Copper(â…¡/â… ) Complexes Bearing Sulfur-coordinating Ligands As Redox Mediators In Dye-sensitized Solar Cells

In recent years,significant progress has been made for the application of copper（Ⅱ/Ⅰ）complexes as redox couples in dye-sensitized solar cells（DSCs）.The best power conversion efficiencies（PCE）based on copper electrolytes are 13.5%and 34.5%,respectively,under a standard sunlight intensity and indoor low light conditions.However,the majority of the research of copper redox mediators is based on nitrogen-coordinating liangds,such as phenanthroline and bipyridine and their derivatives.Fe w examples of copper（Ⅱ/Ⅰ）redox couples with sulfur-containing ligands have been reproted,but their photovoltaic performance is not satisfactory and needs to be further improved.In this thesis,we focus on the study of copper redox mediators bearing sulfur-coordinating liangds by by tuning the counterions and designing new ligand structures,with an aim to enhance the photovoltaic performance of DSCs using such redox systems.In chapter 2,copper complexes bearing sulfur-coordinating ligands,[Cu（N₂S₂）]^2+/+（N₂S₂=bis（2-pyridylmethyl）-1,2-ethanedithiol）),with tetrafluoroborate（[BF4]^–）and hexafluorophosphate（[PF6]^–）counterions were designed and synthesized,and were further applied as redox mediators in DSCs.Experimental studies have found that non-coordinating counterions have a significant effect on the molecular configuration of Cu（I）complexes.By changing the counterion from[BF₄]^–to[PF₆]^–,the solubility and diffusion coefficient of the Cu（I）complex were greatly improved.Therefore,DSCs based on the copper electrolyte containing[PF6]^–counterion exhibit higher short-circuit current and fill factor,which are closely related to the much improved charge collection efficiency and reduced series resistance.This leads to an impressive PCE of 10.3%under one sun illumination(100 m W cm^–2,AM 1.5G),which can rival that of the state-of-the-art copper bipyridine complex[Cu（tmby）₂]^2+/+（tmby=4,4’,6,6’-tetramethyl-2,2’-bipyridine）under identical conditions.Therefore,this study provides an effective method for developing more efficient r edox couples in DSCs.In chapter 3,new copper complexes bearing a pentadentate ligand,[Cu（N₂S₃）]^2+/+（N₂S₃=bis（2-（（pyridin-2-ylmethyl）thio）ethyl）sulfane）,were synthesized and used as redox couples in DSCs,in comparison with its pentadentate nitrogen-coordinating ligand counterpart([Cu（N₅）]^2+/+（N₅=N-benzyl-N,N’,N’-tris（6-methylpyridyl-2-methyl）ethylenediamine）.By changing the liangd structure,the redox potential of[Cu(N₂S₃)]^2+/+is increased to 0.74 V（vs.NHE）,which is 220 m V higher than that of[Cu（N₅）]^2+/+.Through the analysis of diffusion coefficient,transient absorption spectroscopy,and electrochemical impedance measurement,DSCs containing[Cu（N₂S₃）]^2+/+exhibit a higher charge collection efficiency and dye regeneration efficiency.Therefore,the photocurrent and photovoltage of the device with[Cu（N₂S₃）]^2+/+were both improved,leading to a higher PCE of 10.4%under one sun irradiation.