Charge Transport Performance Of Nafion-based Redox Polymer Film In Atmosphere

The redox polymer is a candidate of the solid organic charge (electron or hole) transport material. The redox polymer proposed by Bard and Murray has been applied for chemically modified electrodes for some time. Murray synthesized some polymer complexes and studied their charge transport performances in the absence of liquid solvents later, but these materials still bathed in polar organic solvent can't be applied in the light emission and solar cell devices which must work in atmosphere.This thesis focuses on synthesizing several novel solid or quasi-solid organic charge transport materials, improving their charge transport performances and developing methods for estimating charge transport performances . The works can be divided into two parts: (1) Nafion–based redox polymer films are synthesized and sandwich-type cells are constructed, (2) The charge transport performances of Nafion–based redox polymer films and solid cells in atmosphere are characterized by cyclic voltammetry (CV) and ectrochemical impedance spetroscopy(EIS). Furthermore, the relationship between the charge transport performance of redox polymer film in sandwich-type cell and the electrode interface structure also were discussesd. The main results are summarized as follows:1. Nafion–based redox polymer films are synthesized and sandwich-type cells are constructed with two methods.Their constructure parameters were studied.The Nafion[M(bpy)32+](M=Ru,Fe) solid films prepared by drop-coating a Nafion solution on a ITO grass frist and exchanging H+ ions using M(bpy)32+ ions second (method 1) are about 15 micrometers in thickness.The Nafion[M(bpy)32+, polyethylene glycol (PEG)](M=Ru,Fe) solid films prepared by drop-coating a Nafion solution containing M(bpy)32+ ions and PEG on a ITO grass (method 2) 20 micrometers in thickness. The probability of short circuit of ITO/Nafion[Ru(bpy)32+,PEG]/ Au sandwich-type cell is lower than ITO/Nafion[Ru(bpy)32+]/ Au's. The concentration of the H+ sites in these Nafion films is about 0.13 mol.L-1.2. Characterization methods of charge transport performances of Nafion–based redox polymer films and sandwich-type cells in atmosphere using cyclic voltammetry (CV) and ectrochemical impedance spectroscopy (EIS) are established(1) CV data anlysis method for characterizing the charge transport performances of Nafion–based redox polymer films is established. The apparent charge transfer diffusion coefficients,Dct,of the Nafion[Fe(bpy)32+,PEG] film and Nafion[Ru(bpy)32+,PEG] film in ITO/Nafion[M(bpy)32+,PEG]/Au(M=Ru,Fe) sandwich-type cells are about 10-6~10-7 cm2·s-1 and the mobilities of the electrons or holes,μe orμh , are about 10-4~10-5 cm2·V-1·s-1.(2) The results of EIS show that both of electrodes have similar equivalent circuits which contain charge transfer resistance, Warburg impedance,constant phase element(CPE) which is related to interface double layer capacitance .The bulk impedance of film is ohmic. The Dct,μof Nafion[Ru(bpy)32+ , PEG] film are 10-8~10-7cm2·s-1 and 10-7~10-6cm2·V-1·s-1, respectively .(3) There are some differences between the Dct of Nafion[Ru(bpy)32+,PEG] film obtained by CV and that by EIS .The main reason is that the concentrations of the oxidation and reduction sites in Nafion–based redox polymer films when experiments of CV and EIS are different.3. A polyaniline (PANI) layer is added to the interface of ITO electrode and the redox polymer film to improve the charge transport performances of Nafion–based redox polymer film and solid cell.(1) The results of CV show that the Dct andμof the Nafion–based redox polymer film in ITO/PANI/Nafion[M(bpy)32+,PEG]/Au(M=Ru,Fe) sandwich-type cells could be increased and the operating current of the cells under 600mV bias could be increased by almost 100 times . The charge transport performance of this redox polymer films is comparable to some organic charge transport materials'. In addition, the Dct andμof this redox polymer film have just reduced slightly after 30 d kept in atmosphere. Therefore, the redox polymer film is sufficiently stable . (2) The results of EIS show that a conducting PANI layer added to the interface of ITO electrode and the redox polymer film can decrease the impedance of solid cell.contact impedance disappear , and charge transfer resistance,Warburg impedance of ITO electrode decrease.The Dct,μof Nafion[Ru(bpy)32+,PEG] film are 10-7~10-6cm2·s-1,and 10-5~10-4 cm2·V-1·s-1,respectively .(3)Three different oxidized form PANI layers were added to the interface of ITO electrode and the redox polymer film . The results of EIS show that only partially-oxidized PANI layer can modify the interface between ITO and the redox polymer solid film to improve the charge transport performance.