%0 Journal Article %1 doi:10.1021/acs.jpclett.7b01740 %A Govinda, Sharada %A Kore, Bhushan P. %A Bokdam, Menno %A Mahale, Pratibha %A Kumar, Abhinav %A Pal, Somnath %A Bhattacharyya, Biswajit %A Lahnsteiner, Jonathan %A Kresse, Georg %A Franchini, Cesare %A Pandey, Anshu %A Sarma, D. D. %D 2017 %J The Journal of Physical Chemistry Letters %K dipoles perovskite phase structure %N 17 %P 4113-4121 %R 10.1021/acs.jpclett.7b01740 %T Behavior of Methylammonium Dipoles in MAPbX3 (X = Br and I) %U http://dx.doi.org/10.1021/acs.jpclett.7b01740 %V 8 %X 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.

@article{doi:10.1021/acs.jpclett.7b01740, 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. }, added-at = {2017-09-07T16:49:29.000+0200}, author = {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.}, biburl = {https://www.bibsonomy.org/bibtex/214ed9f27ec6c963728ae5ca25fab1380/cgoehler}, description = {Behavior of Methylammonium Dipoles in MAPbX3 (X = Br and I) - acs.jpclett.7b01740}, doi = {10.1021/acs.jpclett.7b01740}, eprint = {http://dx.doi.org/10.1021/acs.jpclett.7b01740}, interhash = {92b61e215af177de3f4f404c8e58703f}, intrahash = {14ed9f27ec6c963728ae5ca25fab1380}, journal = {The Journal of Physical Chemistry Letters}, keywords = {dipoles perovskite phase structure}, note = {PMID: 28812901}, number = 17, pages = {4113-4121}, timestamp = {2017-09-07T16:49:29.000+0200}, title = {Behavior of Methylammonium Dipoles in MAPbX3 (X = Br and I)}, url = {http://dx.doi.org/10.1021/acs.jpclett.7b01740}, volume = 8, year = 2017 }