Phase Diagram and Dielectric Property of MA(1-x)FA(x)PbI3 through Impedance Spectroscopy
Ashutosh Mohanty a, Diptikanta Swain a, Sharada Govinda a, Tayur N. Guru Row a, D. D. Sarma a
a Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, India
Proceedings of International Conference on Impedance Spectroscopy and Related Techniques in Metal Halide Perovskites (PERIMPED)
Online, Spain, 2020 October 6th - 7th
Organizers: Juan Bisquert, Bruno Ehrler and Eline Hutter
Oral, Ashutosh Mohanty, presentation 017
Publication date: 25th September 2020

The perovskite materials with ABX3 structure, where A = organic cation, B = inorganic cation and X = halides, are commonly known as Organic-Inorganic Hybrid Perovskite. In this regard, FAPbI3 and MAPbI3 (FA = NH2CHNH2 cation and MA = CH3NH3 cation) with perovskite structures are excellent solar absorber materials and potential candidates for the future photovoltaic applications. However, at ambient temperature the stability is a matter of concern for these materials as FAPbI3 transforms to a non-perovskite phase which is a bad solar absorbent and MAPbI3 decomposes with time. In this connection, it is found that the solid solutions of FAPbI3 and MAPbI3 are more stable in comparison to their individual phases. Thus, we have carried out a thorough investigation of the crystal phases of the solid solution i.e. MA(1-x)_FA(x)_PbI3 system for various x values at different temperatures covering 300 K down to 15 K by using variable temperature powder X-ray diffraction (XRD) measurement. The obtained space groups at different crystal phases are confirmed by temperature dependent single crystal XRD. In total, four crystallographic phases exist for this solid solution series namely, cubic, tetragonal, large-cell cubic and orthorhombic. By performing variable temperature dielectric measurement in impedance spectrometer, we have also seen that the dielectric constant correlates strongly with the structure. Therefore, properties of such doped systems, known to be essential for high efficiency together with stability, will have to be understood in terms of their crystallographic phases, which will be discussed in detail in the present work.

A.M. thanks University Grant Commission (UGC), Govt. of India for senior research fellowship. D.D.S. thanks Jamsetji Tata Trust for chair professorship.

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