Theoretical Characterization And Design Of D-A Type Squaraine-based NIR Dyes In Dye Sensitized Solar Cells

As the energy shortage and environmental pollution are becoming more and more serious,there is an increasing demand for clean and renewable energy.Dye sensitized solar cells（DSSC）have attract researchers’great attention,owing to their advantages of low cost,flexibility,environmentally friendly and high efficiency.Currently,its recorded efficiency is still fall behind the inorganic silicon solar cells,and we still need to accelerate the developing process for large scale commercial application.Notably,as the important component of the device,the dye is directly related to the final efficiency,participating in the process of light harvesting,interfacial charge separation,and charge injection and so on.So a large number of works have been done based on the optimization of the dyes’structure.However,the experimental works of synthesizing high performance dyes face the conundrum of resources and time-consuming problems.Moreover,the quantum chemical calculations are believed to be reasonable and suitable solution to it.In this paper,we investigated the relationship between the dyes’structure and the performance of the cell in a molecular level by performing density functional methods.Based on it,we designed and characterized a series of potential organic dyes,with the aim to provide theoretical foundation for screen of high performance dye in experiments.This paper mainly includes two parts of work:1.At present,although the efficiency of DSSCs based on cis-squaraine（HSQ）is not very large,HSQ is considered as promising near-infrared chromophores on account of its superior spectral absorption,compared with trans-squaraine（SQ）.By applying DFT and TD-DFT methods,we comprehensively analyzed the photoelectric properties of dyes with different dithiophene groups,associated with light-capturing ability,interfacial charge separation,electron injection and electron recombination and so on.The results show that HSQ-DTS possesses better charge separation ability and can effectively inhibit electron recombination to inject more electrons.In order to improve the DSSC’s efficiency,we theoretically designed another six dyes and made an evaluation.Fortunately,dye 3 not only exhibited comparable performance with HSQ-DTS,but also show a maximum short-circuit current of 31.60 mAcm^-2,which made it the most promising candidate.We hope this paper would provide beneficial references for experimental synthesis.2.Considering that the final efficiency of DSSCs’device will be significantly affected by tiny modifications in dye’s structure.We took a theoretical investigation and revealed that the reason why the efficiency of the experimental dye（SQ-DTS）and the original dye（SQ）vary considerably.Besides,the impacts induced by BTZ group on the performance of SQ-DTS were also analyzed.A series of parameters related to the short-circuit current（）and the open-circuit voltage(（1）were calculated using density functional theory（DFT）and time-dependent DFT（TD-DFT）methods.The results show that the light-capturing ability is remarkably enhanced,and the extended distance from the cationic dye to the semiconductor surface can effectively suppress electron recombination,due to the addition of DTS and BTZ groups.Hence,considering the superior performance of SQ-DTS-BTZ,we theoretically designed dyes 1-3 with different substituents.Through comprehensive comparison,dye 1shows better performance and is expected to further improve the efficiency of DSSCs.