Abstract
On the basis of thieno(3,2-b)thiophene and dithieno[3,2-b:2′,3′-d]thiophene (T2 and T3 moieties) as π-linker, the A, D and S series dyes were designed to investigate the effect of the introducing N+ as an “electron trap” into T2 and T3 on the properties of the dyes. The optimized structures, electronic and optical properties were investigated by the density functional theory (DFT) and time-dependent DFT (TD-DFT). The results show that the properties of the dyes are sensitive to the N+ position in π-linkers. D series dyes with electron-withdrawing units located near the donor have better properties than the corresponding A series with the electron-withdrawing units located near the acceptor. For A and D series, the N+ modified dye named T2N+1-d displays the largest red shift of the UV–vis absorption, the maximum integral values of the adsorption-wavelength curves over the visible light, the highest light harvesting efficiency (LHE, 0.996), and the strongest adsorption energy (−44.33 kcal/mol). T2N+1-d also has a large driving force of hole injection (ΔGinj, −0.74 eV), which results in a more efficient hole injection. Bearing a lengthier π-linker than T2N+1-d, the properties of T2N+1-s are further improved. T2N+1-d moiety or its increased conjugated derivatives may be a promising π-linker.
Highlights
Dye-sensitized solar cells (DSSCs) have attracted considerable attention, owing to their great potential of being environment-friendly and low-cost, ever since crucial contributions were made by Grätzel and co-workers in 1991 [1]
UV–vis absorption spectrum is an important characteristic for evaluating the properties of UV–vis absorption spectrum is an important characteristic for evaluating the properties of sensitizers for dye-sensitized solar cells (DSSCs)
The excited state properties were calculated at CAM-B3LYP/6-311G** level by the TD-density functional theory (DFT), which was widely applicable for predicting the properties of excited states [38,39]
Summary
Dye-sensitized solar cells (DSSCs) have attracted considerable attention, owing to their great potential of being environment-friendly and low-cost, ever since crucial contributions were made by Grätzel and co-workers in 1991 [1]. The development of tandem dye-sensitized solar cells (DSSCs) is limited by the low efficiency of p-type DSSCs [2,3]. In the design of a donor-acceptor dye, the π-linker group between the donor and the acceptor plays an important role, and has been widely studied [4,5,6,7]. Electron-rich thiophene (T1 moiety) was widely served as a π-linker for DSSCs due to its good performance for charge–transfer interaction and photovoltaic properties [8]. N atoms are often used to modify the dyes to improve the photovoltaic properties of DSSCs [10,11,12]. The amine salt groups with strong electron-withdrawing ability can be used as the “electron trap” to modify the dyes [15]. The suitable introduction of electron-withdrawing units into the π bridge as an “electron
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