Study On The Surface Polarity And Catalytic Properties Of Light Control Lead Iodide

With the development of social economy,a series of environmental problems burst.How to make full use of energy and effectively degrade pollution has become the focus on solving problems.Among multiple solutions,using semiconductor material with photovoltaic effect and photocatalytic ability becomes the breakthrough to solve the problem.A semiconductor material to produce photovoltaic response and participate in the photocatalytic process mainly depends on photoinduced charge separation,migration and recombination process.The behaviors of the photogenerated charge mostly take place in the surface of the semiconductor,so the research of the photoelectric properties of the surface of the semiconductors can bring a way for improving the photovoltaic response and photocatalytic efficiency.PbI₂ is a p-type semiconductor material with wide band gap of 2.4 eV.It has a high atomic coefficient,wide band gap,high resistivity and lifetime of carrier mobility,and other advantages.It can be more effective utilization of solar energy,which makes it have the potential to be used in photovoltaics,detectors,sensors and photocatalysis.But the application of PbI₂ is seriously limited due to the little research about the generation,transport and recombination of photogenerated charge.Based on the above reasons,PbI₂ and annealed PbI₂ were adopted for our study.Surface photovoltage?SPV?,field induced photovoltage?FISPV?and transient photovoltage?TPV?measurements were used to study the behaviors of the photogenerated charge carriers.Also the photocatalytic degradation of MO experiments were conducted.Seeking the inherent relationship between the behavior of the photogenerated charge carriers and the photocatalytic reactions is the main purpose in our studies.In this paper,the preparation,properties and surface modification of PbI₂ and annealed PbI₂ were carried out in two aspects.1.The PbI₂ microcrystals were synthesized by solution method,and the band gap was 2.39 eV.The SPS responses indicate the existence of defect states on the surface,which leads to the surface photovoltaic inversion under the sub bandgap illumination.The photovoltaic inversion can be attributed to the surface state about 0.43 eV above the valence band edge.Under the different light illumination,the generation of photo induced charge is different,and the corresponding voltage decay time is different,which results in different MO photocatalytic results.2.The PbI₂ microcrystals was annealed at 520 K for 10 min,20 min and 30 min,respectively.With the extension of annealing time,the atomic ratio?Pb:I?of the annealed samples was closer to 1:2,and the absorption spectrum was expanded,so as the band gap increased.The annealing results in the decrease of surface defects,but the effect of inversion layer is increased,and the effect of the inversion layer is strengthened gradually with the increase of the applied bias.