Nanostructured Semiconductor Materials: Syntheses And Applications In Photoelectrochemical Energy Conversion Area

Solar energy has been extensively thought as a sustainable and clean energy sourcewith huge supply-capacity. Currently, a feasible way for harvesting and conversion ofsolar energy is to take use of the internal photoelectric response process insemiconductor materials, which absorbed incident photons and converted the energy ofthe efficiently-absorbed photons into electric or chemical energy. Traditionalphotovoltaic technologies which based on bulk semiconductor materials have achievedremarkable success. However, further improvement of energy conversion efficiency andreduction of processing cost are limited by the contradiction between the lightabsorption and charge-carriers’ collection in bulk semiconductor photoelectrode. Asdemonstrated experimentally and theoretically by previous investigations,nanostructuring of semiconductor materials are possible to break through this limit,which own several advantages as shown as following:1) It’s possible to construct extensively hetero-junctions by nanostructuring ofsemiconductor materials and then hugely reduce the needed transport distance forphoto-generated charge-carriers, namely reduce the recombination losses of theenergetic charge-carriers in the semiconductors during the transport process.2) The specific surface area of the semiconductor materials could be hugelyenlarged by nanostructuring. The increased specific surface areas raise the efficientphotoactive component of the semiconductor materials to some degree.3) Some particular nanostructured semiconductor materials can break throughthe contradiction of light absorption depth and charge-carriers’ collection distancewhich commonly exist in bulk semiconductor materials, namely can better decouplingthe direction of light absorption and the direction of separation, transport and collectionof charge-carriers.4) Some new physic phenomena may emerge by nanostructuring ofsemiconductor materials, such as quantum confinement effect, photonic crystal effectand reconstruction of energy-band or electric structures of the semiconductor materials. These effects own the possibility to tune the magnitude of band-gap and the intensity ofphotoresponse of the semiconductor materials, and then endow the materials withabundant and tunable photoelectric properties.Based on the possible merits of nanostructured semiconductor materials mentionedabove, we put our effort into exploring the syntheses of semiconductor nanostructuresand exploring their potentials in solar energy capturing and conversion applications. Inthis regard, some classical syntheses methods of nanostructured materials (such ashydrothermal process, electrochemical etching, sol-gel process, chemical solutiongrowth method, ion exchanging method and successive ionic layer adsorption anddeposition process etc) were adopted to fabricate a series of semiconductornanostructures, including: TiO2nanotube arrays, TiO2nanorod arrays, ZnO nanowirearrays, three-dimensional branched ZnO nanowire arrays and TiO2inverse-opalphotonic crystals. Further works were focused on the applications of thesesemiconductor nanostructures in solar energy capturing and conversion by directlyserving as photoactive materials or supports for other photoactive materials (such ascarbon quantum dots and gold nanocrystals). The characteristics and merits of thesesemiconductor nanostructures in the capturing of photons, separation and transport ofphoto-generated charge-carriers and energy conversion were systematically investigatedby characterizations of material structures and compositions, optical measurements,electrochemical measurements and so on.