The Preparation And Photoelectrical Properties Of TiO₂@SrTiO₃ Nanometer Nanoarrays

As the fossil energy exhausting and causing serious environmental problems,people began to explore clean renewable energy.Among all the methods to meet the problems mentioning above,the photoelectrochemical（PEC）system uses semiconductor electrodes to split water into hydrogen energy and the solar power generation provides a method to convert solar energy into electricity.Photoanode is an important part of the two devices.Among all the various photoanode semiconductor materials,TiO₂ is one of the most attractive candidates due to its low-cost,nontoxicity,excellent chemical stability and high photocatalytic activity.However,a major limitation of TiO₂ photoanode materials is the low efficiency owing to the poor separation and transportation behaviors of photogenerated charge carriers,leading to photoexcited electron-hole recombination that prevails in the bulk.The core-shell structure of nanomaterials can compensate for this defect.It can not only protect the integrity of the core material,but also change its surface properties,thus promoting the composite materials’optical properties,electrical properties and so on.The core-shell structure of nanomaterials attracts a lot of attentions.This paper is based on TiO₂ core-SrTiO₃ shell nanowire-arrays as the photoanode in the photoelectrochemical system and perovskite solar cells.The TiO₂ core-SrTiO₃shell nanowire-arrays（NWAs）were synthesized by hydrothermal method.It is found that the core-shell structured heterogeneous materials have excellent performance in photoelectrochemical system and perovskite solar cells.The results are as follows:（1）We have successfully converted TiO₂ NWAs to TiO₂ core-SrTiO₃ shell heterostructured NWAs via a simple hydrothermal method with different conversion times.TiO₂ NWAs can be analyzed by XRD,showing that the TiO₂ nanowires are along the（002）crystal growth preferred rutile phase,and SrTiO₃ is cubic perovskite structure.The core-shell structure of the material was determined by SEM,HRTEM and EELS.（2）The TiO₂ core-SrTiO₃ shell NWAs exhibit greatly enhanced PEC water splitting performance under AM 1.5G illumination in comparison with the pristine TiO₂ NWAs.The highest J_ph（1.43 mA/cm² at 1.23 V versus RHE）andη_separation（87.7%at 1.23 V versus RHE）were achieved on⁴.5-nm-thick STO shell obtained with the conversion time of 2h,which are 1.83 and 1.79 times higher than the bare TiO₂ NWAs.（3）The polarization performance of TiO₂ core-SrTiO₃ shell NWAs can be improved or decreased by applying positive or negative polarization and high temperature annealing.It is proved that the ferroelectric effect of STO has affected the performance of PEC water splitting.（4）The results of UV-Vis absorption spectra show that the thickness of STO shells has little effect on light absorption,and thus the influence on the performance of PEC water splitting is insignificant.Then,the injection and separation efficiencies of TiO₂ core-SrTiO₃ shell NWAs were calculated by the measurement of the TiO₂core-SrTiO₃ shell NWAs in a sustained-release solution containing hole scavenger.The results show that the separation efficiency of TiO₂ core-SrTiO₃ shell NWAs is significantly improved.The origin of the remarkable improvement in PEC performance is attributed to the ferroelectric polarization-induced upward band bending of the TiO₂ core,effectively driving photogenerated charge carriers’separation and transport for PEC water splitting.This work demonstrates that ferroelectric polarization can be a promising tool to improve PEC performance for artificial photosynthetic system.（5）The TiO₂ core-SrTiO₃ shell NWAs are used as the electron transport layer in the perovskite cell.The highest Voc（1.02 V）,J_ph（22.7mA/cm²）,FF（56.99%）andη（13.22%）were achieved on⁷80-nm-thick TiO₂ core-SrTiO₃ shell NWAs obtained with the reaction time of 2h of TiO₂,which are higher than the bare TiO₂ NWAs.This is because（i）the nanowire array provides a direct channel for electron transport,（ii）SrTiO₃ has a high conduction band,（iii）the band of SrTiO₃ can be matched with the band of TiO₂,（iv）SrTiO₃ has a cubic perovskite structure,（v）high electron mobilityof SrTiO₃ can improve the performance of perovskite batteries Performance.