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- Liu, Lige, et al.
(författare)
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Cation effect on excitons in perovskite nanocrystals from single-dot photoluminescence of CH3NH3PbI3
- 2019
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 100:19
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Tidskriftsartikel (refereegranskat)abstract
- The single-dot photoluminescence properties of similar to 7 nm perovskite MAPbI(3) (MA = CH3NH3+) nanocrystals (NCs) were investigated in the 5-295 K temperature range both in spectral and time domains. Repeatable single-dot measurements were facilitated by the use of a protective polymer, which stabilized the NCs. Temperature-induced phase transition and exciton-phonon interactions were revealed as well as the exciton fine structure. A pronounced spectral jump of the emission peak at 140-160 K, indicating a tetragonal-orthorhombic phase transition, was observed. In addition, the emission linewidth of similar to 0.6 meV was measured, which is the narrowest ever recorded for this perovskite material system. A similar to 4.0 meV phonon mode was identified for the NCs at 5 K, defining the linewidth thermal broadening. In general, the presence of MA(+) leads to broader spectra than for Cs+ or FA(+) containing perovskite NCs. It is attributed to higher polarity of this cation, thus it is more susceptible to spectral diffusion, which is clearly observed here. Photoluminescence decay measurements indicated that the recombination from the lowest energy state of the emission level manifold is partially forbidden. This is opposite to Cs+ cation NCs, highlighting the central role of the positive ion in the exchange interaction in perovskites. Finally, delayed luminescence was found to govern the recombination dynamics below room temperature, suggesting an involvement of trap sites for the orthorhombic phase. The reported photophysics of a quantum-confined exciton in this material, which is of interest for various light-converting applications, clarifies the role of the cation in perovskite nanocrystal optical properties.
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| 2. |
- Liu, Lige, et al.
(författare)
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Size-Dependent Phase Transition in Perovskite Nanocrystals
- 2019
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 10:18, s. 5451-5457
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Tidskriftsartikel (refereegranskat)abstract
- Organic-inorganic hybrid perovskites simultaneously possess strong spin- orbit coupling (SOC) and structure inversion asymmetry, establishing a Rashba effect to influence light emission and photovoltaics. Here, we use mechanical bending as a convenient approach to investigate the Rashba effect through SOC in perovskite (MAPbI(3-x)Cl(x)) films by elastically deforming grains. It is observed that applying a concave bending can broaden the line shape of the magnetophotocurrent, increasing the internal magnetic parameter B-0 from 121 to 205 mT, which indicates an enhancement on SOC. Interestingly, the PL lifetime is found to be enlarged from 9.9 to 14.8 ns under this bending, which suggests that introducing compressive strain can essentially increase the Rashba effect through SOC, leading to an increase upon indirect band transition. Furthermore, the PL peak associated with the Rashba effect is shifted from 776 to 780 nm under this mechanical bending. Therefore, mechanical bending provides a convenient experimental method to approach the Rashba effect in hybrid perovskites.
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