Molecular Design of Anthracene-Bridged Metal-Free Organic Dyes for Efficient Dye-Sensitized Solar Cells

Abstract

A series of metal-free organic dyes bridged by anthracene-containing π-conjugations were designed and synthesized as new chromophores for the application of dye-sensitized solar cells (DSCs). Detailed investigations on the relationship between the dye structures, photophysical properties, electrochemical properties, and performances of DSCs are described. With the introduction of the anthracene moiety, together with a triple bond for the fine-tuning of molecular planar configurations and to broaden absorption spectra, the short-circuit photocurrent densities (J sc ) and open-circuit photovoltages (V oc ) of DSCs were improved to a large extent. The improvement of J sc is attributed to much broader absorption spectra of the dyes with the anthracene moiety. Electrochemical impedance spectroscopy (EIS) analysis reveals that the introduction of the anthracene moiety suppresses the charge recombination arising from electrons in TiO 2 films with I 3 ions in the electrolyte, thus improving V oc considerably. On the basis of optimized molecular structures and DSC test conditions, the dye TC501 shows a prominent solar energy conversion efficiency (η) up to 7.03% (J sc ) 12.96 mA • cm -2 , V OC ) 720 mV, ff ) 0.753) under simulated AM 1.5 irradiation (100 mW • cm -2 ).

Acene‐Modified Triphenylamine Dyes for Dye‐Sensitized Solar Cells: A Computational Study

“…For TPA-AC3, the calculated main emission band locates at 631 nm, which shows good agreement with experimental data, with a mean absolute deviation of 16 nm or 0.05 eV. [25] The calculated fluorescence emission spectra of TPA-AC1 to TPA-AC5 in CH 2 Cl 2 solutions are depicted in Figure 4, where the UV/Vis peak half-width at half height is 0.33 eV and the unit of fluorescence is cm À1 L mol À1 . As expected, the fluorescence maxima are red-shifted from 486 to 1013 nm from TPA-AC1 to TPA-AC5.…”

“…Especially for BHandH, the discrepancy between calculated and experimental results is within 36 nm or 0.2 eV. The long-range-corrected CAM-B3LYP provides the most stable and reliable results, predicting excitation energies very close to experimental data [25] with an absolute deviation of 27 nm or 0.15 eV, which is smaller than the generally accepted upper limit required for the design of new industrial dyes (0.2 eV). Therefore, on the basis of the agreement with experimental data, CAM-B3LYP is the functional of choice for the UV/Vis spectra calculation.…”

“…CAM-B3LYP PBE0 BHandH Experiment [25] The potential difference (the driving force) between the oxidized dyes and the I À /I 3 À redox couple determine the electron collection yields and the dye regeneration yields (F r ). [48] The oxidation potential of the dyes (corresponding to the ÀHOMO levels of dyes) must be more positive than the I À /I 3 À redox couple (4.60 eV vs. vacuum [22] ), thus ensuring enough driving force for a fast and efficient regeneration of the dye cation radical and avoiding the geminate charge recombination between oxidized dye sensitizers and photoinjected electrons in the nanocrystalline TiO 2 film.…”

“…Acenes are polycyclic aromatic hydrocarbons consisting of linearly fused benzene rings with big p conjugations, and acene compounds such as anthracene are expected to be beneficial to red-shift the absorption spectra. [23][24][25] Lin et al have reported a series of acene-modified zinc porphyrins (benzene to pentacene) and investigated their absorption spectra, electrochemical properties, and photovoltaic properties. For the performance of the DSSCs, the overall efficiencies first increase then decrease, and the introduction of anthracene shows the highest efficiency.…”

“…[24] Teng and coworkers have designed and synthesized a series of metal-free organic dyes bridged by anthracene-containing p conjugations, and they reported that with the introduction of the anthracene moiety, the J SC and V OC parameters of DSSCs were improved to a large extent. [25] In this work, we systematically broadened the metal-free TPA organic dye absorption bands with increasing sizes of acenes. We also studied the impact of acene units on the UV/ Vis and electrochemical properties of the TPA organic dyes, by employing high-level density functional theory (DFT), density functional tight-binding (DFTB), and time-dependent DFT (TDDFT) calculations.…”