Suppression of phase transitions and glass phase signatures in mixed cation halide perovskites
Mantas Simenas a, Sergejus Balciunas a, Jacob N. Wilson b, Sarunas Svirskas a, Martynas Kinka a, Vidmantas Kalendra a, Anna Gagor c, Daria Szewczyk c, Adam Sieradzki d, Miroslaw Maczka c, Aron Walsh b e, Robertas Grigalaitis a, Juras Banys a
a Faculty of Physics, Vilnius University, Sauletekio 3, 10257 Vilnius, Lithuania
b Thomas Young Centre and Department of Materials, Imperial College London, SW7 2AZ London, UK
c Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Okólna 2, 50-422 Wroclaw, Poland
d Department of Experimental Physics, Wroclaw University of Science and Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland
e Department of Materials Science and Engineering, Yonsei University, 03722 Seoul, Korea
nanoGe Perovskite Conferences
Proceedings of International online conference on Hybrid materials and optoelectronic devices (HYBRIDOE)
Online, Spain, 2020 December 15th - 17th
Organizers: Xueqing Xu, Baomin Xu, Hin-Lap (Angus) Yip and Xinhua Zhong
Oral, Mantas Simenas, presentation 012
Publication date: 4th December 2020

Cation engineering provides a route to control the structure and properties of hybrid halide perovskites, which has resulted in the highest performance solar cells based on mixtures of Cs, methylammonium, and formamidinium. Here, we present a multi-technique experimental and theoretical study of structural phase transitions, structural phases and dipolar dynamics in the mixed methylammonium/dimethylammonium MA1-xDMAxPbBr3 hybrid perovskites (0 ≤ x ≤ 1). Our results demonstrate a significant suppression of the structural phase transitions, enhanced disorder and stabilization of the cubic phase even for a small amount of dimethylammonium cations. As the dimethylammonium concentration approaches the solubility limit in MAPbBr3, we observe the disappearance of the structural phase transitions and indications of a glassy dipolar phase. We also reveal a significant tunability of the dielectric permittivity upon mixing of the molecular cations that arises from frustrated electric dipoles [1]. All these aspects are highly important for understanding and improving the performance and stability of the photoactive phases of perovskite solar cells and associated technologies. We discuss that the observed phase transition suppression and formation of the glassy phase might be more general in the mixed compounds.

This project has been funded by the Research Council of Lithuania (LMTLT) (agreement No. S-MIP-19-4) and by EPSRC (Grant No. EP/K016288/1). AW is supported by a Royal Society University Research Fellowship. We are grateful to the UK Materials and Molecular Modelling Hub for computational resources, which is partially funded by EPSRC (EP/P020194/1).

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