Dielectric constants of MAPbX3 (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 MAPbX3 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 MAPbI3 that establish these dipoles as randomly oriented with a rotational relaxation time scale of ∼7 ps at 300 K. Further, we probe the intriguing possibility of transient polarization of these dipoles following a photoexcitation 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.

Behavior of Methylammonium Dipoles in MAPbX3 (X = Br and I) / Govinda, Sharada; Kore, Bhushan P.; Bokdam, Menno; Mahale, Pratibha; Kumar, Abhinav; Pal, Somnath; Bhattacharyya, Biswajit; Lahnsteiner, Jonathan; Kresse, Georg; Franchini, Cesare; Pandey, Anshu; Sarma, D.D.*. - In: THE JOURNAL OF PHYSICAL CHEMISTRY LETTERS. - ISSN 1948-7185. - STAMPA. - 8:17(2017), pp. 4113-4121. [10.1021/acs.jpclett.7b01740]

Behavior of Methylammonium Dipoles in MAPbX3 (X = Br and I)

Franchini, Cesare
Membro del Collaboration Group
;
2017

Abstract

Dielectric constants of MAPbX3 (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 MAPbX3 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 MAPbI3 that establish these dipoles as randomly oriented with a rotational relaxation time scale of ∼7 ps at 300 K. Further, we probe the intriguing possibility of transient polarization of these dipoles following a photoexcitation 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.
2017
Behavior of Methylammonium Dipoles in MAPbX3 (X = Br and I) / Govinda, Sharada; Kore, Bhushan P.; Bokdam, Menno; Mahale, Pratibha; Kumar, Abhinav; Pal, Somnath; Bhattacharyya, Biswajit; Lahnsteiner, Jonathan; Kresse, Georg; Franchini, Cesare; Pandey, Anshu; Sarma, D.D.*. - In: THE JOURNAL OF PHYSICAL CHEMISTRY LETTERS. - ISSN 1948-7185. - STAMPA. - 8:17(2017), pp. 4113-4121. [10.1021/acs.jpclett.7b01740]
Govinda, Sharada; Kore, Bhushan P.; Bokdam, Menno; Mahale, Pratibha; Kumar, Abhinav; Pal, Somnath; Bhattacharyya, Biswajit; Lahnsteiner, Jonathan; Kresse, Georg; Franchini, Cesare; Pandey, Anshu; Sarma, D.D.*
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