TY - JOUR
T1 - Behavior of Methylammonium Dipoles in MAPbX3 (X = Br and I)
AU - Govinda, Sharada
AU - Kore, Bhushan P.
AU - Bokdam, Menno
AU - Mahale, Pratibha
AU - Kumar, Abhinav
AU - Pal, Somnath
AU - Bhattacharyya, Biswajit
AU - Lahnsteiner, Jonathan
AU - Kresse, Georg
AU - Franchini, Cesare
AU - Pandey, Anshu
AU - Sarma, D. D.
N1 - Funding Information:
The authors thank the Department of Science and Technology, Government of India for support and Mr. Guru Pratheep. R. for help with SHG measurements. S.G. thanks Dr. Sumanta Mukherjee for useful discussions and acknowledges CSIR for a student fellowship. B.P.K. acknowledge UGC, India for a D.S. Kothari Postdoctoral Fellowship. M.B. and J.L. acknowledge funding by the Austrian Science Fund (FWF): P 30316-N27.
Publisher Copyright:
© 2017 American Chemical Society.
PY - 2017/9/7
Y1 - 2017/9/7
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=85029029650&partnerID=8YFLogxK
U2 - 10.1021/acs.jpclett.7b01740
DO - 10.1021/acs.jpclett.7b01740
M3 - Article
C2 - 28812901
AN - SCOPUS:85029029650
VL - 8
SP - 4113
EP - 4121
JO - Journal of physical chemistry letters
JF - Journal of physical chemistry letters
SN - 1948-7185
IS - 17
ER -