2-Hexylthiophene-substituted Alizarin-based (D–π–A) Organic Dyes for Dye-sensitized Solar Cell Applications: Density Functional Theory and UV–Vis Studies

Abstract

This work reports density functional theory and time-dependent density functional theory calculations of the optimized geometries, electronic structures and optical properties of molecular dyes D1, D2, D3, D4, D5, and D6 formulated through substitution of 2-hexylthiophene to alizarin using the hybrid functional B3LYP and 6-31G (d,p) basis sets. The dyes are considered as potential pigments for dye-sensitized solar cells. For all dyes, HOMO/LUMO (Highest Occupied Molecular Orbital/Lowest Unoccupied Molecular Orbital) analysis results in positive outcomes upon electron injection to semiconductors and subsequent dye regeneration by the electrolyte. It is found that charge transfer is from the thiophene and unsubstituted ring of alizarin to the substituted ring of alizarin containing C=O and OH groups. The C=O groups are observed to be very important in strengthening the dyes as they are revealed to be the anchoring group bonding to the TiO2 semiconductor. Comparatively, dye D6 is observed to possess high absorption ability and electron injection power through a study of the light-harvesting efficiency and injection driving force (Δ Ginject). The estimated values of open-circuit voltage ( Voc) for the computed dyes are also presented. Decisively, all the considered dyes prove to be useful as potential photosensitizers in solar cells using a TiO2 semiconductor and [Formula: see text] coupling electrolyte.

Synthesis and photocurrent density–photovoltage (J–V) characterization of a novel alizarin derivative dye for dye-sensitized solar cell technology

“…The alizarin derivative dye HDD reported in this work displays the V oc of 0.65 V. This shows the drop of V oc value by 0.1 V as compared to the previous report of pure alizarin. The theoretical results reported previously for the alizarin derivative dye HDD had the V oc value of 0.734 V [36]. The value shows close correlation with the experimental value by just small difference of 0.084 V. Actually, one of the vital reason for the low efficiency of DSSCs is the low V oc output.…”

“…The future studies are also arguably to concentrate on improving V oc which will in turn improve the performance of the cell. Moreover, the studies on synthesis of other alizarin derivative dyes theoretically reported in our previous works are encouraged [4,36]. Fig.…”

“…Recently, a theoretical study on alizarin through substitution of its hydroxyl groups by conjugated molecules containing thiophene, benzene, and thieno[3,2-b]thiophene has been reported [35]. Not only that but also in our previous works we reported the theoretical study on substitution of alizarin molecule through its hydrogen atoms using 4-(benzo[c][1,2,5]thiadiazol-4-yl) benzoic acid, 2-hexylthiophene and carboxylic acid [4,36] where several dye molecules were argued to be useful in DSSCs application. Taking into consideration the several modification possibilities in alizarin through its hydroxyl groups, carbonyl groups and several attached hydrogen atoms, concentrating into studies on this molecule may result to a dye molecule which will go beyond pure alizarin in DSSC technology.…”

“…The few reported theoretical studies on derivative of alizarin have ended up with convincing outputs which arouse the mind set to think about its practical applicability hence a need for experimental studies on the same. Therefore this work reports the synthesis of one of the theoretically reported alizarin derivative dye [36] and its applicability in DSSCs technology. The reported dye molecule may be among the succession to the commercialization of DSSC which will reduce the crisis of power especially in rural areas of developing countries where the supply from national grid is still questionable.…”