| In recent years, material of lead halide perovskite(CH3NH3PbX3) is developed rapidly and concerned widely in photovoltaic devices(solar cells) due to the following advantages: low cost, easy to manufacture; excellent carrier transport capacity; high light absorbing ability. In this paper, we aimed at preparing CH3NH3 Pb I3 films on the MgO(100) substrate by co-evaporation method. And the effect of growth parameters on the microstructure of CH3NH3PbI3 thin films was explored. We studied the quality of CH3NH3PbI3 films prepared under the optimal conditions. On these bases, CH3NH3PbI3 solar cells were obtained. The detailed research contents and results are summarized as follows:(1) The preparation of CH3NH3PbI3 films on the MgO(100) substrate by co-evaporation method with CH3NH3 I and Pb I2 as the evaporation source was studied. XRD, SEM, EDS, AFM and other methods were used to realize the films microstructure. The effects of process parameters such as temperature, vacuum degree, deposition time, substrate temperature and annealing temperature on the microstructure of CH3NH3PbI3 thin films were investigated. The basic process was obtained: back vacuum is 1.0×10-3 Pa, CH3NH3 I evaporation temperature is 120 ℃~150 ℃, Pb I2 evaporation temperature is 305 ℃~330 ℃, deposition time is 3.5 h. The results indicate that CH3NH3PbI3 films have a preferred orientation(110), the surface of films is flatness, FWHM is 2.7 ° and RMS is 8.2 nm.(2) The effect of in-situ annealing on the quality of CH3NH3PbI3 films was studied. The effect of annealing process on the microstructure of the films was investigated by in-situ annealing of CH3NH3 Pb I3 films prepared under the optimized conditions. The optimal annealing process of CH3NH3 Pb I3 films was obtained: annealing temperature is 100 ℃, annealing time is 0.5 h(other processes are unchanged). After in-situ annealing, the preferred orientation(110) of films is further improved. The grains have a lumpy structure with good continuity according to the cross-section SEM image. SEM, AFM test results show that the quality of CH3NH3 Pb I3 films was improved, FWHM is 1.1° and RMS is 3.9 nm.(3) The optical property of CH3NH3PbI3 thin films under optimum process have been discussed. Raman spectra, transmittance spectra and PL spectra of the prepared CH3NH3PbI3 films were tested. The results are as follows: Raman spectra shows peaks at about 141 cm-1 and 286 cm-1, which can be assigned to the vibration of organic cations and torsional mode of the methylammonium cations, respectively. Visible light transmission shows that the average transmittance is more than 60% and the films exhibit a clear absorption edge around 770-780 nm wavelength. According to Tauc equation, Eg is 1.58 eV; PL spectra show a strong peak at 784 nm(1.58 eV), the peak is considered as the inherent CH3NH3PbI3 emission peak(FWHM=24 nm); Photoluminescence can be used to estimate the diffusion length CH3NH3 Pb I3 films and the length is ~ 100 nm. All the results illustrate that the good quality of CH3NH3PbI3 films were obtained on MgO substrate.(4) The co-evaporation method was used to prepare the CH3NH3PbI3 solar cell. The effect of annealing process on the performance of CH3NH3PbI3 solar cells was studied. The results show that the energy conversion efficiency of the solar cell device(η%) is 5.0%, the fill factor(FF) is 43.7%, short circuit current(Jsc) is 14.4 mA.cm-2, the open-circuit voltage(Voc) is 0.72 V after in-situ annealing(annealing temperature is 100 ℃, annealing time is 0.5 h). Also, the solar cell is a complex system,and its performance can be effected by many factors. The performance of solar cell in this paper need to be further improved. But, preliminary results show that the prepared CH3NH3PbI3 films can be used to prepare the solar cell. |
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