Low-Temperature In-situ grown MAPbBr3 Crystals and their Characterizations
Kunchanapalli Ramya a, Arindam Mondal a, Satyajit Gupta a, Sabyasachi Mukhopadhay a
a SRM University AP, Andhra Pradesh, India, Guntur, India
Online Conference
Proceedings of Online Conference on Perovskites for Energy Harvesting: From Fundamentals to Devices (PERENHAR)
Online, Spain, 2020 November 19th - 20th
Organizers: Dinesh Kabra, Sandheep Ravishankar, Angshuman Nag and Priya Mahadevan
Poster, Kunchanapalli Ramya, 058
Publication date: 2nd November 2020
ePoster: 

Halide Perovskites (HaPs; having a general structural formula of ABX3; where A is the monovalent cation-methyl ammonium-MA/Cesium-Cs+, B is the lead-Pb2+ and X is the halide species-I-/Br-/Cl-) act as emerging candidates in the future optoelectronic technology with their high photo conversion efficiency (PCE) over 25%. Furthermore, HaPs demonstrate tunable bandgap, high carrier diffusion length, long carrier lifetime, low defect density, and efficient charge collection at metal electrodes beneficial for excellent device application. We report in-situ, room-temperature synthesis of methylammonium lead bromide (MAPbBr3) crystals using N-methyl formamide (NMF) as a solvent to understand their structural, electronic, and dielectric properties. The elemental analysis and improvement in the thermal stability of the synthesized MAPbBr3 crystals were examined with X-ray diffraction (XRD) and Thermo Gravimetric Analysis (TGA) analysis. Two-step thermal degradation was observed at ~3500C and ~5500C respectively. In the first step nearly 3500C, there is defragmentation of organic cation that occurs, which fragments crystals as methylamine (CH3NH2) and hydrobromic acid (HBr). In the second thermal degradation process at ~5500C, we observed complete defragmentation of the perovskite crystal structure. The optical properties of MAPbBr3 crystals depict a sharp rise in the absorbance ~ 570 nm regime which confirms the presence of direct bandgap material in the crystals. Dielectrics and electrical transport properties of these crystals were inspected using impedance spectroscopy tool for various applied AC voltages ranging from 10 mV to 500 mV. Equivalent circuits for the Nyquist plots i.e., Im(Z) vs Re (Z) were found wherein two different circuit parameters were obtained for 10-50 mV range and 100-500 mV AC voltage range respectively. Using simple capacitor frequency relation, we obtained the average relative permittivity of crystals of ~ 60.

In conclusion, the synthesized MAPbBr3 crystals showed high thermal and structural stabilities with a higher value of dielectric constant. Impedance spectroscopy measurements were performed under various applied AC voltages to optimize the AC voltage for device operation and to understand the change in electrical transport behaviors of the synthesized MAPbBr3 crystals. 

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