期刊
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
卷 9, 期 4, 页码 895-901出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpclett.7b03296
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资金
- Royal Society [UF1402310, RG160046]
- PVTEAM programme grant - Engineering and Physical Sciences Research Council [EP/L017792/1]
- BCFN [EP/G036780/1]
- EPSRC DTA
- STFC [16230050]
- Engineering and Physical Sciences Research Council [1668285, EP/L017792/1] Funding Source: researchfish
- BBSRC [BB/L014335/1] Funding Source: UKRI
- EPSRC [EP/L017792/1] Funding Source: UKRI
Organic cation rotation in hybrid organic-inorganic lead halide perovskites has previously been associated with low charge recombination rates and (anti)ferroelectric domain formation. Two-dimensional infrared spectroscopy (2DIR) was used to directly measure 470 +/- 50 fs and 2.8 +/- 0.5 ps time constants associated with the reorientation of formamidinium cations (FA(+), NH2CHNH2+) in formamidinium lead iodide perovskite thin films. Molecular dynamics simulations reveal the FA(+) agitates about an equilibrium position, with NH2 groups pointing at opposite faces of the inorganic lattice cube, and undergoes 90 degrees flips on picosecond time scales. Time-resolved infrared measurements revealed a prominent vibrational transient feature arising from a vibrational Stark shift: photogenerated charge carriers increase the internal electric field of perovskite thin films, perturbing the FA(+) antisymmetric stretching vibrational potential, resulting in an observed 5 cm(-1) shift. Our 2DIR results provide the first direct measurement of FA(+) rotation inside thin perovskite films, and cast significant doubt on the presence of long-lived (anti)ferroelectric domains, which the observed low charge recombination rates have been attributed to.
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