The Research On The Influence Mechanism Of Perovskite Ferroelectric On Photoanode Carrier Transportation

Photoelectrochemical（PEC）water splitting is a process of converting solar energy into green and pollution-free hydrogen energy,which includes two half reactions:water oxidation in photoanode and water reduction in photocathode.Water oxidation reaction process involves four continuous charge transfer,which requires relatively high reaction activation energy.It is of great significance to study high-performance semiconductor photoanode materials for improving PEC water splitting efficiency.At present,the low carrier mobility in photoanode semiconductors leads to the recombination of electron hole pairs,which reduces the efficiency of water splitting.In recent years,the emergence of nanoscale ferroelectric materials provides a new way to solve this problem.It has been shown that the polarization field in ferroelectric materials due to the asymmetric crystal structure can improve the oxidation kinetics and photocurrent of the photoanode.However,for different type carriers with different mobility rates and diffusion lengths,the effect of ferroelectric polarization field on their migration is not clear.Based on the above analysis,this paper took WO₃ photoanode as the research target,optimized the structural parameters of the photoanode,and discussed the photocurrent controlled by different carriers and its related mechanism.Then,ferroelectric material BaTiO₃（BTO）was added into it to build a hybrid photoanode,and the influence of ferroelectric polarization field on the migration of different types of carriers was explored.The main research contents and results of this paper are as follows:1.WO₃ was selected as the photoanode semiconductor.The structure,morphology and optical properties of this semiconductor were characterized by XRD,XPS,SEM and UV-Vis spectroscopy.The results show that the semiconductors WO₃ are nanoparticles with a size of about 100 nm.And it has a monoclinic crystal structure with a band gap of 2.5 e V.2.The density functional theory was used to calculate the mobility of electron and hole in WO₃.The photoanode WO₃ film was prepared by the method of drop coating.The photocurrent rule of WO₃ films with different thickness was explored through experiments of light direction and different loads,and the mechanism of carrier control was studied.The results show that the electron mobility in semiconductor WO₃ is greater than the hole mobility,that is,the electron diffusion length is greater than the hole diffusion length.When the drip coating times are less than 3 times,a thin WO₃ film is obtained.At this time,the front-side illumination photocurrent is greater than the back-side illumination photocurrent,indicating that the hole mobility of the thin film is the main factor of limiting the photocurrent.When the drip coating times are more than5 times,a thicker WO₃ film is obtained.At this time,the front-side illumination photocurrent is less than the back-side illumination photocurrent,indicating that the electron mobility is the main factor of limiting the photocurrent in this case.3.Tetragonal BTO ferroelectric nanoparticles were synthesized by hydrothermal method.The structure and morphology of BTO materials were characterized by XRD,XPS,Raman spectroscopy and SEM.The results show that the synthesized BTO has a tetragonal asymmetric crystal structure,and its morphology is nanoparticle with the size of about 100 nm.4.The optimized BTO was mixed with the above-mentioned thin layer and thick layer WO₃ respectively to prepare the hybrid photoanode,and the influence of the polarization field on the mobility of different carriers was explored through+20 V polarization.The results show that the photocurrent of the thin film hybrid photoanode controlled by hole migration is increased by 210.5%under the action of polarization field,and the carrier separation efficiency is increased 94%.However,under the action of polarization field,the photocurrent of the thick film hybrid photoanode controlled by electron mobility increases by 59.6%,and the carrier separation efficiency increases by32%.The results show that the polarization field can promote the carrier migration and improve the carrier separation efficiency.Compared with the electron migration,the polarization field of ferroelectric has a more significant effect on the hole mobility.This paper provides a new idea and reference for the construction of efficient photoanode.