Preparation And Photocatalytic Semiconductor Thin Film Photovoltaic Research And Performance

Environment problem is becoming more and more serious, because of theexcess consumption of fossil energy and its decreasing resources. Consequently,finding new and clean energies has been a global issue. Solar energy is one of theimportant main routes to develop future sustainable energy. Since its first discoveryin1839, photoelectric conversion has achieved a series of important progressesincluding both fundamental theories and practical applications. Photocatalysis anddye-sensitized solar cells were proposed in the1970s and1990s, respectively. Theyfollow the same basic theory that photons excite the bandgap of semiconductor toproduce the photo-generated electrons (negative charge) and holes (positive charge),which then lead to redox species or photocurrent in the circuit.This thesis focuses on the following topics: synthesis of novel semiconductorfilms with visible light response, exploration of the relationship between themorphology of semiconductor films and its light absorbency, study on therelationship of light absorbency and photoelectric conversion, and investigation ofthe promoting effect on the electron mobility by adding functional graphene into thesemiconductor films. The main work can be divided into following4parts.(1) TiOF2mesoporous films were prepared by dipping-coating alcohol solutioncontaining TiF4onto a glass surface, followed by evaporation induced self-assemble.The formation mechanism was also revealed through characterizations of mapping,FT-IR, NMR and so on. Such TiOF2mesoporous films could be activated by visiblelights. Meanwhile, they also showed the high crystallization and binding strength dueto chemical bonding between TiOF2film and the SiO2substrate. As a result, theyshowed high activity and durability during photocatalytic degradation of RhodamineB in aqueous solution under visible light irradiation, which could be further optimizedby adjusting the TiF4concentration and reaction temperatures during preparation ofTiOF2films. These TiOF2films could also be coated onto other Si-base substrates bycovalently bonding, showing good potential in practical applications.(2) The TiO2photonic films were synthesized by solvothermal reaction of Ti foil, TiF4and tert-butyl alcohol at160oC. Such TiO2films showed enhanced lightabsorbance ability in certain wavelength. By optimizing reaction period, TiF4and/orHF amount, the TiO2films displayed strongly selective absorbance of lights withcharacteristic wavelengths. During photocatalytic degradation of rhodamine B andmethylene blue under visible lightirradiation, the TiO2films showed enhancedactivity at the irradiation of lights with characteristic wavelengths corresponding tothe strong light absorbance. The relationship between the selective light absorbanceand photocatalytic activity were investigated based on detailed characterizations.(3) TiO2microspheres with tunable chamber space (solid spheres, core shellspheres and hollow spheres) were synthesized by solvothermal reaction of mixedsolvents (alcohol, glycerin, diethyl ether) and TiOSO4at desired reaction periods.These microspheres were introduced into the dye sensitized solar cells (DSSCs) as ascattering layer encapsulated by two TiO2films comprised of uniform tiny TiO2nanoparticles, which exhibited the promoting effect on the light harvesting and cellefficiency owing to the multiple light-reflections in the microsphere chambers andthe internal light reflections within the TiO2films, together with the reduced electricresistance for the electron-transfer.(4) Carboxyl-functionalized graphene was synthesized by Diels-Alder reactionunder microwave irradiation in which the graphite played the role as diene and themaleic anhydride was used as dienophile. Based on the investigation of the influenceof either the reaction temperature or the maleic anhydride concentration on thegraphene growth, the optimum conditions were determined as the reactiontemperature of180oC and the graphite/maleic anhydride weight ratio of1/1.5. Whenthe as-received graphene were treated under vacuum at elevated temperatures, thereverse Diels-Alder reaction took place, leading to the recovery of the conductivity.The square resistance measurements showed the recovered graphene’s conductivitywas as10times as the functional graphene. Such carboxyl functional group played arole as a bridge between graphene and TiO2semiconductor films, leading to thegreat increase of electron mobility of the TiO2films, which could remarkablypromote photoelectric conversion efficiency. The formation mechanism of carboxyl functional graphene was examined based on detailed characterizations. Meanwhile,the correlation of photoelectric conversion efficiency to the graphene compositionand structure was also explored.