Synthesis and characterization of mixed iodide–bromide methylammonium lead perovskite

Abstract

The research field of perovskite based solar cells has recently been developed as the most promising candidate for next-generation because of their high efficiency solar cell technology that is compatible with low-cost, low-temperature processing, long-term stability and simple structure of solar cells production such as the hybrid halide perovskite CH₃NH₃PbI₃ in solar cells have high power conversion efficiency exceeding 22%. However, the unstable nature of perovskite was observed when exposing it to continuous moisture, illumination and high temperature obstructing the commercial development in the long run and thus becoming the main problem that needs to be solved immediately. In this work, the preparation of organic – inorganic halide perovskite by mixing halide group between iodide with bromide, CH₃NH₃PbI_xBr_3-x compound under the annealing temperature condition was investigated. The structure of the product was identified by X-ray diffraction (XRD). In addition, High Resolution SEM image was used to study the presence morphology of crystalline domains within the sample. We examine the thermal properties of samples using Thermogravimetric analysis (TGA) and Simultaneous Thermal Analyzer (STA). To check the variation of optical properties in these compounds, we measured the UV-visible absorption spectroscopy and X-ray Photoelectron Spectroscopy (XPS) which showed the survival of organic group. It is concluded that the annealing affects phase formation and thermal stability of CH₃NH₃PbI_xBr_3-x compounds. A small powder amount of lead bromide (PbBr₂), a product of the degradation, was observed with increasing annealing temperature. Accordingly, appropriate annealing temperature should be chosen to produce a high efficiency photovoltaic.     

Effect of temperature and stoichiometry on the long-range 1:2 cation order in BaZn1/3Ta2/3O3

We report on the compositional stability range, the degree of atomic order and Raman and optical spectra of the off-stoichiometric BaZn_1/3Ta_2/3O₃ (BZT) within the BaO–ZnO–Ta₂O₅ ternary diagram. Almost all off-stoichiometric BZT compositions equilibrated at 1200?°C show significant degree of the long-range 1:2 cation order ranging from 60% to 80%. Ceramics equilibrated at 1550?°C and annealed at 1450?°C show strong effect of composition on the 1:2 order. The regions where an 1:2 atomic order is robust to the deviation from stoichiometry include the off-stoichiometric compositions along the BZT–Ba₄Ta₂O₉, BZT–Ba₃Ta₂O₈, BZT–BaTa₂O₆, BZT–Ta₂O₅, BZT–ZnTa₂O₆ and BZT–Zn₄Ta₂O₉ (pseudo) tie lines. At the same time ceramics formulated along the BZT–BaO, BZT–ZnO, BZT–BaZnO₂, BZT–Ba₂ZnO₃ tie lines and BZT–‘Ba₃ZnO₄’ pseudo tie line show complete disorder. There is a very close correlation between the degree of the 1:2 order on one hand and the unit cell volume and lattice distortion on the other hand. The ordered BZT show contraction of the unit cell whereas disordered ceramics show expansion of the unit cell in the off-stoichiometric region. The pronounced signatures of the order-disorder phase transition in the Raman and optical spectra are discussed.     

Correlation between the 1:2 atomic order and microwave dielectric loss in the off-stoichiometric Ba(Zn1/3Ta2/3)O3

We report close correlation between the 1:2 atomic order and microwave dielectric loss in the off-stoichiometric Ba(Zn_1/3Ta_2/3)O₃ (BZT). Small off-stoichiometric deviations have a large effect on the ordering and Q?×?f values. The Ba₄Ta₂O₉-BZT-‘Zn₄Ta₂O₉’ pseudo tie line separating the Ta-rich and Ta-poor regions also demarcates the 1:2 ordered and disordered BZT. The low-loss off-stoichiometric BZT ceramics are located in the 1:2 ordered region of the BaO-ZnO-Ta₂O₅ phase diagram. Without exception the disordered BZT ceramics show high dielectric loss. Stoichiometric BZT with 1:2 atomic order shows Q?×?f?=?113?THz. The off-stoichiometric 1:2 ordered BZT ceramics with the highest Q?×?f?>?200?THz are located in the ZnO-deficient part of the ternary phase diagram.