Li-Na Yang

Molecular engineering of quinoxaline dyes toward more efficient sensitizers for dye-sensitized solar cells

D–A–π–A-featured organic dyes incorporating diphenylquinoxaline unit (such as IQ4) have shown great potential in anti-aggregation and broadening spectral response in the field of dye-sensitized solar cells (DSSCs). The crucial restriction for quinoxaline-based cell to attain higher efficiency is the relatively low photocurrent density (JSC). In the present work, three novel push–pull dyes only differing in electron donors, have been designed based on the IQ4 backbone, in order to further improve the light-harvesting capability of quinoxaline dyes and to examine the donor influence on dye performance. Theoretical analysis of the factors correlated with the JSC and open-circuit photovoltage (VOC) demonstrate that, relative to the parent IQ4 dye, the NIQ4 dye bearing the elegant N-annulated perylene donor shows a good performance in light harvesting, electron injection, and dye regeneration, indicating an increased JSC potential for the related cell. Furthermore, despite possessing a smaller vertical dipole moment, the improved blocking effect of NIQ4 not only prevents unfavorable self-aggregation, but also effectively inhibits the parasitic back-recombination. Therefore, the NIQ4 is proposed to be a potential dye in DSSC applications.

Theoretical design of porphyrazine derivatives as promising sensitizers for dye-sensitized solar cells

Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations have been carried out on the electronic structure and optical properties of a set of heterocycle-fused zinc porphyrazine (ZnPz) derivatives, aiming at screening efficient sensitizers for dye-sensitized solar cells (DSSCs). Our results show that the absorption spectra of the designed dyes shift to longer wavelengths and the light harvesting efficiencies are much higher than isolated ZnPz. Moreover, the designed dyes have larger contributions of the anchoring group to the lowest unoccupied molecular orbitals (LUMOs) compared with the currently best sensitizer YD2-o-C8, indicating enhanced electron injection ability from the sensitizer to the semi-conductor. Furthermore, the designed dyes exhibit good performance in terms of the charge transfer characteristics, the driving force of electron injection and dye regeneration, and the excited-state lifetime. Overall, the designed dyes, especially indigo blue fused ZnPz and acridine fused ZnPz, are revealed to be promising sensitizers for high-efficiency DSSCs.

Iodinated AlIII‐Based Phthalocyanines are Promising Sensitizers for Dye‐Sensitized Solar Cells; A Theoretical Comparison Between ZnII, MgII, and AlIII‐Based Phthalocyanine Sensitizers

To design efficient dyes for dye-sensitized solar cells (DSSCs), using a Zn-coordinated phthalocyanine (TT7) as the prototype, a series of phthalocyanine dyes (Pcs) with different metal ions and peripheral/axial groups have been investigated by means of density functional theory (DFT) and time-dependent DFT (TDDFT) methods. Computational results show that the iodinated Al-based dye with a peripheral amino group (Al-I-NH2-Pc) exhibits the largest redshift in the maximum absorbance (λ(max)). In addition, Al-based dyes have appropriate energy-level arrangements of frontier orbitals to keep excellent balance between electron injection and regeneration of oxidized dyes. Further, it has been found that the intermolecular π-staking interaction in Al-I-Pc molecules is weaker than the other metal-based Pcs, which may effectively reduce dye aggregation on the semi-conductor surface. All these results suggest iodinated Al-based Pcs (Al-I-Pcs) to be potentially promising sensitizers in DSSCs.

How does the silicon element perform in JD-dyes: a theoretical investigation

Inspired by the successful utilization of silicon cores axially coordinated by trihexylsiloxy groups in naphthalo/phthalocyanine dyes, using ullazine-based dye JD21 as the prototype, we designed three novel silicon-core JD analogues in this work. Based on the theoretical analysis on the four dyes and the corresponding dye/(TiO2)38 complexes, the Y2 dye with the dithienosilole (DTS) conjugation unit is recognized as a star molecule for its impressive performance in various aspects, including remarkable light-harvesting capability, large driving force for dye regeneration (ΔGreg = 0.65 eV), excellent balance between the rates of electron injection (kinj = 1.48 × 1012 s−1) and electron–hole recombination (krec = 1.68 × 1010 s−1), and high stability for the adsorbed system Y2/(TiO2)38. It is thus proposed as a promising candidate for application in dye-sensitized solar cells (DSCs).

A promising candidate with D-A-A-A architecture as an efficient sensitizer for dye-sensitized solar cells.

A series of metal-free organic dyes with electron-rich (D) and electron-deficient units (A) as π linkers have been studied theoretically by means of density functional theory (DFT) and time-dependent DFT calculations to explore the effects of π spacers on the optical and electronic properties of triphenylamine dyes. The results show that Dye 1 with a structure of D-A-A-A is superior to the typical C218 dye in various key aspects, including the maximum absorption (λmax =511 nm), the charge-transfer characteristics (D/Δq/t is 5.49 Å/0.818 e(-) /4.41 Å), the driving force for charge-carrier injection (ΔGinject =1.35 eV)/dye regeneration (ΔGregen =0.27 eV), and the lifetime of the first excited state (τ=3.1 ns). It is thus proposed to be a promising candidate in dye-sensitized solar cell applications.

Theoretical study on the adsorption mechanism of iodine molecule on platinum surface in dye-sensitized solar cells

Abstract By means of density functional theory calculations, the adsorption process of I2 at Pt (111) surface in dye-sensitized solar cells (DSSCs) has been investigated. The obtained adsorption energies and stable structures depending on the adsorption sites of the Pt surface are in good agreement with experimental values. Our results show that the dissociative chemisorption and the non-dissociative chemisorption are competitive for the adsorption of I2 on the Pt surface, and the dissociative pathway is more favored in energy. This study is expected to enrich the understanding on the origin of the excellent heterogeneous catalytic performance of Pt for triiodide reduction and the complex iodine chemistry in DSSCs. Understanding of this adsorption mechanism is helpful for rational screening for redox couple and the Pt-free alternative counter electrode materials.