New Phenothiazine Organic Dyes With Anchoring Group Grafted At Different Position And DSSC Research

Dye-sensitized solar cells(DSSCs)have drawn great attention in recent couple of decades mainly due to their easy fabrication,high power conversion efficiency(PCE)and low cost.In DSSC device,the component of dye sensitizer plays roles of collecting sunlight and influencing charge generation/recombination,hence being a determinative element in terms of device performance.In this study,three organic dyes(CBPTZ-o,CBPTZ-m and CBPTZ-p)were designed and synthesized,in which Carbazole(Cz),phenothiazine(PTZ),and cyanoacrylic acid were used as donor,?-bridge,and anchoring acceptor,respectively.A hexyl chain was introduced in the N-position of PTZ spacer to suppress dye aggregation.The Cz was meta-linked to the PTZ bridge across a phenylene.Specifically,the linking position of the acceptor moiety relative to the?-bridge was varied as ortho-,meta-and para-for CBPTZ-o,CBPTZ-m and CBPTZ-p,respectively,aiming at studying the structure-property relationship as well as the impact on device performance.The main content includes three parts:(1)The synthesis and characterization of the three new dyes.Dyes CBPTZ-o,CBPTZ-m and CBPTZ-p were synthesized;and their molecular structures were confirmed by high-resolution mass spectrometry and nuclear magnetic resonance spectroscopy.Density functional theory was used to optimize the molecular structure and to predict the properties of the three dye molecules.Differences in photophysical and electrochemical properties were found and interpreted in detail.Specifically,the para-dye CBPTZ-p has the strongest light absorption capacity due to its best molecular orbital overlap.The excitation-spectrum study shows that the ICT excitons originate not only from direct ICT band transition but also from?-?~*energy transfer;(2)The investigation of DSSCs based on the three new-dyes.DSSC devices were prepared based on the three dyes.By measuring the photocurrent density-photovoltage curve and the monochromatic photoelectric conversion efficiency curve,the performance differences of the three devices were discussed and explained.The device based on dye CBPTZ-p achieved the highest PCE of 6.63%among the three new-dye based devices;(3)The study of the effect of molecular structure on properties of material and device.The molecular planarity,dye loading,time-resolved photoluminescence spectrum and electrochemical impedance spectroscopy of the three dyes were studied.The results show that the dye CBPTZ-p has the most planar molecular structure,the highest dye loading,the highest electron injection efficiency and the smallest charge recombination rate.