New Ionic Liquids For Dye-Sensitized Solar Cells

This work had developed non-imidazolium ionic liquids for high efficiency and low cost DSC application and investigated their internal transmission mechanism.The main conclusions are summarized as follows.Tetrahydrothiophenium and trialkylsulfonium based ionic liquids were synthesized,and their structure and components determined by ¹H NMR,ESI-MS, IR and elemental analysis.Basic physical properties versus temperature of the tetrahydrothiophenium and trialkylsulfonium based ionic liquids and electrolytes were measured by density meter,viscometer,conductivity meter and electrochemical workstation. The suitable ionic liquids for DSCs were selected out,such as T₂DCA,T₂TCM, S₂₂₁DCA.In addition,the viscosity-dependent transport of triiodide in ionic liquid electrolytes with high iodide concentration can be described by a physical diffusion coupled bond exchange mechanism.The above ionic liquids were used as electrolytes for DSCs,and the efficiencies had been tested under simulated sunlight.Electrolytes A: T₂I/T₂DCA/I₂/NBB(6:4:1:1,molar ratio) or electrolyte B:T₂I/T₂TCM/I₂/NBB (6:4:1:1,molar ratio) were injected into the sandwich cells for devices A or B.The power conversion efficiency(η) of device A and device B under simulated full sunlight(air mass 1.5 global,100 mW·cm^-2) has reached 6.5%and 6.9%, respectively.For the first time,such a high efficiency under the AM 1.5G sunlight is obtained for DSC with solvent-free non-imidazolium ionic liquid electrolytes. Moreover,the power conversion efficiency(η) of the device based on S₂₂₁I/S₂₂₁DCA ionic liquid electrolyte has reached 7.2%under simulated full sunlight.Photovoltage and photocurrent transient,and electrochemical impedance measurements were employed to reveal the charge recombination at the titania/electrolyte interface,and the influence of different anions on electron life time(Ï„_n),diffusion coefficient(D_n) and diffusion length(L_n).We have found that some anions of ionic liquid electrolytes such as dicyanoamide have a significant influence on surface states and electron transport in the mesoporous semiconducting film.