Behavior of Methylammonium Dipoles in MAPbX(3) (X = Br and I)

Govinda, Sharada and Kore, Bhushan P and Bokdam, Menno and Mahale, Pratibha and Kumar, Abhinav and Pal, Somnath and Bhattacharyya, Biswajit and Lahnsteiner, Jonathan and Kresse, Georg and Franchini, Cesare and Pandey, Anshu and Sarma, D D (2017) Behavior of Methylammonium Dipoles in MAPbX(3) (X = Br and I). In: JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 8 (17). pp. 4113-4121.

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Abstract

Dielectric constants of MAPbX(3) (X = Br, I) in the 1 kHz-1 MHz range show strong temperature dependence near room temperature, in contrast to the nearly temperature -independent dielectric constant of CsPbBr3. This strong temperature dependence for MAPbX(3) in the tetragonal phase is attributed to the MA+ dipoles rotating freely within the probing time scale. This interpretation is supported by ab initio molecular dynamics simulations on MAPbI(3) that establish these dipoles as randomly oriented with a rotational relaxation time scale of similar to 7 ps at 300 K. Further, we probe the intriguing possibility of transient polarization of these dipoles following a photo excitation process with important consequences on the photovoltaic efficiency, using a photoexcitation pump and second harmonic generation efficiency as a probe with delay times spanning 100 fs-1.8 ns. The absence of a second harmonic signal at any delay time rules out the possibility of any transient ferroelectric state under photoexcitation.

Item Type:	Journal Article
Publication:	JOURNAL OF PHYSICAL CHEMISTRY LETTERS
Additional Information:	Copy right for this article belongs to the AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited:	07 Oct 2017 06:07
Last Modified:	07 Oct 2017 06:07
URI:	http://eprints.iisc.ac.in/id/eprint/57979

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