Optical Property Of Perovskite CH₃NH₃PbI_xX_3-x Films Deposited By The Two-step Liquid Phase Deposition

The polycrystalline perovskite CH₃NH₃PbI₃ and halide element（Cl,Br）doped CH₃NH₃PbI_xX3-x films were fabricated on the glass by the two-step liquid phase deposition with diffrerent experiment parameters such as PbI₂ rotation rate,soaking time,colloidal solution concentration,glue temperature.The effect of the deposition parameters was intensively investigated on the microstructure and optical property of the films with use of XRD spectra,field-effect scanning electron microscope,spectrophotometer and the photoluminescence spectra.And the mechanism for the formation of perovskite CH₃NH₃PbI₃ films was explained on the basis of the above experimental data analysis.The main results were listed below:（1）The <110> preferred oriented CH₃NH₃PbI₃ films were prepared.The average grain size of the CH₃NH₃PbI₃ films decreases and the absorption edge blue shifts initially and then red shifts with the increase of PbI₂ rotation rate.The blue and red shifts of the absorption edge are closely related to the enhanced preferred <110>orientation and the enhanced surface effect of the particle size,respectively.The luminescent intensity of CH₃NH₃PbI₃ film reached the maximum at rotation rate of2750 r/min.（2）When the soaking time is 90 s,the residual amount of PbI₂ in CH₃NH₃PbI₃ film is the smallest,which indicates that it is impossible to remove residual PbI₂ completely by increasing the soaking time alone.The crystallization of the films is enhanced with the appearance of holes,and the luminescent intensity of the films reached the maximum at 150 s with the increase of soaking time.（3）The PbI₂ particles located around the defect and void positions are preferable to react with CH₃NH₃ I to form the CH₃NH₃PbI₃,but the MOF（Metal-Organic Frameworks）sandwich structure of PbI₂-IPA-CH₃NH₃ I is formed on dense surface when soaking.With the IPA molecules escaped when annealing,PbI₂ and I-ions from the hydrolyzed CH₃NH₃ I formed the cubic frame structure.CH₃NH₃+ ions diffuse into the interstite positions in the cubic frame structure under the electrostatic force and form perovskites CH₃NH₃PbI₃ films in the end.（4）When the PbCl₂ and PbI₂ molar ratio（Rmol [PbCl₂:PbI₂]）> 1:9,Cl-ions go into the perovskite structure.Compared with the diffraction peaks of CH₃NH₃Pbl3,the diffraction peaks of CH₃NH₃PbI_xCl3-x shift slightly to the big angle.Particles adhesion phenomenon appears in the films and the crystallization of the films weakens when Rmol [PbCl₂:PbI₂] > 3:7.With the increase of Rmol [PbCl₂:PbI₂],the absorption edge of CH₃NH₃PbI_xCl3-x films blue shifts weakly.The absorption edge of the films adjusted in the range between 1.57 eV and 1.62 eV and the luminescent intensity effectively enhances by Cl-doping.（5）Compared with CH₃NH₃PbI₃,the diffraction peaks of the CH₃NH₃PbI_xBr_3-x moves to a large angle.Because Br-radius is less than the I-,which results in the interplanar spacing decreased and the peak moving to a large angle.When PbBr₂ colloidal solution concentration is 0.8 M,the surface coverage is highest and the particles are uniform.The absorption edge ranges from 1.77 eV to 1.84 eV by Brdoping.The photoluminescence peak position of CH₃NH₃PbI_xCl3-x is near the 700 nm which obviously blue shifts compared with CH₃NH₃PbI₃.The photoluminescence peak of films is obviously higher than that of CH₃NH₃PbI₃ films.