Layer-by-layer Self-assembly Of Conducting Multilayers And Research On Their Electrical, Electrochemical, And Photovoltaic Properties

Energy is a hot issue on a global scale in recent years. With the sharply decreaseof energy reserses and its badly influence on the environment, more and more scholarsbegin to value the renewable energy which has abudent sources and pollution-free.However, the renewable energy is both limited in geography and has high setup andmaintenance cost. Comparatively solar has a energy great prospect and hence solarenergy received extensive attention. As a component of great importance part indye-sensitized solar cells (DSSCs), the counter electrode (CE) has a significant effecton the fill factor (FF) which is one of photovoltaic parameters used to measure theperformance of solar cells. Increasing the reaction area of CE can promote reaction ratetremendously, thus further enhancing the conversion efficiency of DSSCs. In1991,Decher et al. reported a simple self-assmebly method with the electrostatic interactionbetween cationic and anionic polyelectrolytes as driving force to fabricate multilayerfilms which have large special surface and have a good prospect in the application ofCE. In this paper, the multilayer films with high conductivity and high catalyticactivity are synthesized by the self-assembly method and then conductive mechanismis investigated. It’s innovative and significant for the application of as-preparedmultilayer films to the CE materials of DSSCs.In chapter2, poly(dimethyl diallyl ammonium chloride)(PDDA) and graphiteoxide (GO) nanoplatelets are used to prepare (PDDA/GO)nconductive multilayer withelectrostatic self-assembled method. The results show that the (PDDA/GO)nconductive multilayer films grow linearly and uniformly, the thickness of eachPDDA/GO conductive multilayer film is basically identical. The redox reaction inH2SO4aqueous solution is controlled by the diffusion. Meanwhile, the charge transfer in redox step is controlled by the diffusion of charge in the films. The film resistance of(PDDA/GO)nconductive multilayer films is approximate constant while their electricalconductivity increases linearly with the increase of the bilayer number, which indicatesthat with the increase of the number of bilayer, the surface charge of the filmsaccumulate linearly, showing the electron tunneling effect. The photoelectrcity testshows that photocurrent responses of (PDDA/GO)nconductive multilayer films arehighly dependent on deposition cycles of GO nanosheets, and photocurrent densityincreases rapidly with deposition cycle. This indicates photogenerated electrons havealso a tunneling effect from bottom to top GO layers, and this can be applied in the CEof DSSC.In chapter3, we successfully fabricate the Layer-by-layer self-assembly ofconducting polymer polypyrrole (PPy) and GO nanoplatelets by using electrostaticself-assembled method in chapter2. The results show that the growth pattern of(PPy/GO)nconductive multilayer films is uniform linear growth. The redox reaction inH2SO4aqueous solution is controlled by the diffusion. Simultaneously, the chargetransfer in redox step is controlled by the diffusion of charge in the films. The filmresistance of (PPy/GO)n conductive multilayer films does not change with the increaseof the bilayer number, but its conductivity increases linearly, showing the electrontunneling effect. The catalytic activity of conductive multilayer films to electrolyte andthe electrical conductivity increase linear correlation with the number of bilayer, whichcompletely conform to the requirements on the performance of the CE of DSSC. Theexperimrntal results indicate that the energy conversion efficiency of DSSC based on(PPy/GO)nconductive multilayer films increases with the increase of the number ofbilayer, and the maxmium efficiency of4.86％is obtained.In conclusion,(PDDA/GO)nand (PPy/GO)nconductive multilayer films areprepared by self-assembly method. Conductive multilayer films have uniqueadvantages in electrical, electrochemical, and photovoltaic performance, and the(PPy/GO)nconductive multilayer films are applied in the CE of DSSC. Self-assemblymethod is applied to DSSC, and it promotes the development of the CE of DSSC.