A Study Of Anthraquinone And Carbazole Dyes As Photosensitizers For DSSCs

Anthraquinone dyes and carbazole dyes with carboxylic acid as anchoring group aredesigned and synthesized as sensitizers for dye-sensitized solar cells (DSSCs). All compoundsobtained have been characterized by 1^H NMR and MS. The photophysical andphotoelectrocheimical properties and their performance on DSSCs are studied.The anthraquinone dyes (A1, A2 and A3) show very low performance when they areapplied in dye-sensitized solar cells (DSSCs), although they have broad and intenseabsorption spectra in the visible region (up to 800 nm). Transient absorption kinetics,fluorescence lifetime measurements and density functional theory (DFT) calculations areconducted to investigate the cause of such low DSSCs performance for these dyes. The resultsshow that the strong electron-withdrawing character of the two carbonyl groups (-C=O) onanthrquinone framework may lie behind the low performance by suppressing the efficientelectron injection from the dye to the conduction band of TiO₂.Carbazole dyes are used in dye-sensitized nanocrystalline solar cells. Cb4 with t-butyland thienyl groups has the best performance on DSSCs applications. The highest IPCE valuefor DSSCs based on Cb4 is 74% at 480 nm and the IPCE value is over 60% from 400 to 520nm. A solar energy-to-electricity conversion efficiency of 2.96% is obtained based on Cb4under simulated AM 1.5 (100mW cm^-2) irradiation with a short-circuit photocurrent density(J_sc) of 7.76 mA cm^-2, an open-circuit voltage (V_oc) of 592 mV and a fill factor (ff) of 0.64,which is up to 53% of N3 measured in the similar condition. Transient absorption kineticstestifies the process of electron injection into the conduction band of TiO₂. Density functionaltheory (DFT) calculations are conducted and prove that the position of the LUMO is close tothe anchoring groups (-COOH) which can enhance the orbital overlap with the titanium 3dorbitals and favour electron injection. Carbazole dyes have narrow absorption spectra in thevisible region, from 350 to 500 nm, resulting in the weak use of solar energy, which is animportant reason for the photoelectro peoperties of carbazole dyes inferior to N3.