHD5 , and FHD6 in our previous work . However, after coadsorption with CDCA, lower efficiencies were observed for analogues FHD4‐1 , FHD4‐2 , and FHD4‐3 (4.17%, 5.08%, and 4.34%, respectively) featuring with long alkyl chains mainly due to the reduction of J sc values.…”

“…Based on the molecular exciton theory, dye aggregation would lead to a shift of absorption spectrum . As for FHD4 , an obvious bathochromic shift was observed for absorption spectrum on TiO 2 film compared with in solution, which suggested that the existence of J ‐aggregation for FHD4 molecules on the surface of TiO 2 . The absorption onsets of FHD4‐1 , FHD4‐2 , and FHD4‐3 in solutions and adsorbed on TiO 2 films had good consistency and no apparent shifts were observed.…”

“…In the solution absorption spectra, all of the three dyes exhibited two prominent peaks at around 410–430 and 490–550 nm. The intense absorption bands in short wavelength region could be assigned to the π–π* transition . The absorption peaks in long wavelength region corresponding to the intramolecular charge transfer (ICT) from the electron donor to the electron acceptor were observed at 531, 545, and 490 nm for FHD4‐1 , FHD4‐2 , and FHD4‐3 , respectively .…”

“…Dye aggregation is a common phenomenon especially for planar dyes and it is adverse for DSSC performance . We have reported a series of D–A–π–A organic dyes ( FHD4 , FHD5 , and FHD6 ) featuring with spiro[dibenzo[3,4:6,7]cyclohepta[1,2‐ b ]quinoxaline‐10,9′‐fluorene] ( SDBQX ) moiety to suppress dye aggregation in DSSCs considering about the fluorenyl moiety is perpendicular to the quinoxaline moiety of SDBQX and a 3D structure is realized . However, dye aggregation was still not be eliminated especially for FHD5 and FHD6 .…”

Low‐Cost, High‐Efficiency, and Efficiency Predictable Small Molecule Organic Dyes with Bis(4‐styryl)phenyl Amino Donor for Dye‐Sensitized Solar Cells

“…The LUMOs of FWD4 ∼ FWD6 located on their electron acceptors and the phenyl ring connected with the electron acceptors. As a result, The HOMOs and LUMOs of FWD5 and FWD6 exhibited a greater overlap compared with FWD4 , resulting in faster ICT for FWD5 and FWD6 and hence more efficient electron injection from the excited dyes into the semiconductor TiO 2 , which is beneficial to the photovoltaic performance of DSSCs …”