Abstract
The dye sensitized solar cells (DSSCs) have been extensively studied due to their low production cost and simple fabrication process. Dye co-sensitization broadens the absorption spectrum of the sensitizer; thus enhances light harvesting efficiency; and contributes to the improvement of the DSSCs overall efficiency. In this study we performed theoretical design of complex molecule (C45H32N2O4) through combination (esterification reaction) of the natural dye lawsone and synthetic metal free indoline dye D131. The excitation energies, vibration spectra, molecular structures, electronic absorption spectra and electron transitions in individual dyes and complex molecule were investigated using density functional theory (DFT) and time dependent density functional theory (TD-DFT) B3LYP5 methods, with 3-21G, 6-31G and 6-31G(d,p) basis sets. The UV-Vis absorption spectra of the individual dyes and their mixture in chloroform solution were measured using spectrophotometer. For the complex formation reaction, enthalpy, entropy and Gibbs free energy were calculated and the results indicated the reaction was endothermic and non-spontaneous. Electron density distribution of the frontier and adjacent molecular orbitals and energy levels alignment were used for analysis of the electronic spectra and mechanism of transitions. The results indicated that the designed complex molecule satisfied the requirements for good photosensitizer of DSSCs.
Highlights
Due to increase in the environmental pollution and limited resource of fossil fuel, the development of solar energy harvesting is considered as a promising technology to substitute the fossil fuel, eliminate environmental pollution and sustain development of human societies.dye sensitized solar cells (DSSCs) have attracted substantial attention, because of their environmental friendliness, low manufacturing cost, simple fabrication process and tunable aesthetic color, and due to their lower dependence on the angle of incident light and higher efficiency under low irradiance compared to traditional Si-based solar cells [1]-[7]
Indoline dye D131 is composed of 4-(2, 2 diphenylethenyl) phenyl) substituent acting as a donor and π conjugated to the indoline ring, cynoacrylic acid group as an acceptor [30] (Figure 1(b))
The formation of this bond is accompanied by detachment of the H1-atom from cynoacrylic acid group of indoline D131 dye and hydroxyl O1-H6 from lawsone dye to release water molecule
Summary
Due to increase in the environmental pollution and limited resource of fossil fuel, the development of solar energy harvesting is considered as a promising technology to substitute the fossil fuel, eliminate environmental pollution and sustain development of human societies.DSSCs have attracted substantial attention, because of their environmental friendliness, low manufacturing cost, simple fabrication process and tunable aesthetic color, and due to their lower dependence on the angle of incident light and higher efficiency under low irradiance compared to traditional Si-based solar cells [1]-[7]. Working electrode is made of thin layer of semiconducting materials such as titanium dioxide (TiO2), zinc oxide (ZnO), tin dioxide (SnO2) coated with dyes on top of FTO [8] [9]. Counter electrode is made of FTO with thin layer of platinum or carbon [10]. Electrolyte is placed between counter electrode and photoelectrode to mediate electrons [11]. Among of these components of DSSC, the sensitizer (dye) is a crucial element which plays a significant role in light capturing, electron injection and dye regeneration which impact on power conversion efficiency (PCE) as well as the stability of the devices
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