The Applications Of Water-dispersed TiO₂ Nanocrystals In Solar Energy Conversion

TiO₂ is widely used in photocatalyst and photovoltaic devices due to the advantages of non-toxic,good thermal stability and high dielectric constant.The researches on photocatalytic and photoelectronic properties of water-dispersed TiO₂ nanocrystals are rare.In this case,we demonstrate the fabrication of aqueous-processed polymer/nanocrystals hybrid solar cells based on aqueous-processed TiO₂ electron extraction layer and the preparation of water-dispersed TiO₂-graphene nanocomposite for photocatalytic water splitting.Specifically,there are two aspects introducing in detail in the following paragraphes.In chapter II,the water-dispersed TiO₂ nanocrystals are used in hybrid solar cells.TiO₂ is often served as cathode interface modification layer owing to its high electron mobility,good light transmission and deep valence band.In the past,the preparation of TiO₂ is generally based on sol-gel method.The crystallinity and conductivity is poor,which is attributed to the large amount of residual alkyl chain.In addition,the TiO₂ colloidal solution is sensitive to humidity,and it can not be used in high humidity conditions.In this case,the water-dispersed TiO₂ nanocrystals with small size are prepared and used as the cathode interface layer to improve the above shortcomings.The TiO₂ film has super hydrophilicity and good crystallinity after annealing.Therefore,the device performance is obviously improved,and a PCE of5.53% is achieved for the aqueous-processed polymer/NC hybrid solar cells based on the aqueous-processed TiO₂ electron extraction layer.The PCE is a record for hybrid solar cells at that time.And the humidity resistance is greatly improved with the aqueous-processed TiO₂ electron extraction layer.In chapter III,the water-dispersed TiO₂-graphene nanocomposite are prepared for photocatalytic water splitting.Because of its excellent properties,TiO₂ is often used as photocatalyst.However,,the use of visible light is less due to its wide band gap（3.2eV）.In addition,TiO₂ absorbs light produce the photoinduced electron-hole pairs,the photoproduced electrons and holes can recombine quickly,which can reduce the efficiency of photocatalytic reaction and the efficency of H2 production greatly.Basedon the above influencing factors,a variety of methods have been researched to improve photocatalytic efficiency,including addition of electron donors（EDTA,methanol ethanol,lactic acid,CN-and formaldehyde）,carbonate salts,noble metal loading,ion doping and composite semiconductors.In this chapter,we use TiO₂ and graphene to produce the photocatalyst TiO₂/GO、TiO₂/G composite,and compare the hydrogen production performance of graphene oxide and reduced grapheme.And the mass fraction of graphene was adjusted,the best hydrogen production effect is based on the composite of TiO₂ with 1% reduced graphene.In summary,we demonstrate the fabrication of aqueous-processed polymer/nanocrystals hybrid solar cells based on aqueous-processed TiO₂ electron extraction layer with improved device performance and humidity resistance.On the other hand,the water-dispersed TiO₂-graphene nanocomposite are prepared for photocatalytic water splitting.We realize the solar energy conversion and contribute to the future of energy and sustainable development.