Dielectric Property Correlates with Structure in Mixed Cation Lead Iodide
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 (SSCU), Indian Institute of Science, IN, Bangalore, Bengaluru, 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, Ashutosh Mohanty, 076
Publication date: 2nd November 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, 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 we are discussing in detail in the present work.

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