| Organic-metal perovskite CH3NH3PbX3 is widely used in solar cells,photodetectors,lasers and other fields because of high optical absorption coefficient,long carrier lifetime and high carrier mobility.In recent years,perovskite has great potential application prospects as a gas sensitive material due to its special properties in gas sensitivity.The quality of perovskite film was studied and the response of CH3NH3PbI3 films to NH3 environment was summarizes in the paper.The results are listed as follows:NH3·H2O was used as additive to improve the morphology of perovskite films in the two-step solution method.The results show the PbI2 film is porous by the addition of NH3·H2O.As the NH3·H2O increased,the surface porosity of PbI2 films increased,the grain size of perovskite films improved and the residual amount of PbI2 in the films reduced.The residual amount of PbI2 is almost zero,the grain size of perovskite increased to about 500 nm and the average grain size is about 496 nm when the NH3·H2O content is 5%.The perovskite film has good smoothness.Perovskite films prepared by one-step method and two-step method were compared.Perovskite films had higher crystallinity,lower residual PbI2 content and preferred orientation growth of perovskite by using one-step method.Perovskite films prepared had good morphology,cubic grain shape,uniform grain size distribution and high surface coverage by using two-step method.Perovskite films were prepared by pulsed electromagnetic field assisted two-step spin coating method,the application of pulsed electromagnetic field made the PbI2 films rough.Perovskite films grew along with the structure of the PbI2 films,resulting in incomplete reaction with CH3NH3I and large amount of residual PbI2.On the other hand perovskite films were prepared by pulsed electromagnetic field assisted two-step solution method,the residual amount of PbI2 in perovskite films by pulsed electromagnetic field treatment was reduced,and the grain size of perovskite films was refined from 430nm to 350nm,pulsed electromagnetic field improved the surface coverage of perovskite films.The residual amount of PbI2 in perovskite film was almost zero and the coverage rate was the highest when the pulse voltage was 400 V.The color of perovskite film changed from black brown to light yellow under NH3environment for short time.Then the film could return to light black after perovskite film was removed from NH3 environment.The color change of perovskite film shows reversibility.The color of film first changed from black brown to light yellow and then to colorless when the reaction time between perovskite film and NH3 was prolonged.The film showed light yellow after it was removed from NH3 environment,and the color change of the film was irreversible.The interaction between NH3 and CH3NH3PbI3,caused the reversible reaction of perovskite film color change.NH4PbI3 reacted with NH3 environment caused the irreversible reaction of perovskite film color change,NH3 would adsorb on the surface of NH4PbI3 and forming colorless NH4PbI3·xNH3.NH3 on the surface of perovskite film could desorb automatically after the film was removed from NH3 environment,thus the film could restore to pale yellow NH4PbI3.. |
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