| 1. |
- Seth, Sudipta, et al.
(författare)
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Presence of Maximal Characteristic Time in Photoluminescence Blinking of MAPbI3 Perovskite
- 2021
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Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6832 .- 1614-6840. ; 11:44
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Tidskriftsartikel (refereegranskat)abstract
- Photoluminescence (PL) blinking is a common phenomenon in nanostructured semiconductors associated with charge trapping and defect dynamics. PL blinking kinetics exhibit very broadly distributed timescales. The traditionally employed analysis of probability distribution of ON and OFF events suffers from ambiguities in their determination in complex PL traces making its suitability questionable. Here, the statistically correct power spectral density (PSD) estimation method applicable for fluctuations of any complexity is employed. PSDs of the blinking traces of submicrometer MAPbI3 crystals at high frequencies follow power law with excitation power density dependent parameters. However, at frequencies less than 0.3 Hz, the majority of the PSDs saturate revealing the presence of a maximal characteristic timescale of blinking in the range of 0.5–10 s independently of the excitation power density. Super-resolution optical microscopy shows the characteristic timescale to be an inherent material property independent of polycrystallinity. Thus, for the first time the maximum timescale of the multiscale blinking behavior of nanoparticles is observed demonstrating that the power law statistics are not universal for semiconductors. It is proposed that the viscoelasticity of metal-halide perovskites can limit the maximum timescale for the PL fluctuations by limiting the memory of preceded deformations/re-arrangements of the crystal lattice.
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| 2. |
- Galle, Marco H.J.J., et al.
(författare)
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Self-Healing Ability of Perovskites Observed via Photoluminescence Response on Nanoscale Local Forces and Mechanical Damage
- 2023
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Ingår i: Advanced Science. - : Wiley. - 2198-3844. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- The photoluminescence (PL) of metal halide perovskites can recover after light or current-induced degradation. This self-healing ability is tested by acting mechanically on MAPbI3 polycrystalline microcrystals by an atomic force microscope tip (applying force, scratching, and cutting) while monitoring the PL. Although strain and crystal damage induce strong PL quenching, the initial balance between radiative and nonradiative processes in the microcrystals is restored within a few minutes. The stepwise quenching–recovery cycles induced by the mechanical action is interpreted as a modulation of the PL blinking behavior. This study proposes that the dynamic equilibrium between active and inactive states of the metastable nonradiative recombination centers causing blinking is perturbed by strain. Reversible stochastic transformation of several nonradiative centers per microcrystal under application/release of the local stress can lead to the observed PL quenching and recovery. Fitting the experimental PL trajectories by a phenomenological model based on viscoelasticity provides a characteristic time of strain relaxation in MAPbI3 on the order of 10–100 s. The key role of metastable defect states in nonradiative losses and in the self-healing properties of perovskites is suggested.
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| 3. |
- Gerhard, Marina, et al.
(författare)
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Heterogeneities and Emissive Defects in MAPbI3 Perovskite Revealed by Spectrally Resolved Luminescence Blinking
- 2021
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Ingår i: Advanced Optical Materials. - : Wiley. - 2195-1071. ; 9:18
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Tidskriftsartikel (refereegranskat)abstract
- The fate of excited charge carriers in metal halide perovskite semiconductors is influenced by energetic disorder and defects. Here, photoluminescence (PL) blinking is used to probe metastable nonradiative (NR) centers and the nanoscale energy landscape. Temporal activation of an NR center creates a local region with increased NR recombination. Activation and deactivation of this local PL quenching does not only lead to PL blinking, but also to fluctuations of the PL spectra, if the crystal is inhomogeneous in the sense that the PL emission spectrum is slightly different from one location to another. It resembles the spectral hole-burning technique; however, here the eliminated excited states are chosen by their spatial localization close to the quencher. In MAPbI3, PL spectral fluctuations at low temperature reveal energetic inhomogeneities on the order of 5 to 10 meV. Quenching of the main PL band is often found to correlate with an increase of the low-energetic tail of the PL spectra, which is attributed to partially radiative recombination of charges captured by the NR center. The transition energy of the NR center is found to be only ≈80 meV smaller than the bandgap, implying that the underlying defect cannot be a single mid-bandgap state.
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| 4. |
- Kiligaridis, Alexander, et al.
(författare)
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Are Shockley-Read-Hall and ABC models valid for lead halide perovskites?
- 2021
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Metal halide perovskites are an important class of emerging semiconductors. Their charge carrier dynamics is poorly understood due to limited knowledge of defect physics and charge carrier recombination mechanisms. Nevertheless, classical ABC and Shockley-Read-Hall (SRH) models are ubiquitously applied to perovskites without considering their validity. Herein, an advanced technique mapping photoluminescence quantum yield (PLQY) as a function of both the excitation pulse energy and repetition frequency is developed and employed to examine the validity of these models. While ABC and SRH fail to explain the charge dynamics in a broad range of conditions, the addition of Auger recombination and trapping to the SRH model enables a quantitative fitting of PLQY maps and low-power PL decay kinetics, and extracting trap concentrations and efficacies. However, PL kinetics at high power are too fast and cannot be explained. The proposed PLQY mapping technique is ideal for a comprehensive testing of theories and applicable to any semiconductor.
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| 5. |
- Shi, Juanzi, et al.
(författare)
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Photoluminescence Polarization of MAPbBr3 Perovskite Nanostructures. Can the Dielectric Contrast Effect Explain It?
- 2022
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 9:12, s. 3888-3898
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Tidskriftsartikel (refereegranskat)abstract
- The dielectric contrast effect is usually evoked to explain anisotropy of optical properties of elongated nanoobjects, for example, semiconductor nanowires. We applied two-dimensional polarization imaging microscopy to measure the polarization of photoluminescence (PL) excitation and PL intensity of nanoaggregates of in-situ formed MAPbBr3perovskite nanoparticles in a stretched polymeric matrix. Scanning electron microscopy images of these objects were also acquired to characterize their sizes and shapes. We find that individual perovskite aggregates with sizes of 100-300 nm often possess a PL excitation polarization degree as high as 0.5-0.9, which is up to three times higher than the polarization degree of absorption predicted by the dielectric contrast effect. Small aggregates of nanoparticles possess an emission polarization degree substantially higher than that of excitation. Computer simulations of many possible scenarios show that the dielectric contrast alone cannot quantitatively explain the polarization properties of the studied objects. We propose energy transfer to localized emitting sites and the dependence of PL yield on excitation power density as possible factors strongly influencing the polarization properties of PL emission and PL excitation, respectively.
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