Theoretical Design Of Several New Sensitizers And Their Impact On The Performance Of Dye-Sensitized Solar Cell

In this paper, we studied the metal-free organic dyes firstly.A series of novel indoline dyes have been designed and investigated with the density functional theory(DFT) and time-dependent density functional theory(TD-DFT) by changing the position of auxiliary acceptor benzothiadiazole(BTD) in D-A-π-A organic sensitizers. In order to explore which position of auxiliary acceptor in D-A-π-A dye molecules is the most favorable for the photoelectric conversion efficiency, the electronic structures, photoinduced charge transfer character, lifetime of excited state, absorption spectral properties, injection driving force, vertical dipole moment, and NBO electron distribution analysis of the new design molecules and their parental molecule were analyzed in detail. Results showed that the performance of the dye-sensitized solar cell can be improved when the auxiliary acceptor is directly connected to the anchoring group. By introducing different heterocyclic rings, a series of novel zinc-porphyrin sensitized molecules with different intensity acceptors have been designed. Results indicated that the stronger of the electron-withdrawing ability is, the stronger the acceptor is. Moreover, the relationship between the different acceptors and the photoelectric conversion efficiency is also investigated. We hope the present results could provide theoretical guidance for designing more efficient photosensitizers. In addition, based on the triphenylamine dye sensitizer, rigid structure between the donor and π bridge were designed as well as further expand the conjugation extent of the dye molecules to explore their influence on the performance of dye-sensitized solar cells.1. Influence of position of auxiliary acceptor in D–A–π–A photosensitizes on photovoltaic performances of dye-sensitized solar cellsBy reading a large number of experimental papers, D-A-π-A dye molecules have been studied by many researchers. Based on these works performed by predecessors, one can find that the positions of additional electron-withdrawing unit in D-A-π-A configuration have three possibilities:(1) the place between the donor and π-bridge;(2) the middle of π-bridges; and(3) the space between π-bridge and anchoring group. In order to investigate the influence of the auxiliary acceptors’ position in D-A-π-A organic sensitizers on photovoltaic performances of dye-sensitized solar cells, a series of molecules were designed by changing the position of auxiliary acceptors in parental molecule and given a detailed comparison with the series of parameters affected dye-sensitized solar cells. Results showed that when the auxiliary acceptor locates in the space between π-bridge and anchoring group, the charge transfer efficiency, lifetime of the excited state, absorption spectra, vertical dipole moment of the sensitizers are superior to other positions. The excellent performance of these parameters is conductive to obtain a high open-circuit voltage and higher short-circuit current. When the auxiliary acceptor locates in the middle of the π-bridge, the perpendicular dipole moment and the number of electrons in the conduction band of dye molecules are smaller than those of the parental molecule, which may result in a lower Voc. This may be against the improvement of the dye-sensitized solar cell performance. We hope that the results of this study can provide a credible theoretical guidance for further molecular applications. 2. Theoretical study of YD2-o-C8-based derivatives as promising sensitizers for dye-sensitized solar cellsDye-sensitized solar cells(DSSCs) have become one of the hotspot in the field of energy due to its environmental friendly, easy to manufacture and low costs. However, the conversion efficiency of metal-free organic dyes is still lower than that of Ru complexes because of their narrow absorption spectra and poor photovoltaic properties. Besides, the widespread application of Ru complexes as dye sensitizer has been hampered by the limited supply and high cost of Ru metal. Therefore, the exploration of DSSCs using porphyrin dyes as an alternative to Ru complexes becomes very important from a practical point of view. In this paper, several heterocycles were selected according to their different structures and electron-withdrawing ability to modify stronger acceptors in YD2-o-C8. Results suggested that with the electron-withdrawing ability of the introduced heterocycle increasing, the HOMO-LUMO energy gap decreased, the absorption spectrum red shifted, the electron transfer ability improved, the strength of electronic coupling between the anchoring group and TiO2 semiconductor electronic enhanced. This study is helpful for further understand how the stronger acceptor affect the performance of DSSCs. We hope the present results can provide theoretical guidance for designing more efficient photosensitizes. 3. Theoretical study of the influence of rigid structure and the expansion of conjugation degree on the performance of triphenylamine-based sensitizers.In recent years, dye-sensitized solar cells(DSSCs) has attracted wide attention, a lot of researches have been concentrated on varying the conjugation degree of the donor part or the π-bridge section in D-π-A structure, as well as using the rigid structure to expand the coplanarity of the donor moiety or π-bridge portion, which can enhance the performance of dye-sensitized solar cell. In this work, a rigid structure was created between donor and π-bridge. Then the conjugation of the rigid structure was expanded to obtain a good DSSCs performance. By comparing the electronic structures, photoinduced charge transfer character and optical properties, our purpose is to obtain a good design method. The electronic spectral information and electronic structures of triphenylamine sensitizers are calculated using density functional theory(DFT) and time-dependent density functional theory(TD-DFT). Results indicated that the rigid structure makes the new designed molecule exhibit 34 nm red-shifted. With the further expansion of conjugation, bathochromic-shift is more and more obvious and the maximum redshift nearly 120 nm. In addition, the oscillator strengths of the new designed dye molecules are improved. Therefore, the introduction of a rigid structure between the donor and the π-bridge together with the expansion of the conjugation is a feasible strategy to improve the performance of dye-sensitized solar cells.