Copper (?/?) Complexes Bearing Pentadentate Ligands As Redox Mediators In Dye-sensitized Solar Cells

In recent years,significant progress has been made in dye-sensitized solar cells(DSCs)based on copper(?/?)complex electrolytes,achieving a power conversion efficiency(PCE)of over 34%under indoor light conditions.However,a key problem of such an electrolyte system is that Lewis base additives(such as 4-tert-butylpyridine,TBP)can destroy the commonly used copper complexes based on bidentate bipyridine and phenanthroline ligands.Therefore,design of new copper complexes is of great significance for DSCs to further improve the PCE and long-term stability.In this thesis,a new class of copper complexes[Cu(tpe)]^2+/+(tpe=N-benzyl-N,N?,N?-tris(pyridin-2-ylmethyl)ethylenediamine)and[Cu(tme)]^2+/+(tme=N-benzyl-N,N?,N?-tris(6-methylpyridin-2-ylmethyl)ethylenediamine)were used as redox couples of DSCs.Through the modification of the ligand structure,the redox potential of[Cu(tme)]^2+/+complex positively shifts 420 m V relative to that of[Cu(tpe)]^2+/+,resulting in a higher open-circuit photovoltage(0.84 V)and a superior PCE(9.4%).It is impressive that the coordination environment of Cu(II)complex with pentadentate ligand remains basically unchanged after addition of TBP,which is in stark contrast to the common bipyridine complex[Cu(tmby)₂]^2+/+(tmby=4,4?,6,6?-tetramethyl-2,2?-bipyridine).As a consequence,DSCs based on[Cu(tme)]^2+/+complexes exhibit an excellent long-term stability and maintain more than 90% of the initial efficiency after 400 h under continuous illumination,which outperform the reference devices incorporating the bipyridyl counterpart(less than 80%).This work thus provides a new avenue for future design of stable copper redox mediators in DSCs.We further applied the combination of copper complex[Cu(tme)]^2+/+and2,2,6,6-tetramethylpiperidine-1-oxygen radical(TEMPO)to form a tandem electrolyte DSCs.After adding TEMPO,the efficiency of[Cu(tme)]^2+/+-based cell devices has been greatly improved.The open-circuit voltage has been increased from 0.67 V to 0.87 V.According to the analysis of diffusion coefficient and electrochemical impedance,it was found that the introduction of copper complexes can reduce the charge transfer resistance at the counter electrode-electrolyte interface,and thereby accelerate the rate of electrolyte regeneration.At the same time,the introduction of TEMPO improves the open-circuit photovoltage of the devices,and achives a longer electron lifetime.The results demonstrate that the application of[Cu(tme)]^2+/+and TEMPO tandem electrolyte is an effective strategy for further enhancing the photovoltaic performance of DSCs.