| 1. |
- Eremchev, Ivan Yu, et al.
(författare)
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Detection of Single Charge Trapping Defects in Semiconductor Particles by Evaluating Photon Antibunching in Delayed Photoluminescence
- 2023
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992.
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Tidskriftsartikel (refereegranskat)abstract
- Time-resolved analysis of photon cross-correlation function g(2)(τ) is applied to photoluminescence (PL) of individual submicrometer size MAPbI3 perovskite crystals. Surprisingly, an antibunching effect in the long-living tail of PL is observed, while the prompt PL obeys the photon statistics typical for a classical emitter. We propose that antibunched photons from the PL decay tail originate from radiative recombination of detrapped charge carriers which were initially captured by a very limited number (down to one) of shallow defect states. The concentration of these trapping sites is estimated to be in the range 1013-1016 cm-3. In principle, photon correlations can be also caused by highly nonlinear Auger recombination processes; however, in our case it requires unrealistically large Auger recombination coefficients. The potential of the time-resolved g(2)(0) for unambiguous identification of charge rerecombination processes in semiconductors considering the actual number of charge carries and defects states per particle is demonstrated.
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| 2. |
- Bartholomew, John G., et al.
(författare)
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High-resolution spectroscopic techniques for studying rare-earth ions in nanoparticles
- 2023
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 257
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Tidskriftsartikel (refereegranskat)abstract
- Rare-earth doped nanoparticles can exhibit narrow optical and spin linewidths at low temperatures. These outstanding properties for nanomaterials make them attractive for quantum technologies based on optically addressable spins such as quantum memories and computers. Although accurate linewidth measurements have been reported using, for example, spectral hole burning or photon echo techniques, so far they have been mostly restricted to large ensembles of particles. Being able to extend linewidths measurements to few and single particles is particularly important in view of their integration in nanophotonic devices. In this paper, we present techniques for determining inhomogeneous and homogeneous linewidths of small ensembles of rare-earth ions in doped nanoparticles with high signal-to-noise ratios for convenient integration times. Using these techniques we have observed property variations for particles from the same synthesis, a first step towards their optimization for applications in quantum technologies.
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| 3. |
- 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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| 4. |
- Goetz, Katelyn P., et al.
(författare)
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Remarkable performance recovery in highly defective perovskite solar cells by photo-oxidation
- 2023
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 11:24, s. 8007-8017
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Tidskriftsartikel (refereegranskat)abstract
- Exposure to environmental factors is generally expected to cause degradation in perovskite films and solar cells. Herein, we show that films with certain defect profiles can display the opposite effect, healing upon exposure to oxygen under illumination. We tune the iodine content of methylammonium lead triiodide perovskite from understoichiometric to overstoichiometric and expose them to oxygen and light prior to the addition of the top layers of the device, thereby examining the defect dependence of their photooxidative response in the absence of storage-related chemical processes. The contrast between the photovoltaic properties of the cells with different defects is stark. Understoichiometric samples indeed degrade, demonstrating performance at 33% of their untreated counterparts, while stoichiometric samples maintain their performance levels. Surprisingly, overstoichiometric samples, which show low current density and strong reverse hysteresis when untreated, heal to maximum performance levels (the same as untreated, stoichiometric samples) upon the photooxidative treatment. A similar, albeit smaller-scale, effect is observed for triple cation and methylammonium-free compositions, demonstrating the general application of this treatment to state-of-the-art compositions. We examine the reasons behind this response by a suite of characterization techniques, finding that the performance changes coincide with microstructural decay at the crystal surface, reorientation of the bulk crystal structure for the understoichiometric cells, and a decrease in the iodine-to-lead ratio of all films. These results indicate that defect engineering is a powerful tool to manipulate the stability of perovskite solar cells.
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| 5. |
- Kharintsev, Sergey S., et al.
(författare)
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Light-Controlled Multiphase Structuring of Perovskite Crystal Enabled by Thermoplasmonic Metasurface
- 2023
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 17:10, s. 9235-9244
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Tidskriftsartikel (refereegranskat)abstract
- Halide perovskites belong to an important family of semiconducting materials with electronic properties that enable a myriad of applications, especially in photovoltaics and optoelectronics. Their optical properties, including photoluminescence quantum yield, are affected and notably enhanced at crystal imperfections where the symmetry is broken and the density of states increases. These lattice distortions can be introduced through structural phase transitions, allowing charge gradients to appear near the interfaces between phase structures. In this work, we demonstrate controlled multiphase structuring in a single perovskite crystal. The concept uses cesium lead bromine (CsPbBr3) placed on a thermoplasmonic TiN/Si metasurface and enables single-, double-, and triple-phase structures to form on demand above room temperature. This approach promises application horizons of dynamically controlled heterostructures with distinctive electronic and enhanced optical properties.
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| 6. |
- Lamers, Nils, et al.
(författare)
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Gas-Phase Anion Exchange for Multisegment Heterostructured CsPb(Br1−xClx)3 Perovskite Nanowires
- 2023
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Ingår i: Advanced Optical Materials. - 2195-1071.
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Tidskriftsartikel (refereegranskat)abstract
- Metal-halide perovskites (MHPs) are promising as active optoelectronic materials for a diverse range of devices. Anion exchange is a post-growth modification of MHP materials that allows tuning of the band gap and crystal structure by exposure to alternative halides, normally using solution methods. Here, low temperature gas-phase anion exchange for the conversion of CsPbBr3 nanowires (NW) into CsPb(Br1−xClx) NWs using two media, fuming HCl and Cl2 gas, is systematically investigated. It is found that both methods can be used to tune the composition in the full range with excellent control. While fuming HCl is the simplest process, Cl2 gives similar results with no surface damage and better process control. Based on a simple solid diffusion model, an average diffusivity of 1.4 × 10−12 cm2s−1 is extracted for Cl-anions inside CsPbBr3. By combining the Cl2 exchange process with electron-beam lithography patterning, heterojunction NWs with varying halide compositions are produced, including complex barcode-like NWs with segment lengths as short as 500 nm. Designed heterostructures provide an important basis for optoelectronic device applications of MHPs, and gas-phase anion exchange should be suitable for any MHP morphology.
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| 7. |
- Liang, Mingli, et al.
(författare)
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Spatially Resolved Local Electronic Properties of 2D Lead Halide Perovskite Single Crystals Studied by X-Ray Photoemission Electron Microscopy
- 2023
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Ingår i: Solar RRL. - : Wiley. - 2367-198X. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- Recently, research on the edge states of 2D lead halide perovskites (LHPs) has been attracting much attention. The lower-energy edge state (LES) is believed to provide an efficient pathway for the dissociation of photoexcited excitons. However, the mechanism of the LES formation remains controversial, and studies that establish precisely the local electronic properties are lacking. Herein, the first study of spatially resolved electronic structures in 2D LHP single-crystal flakes by X-ray photoemission electron microscopy is presented, specifically identifying the contribution from the edge area. The results show that blueshifts occur in the Pb 5d core-level peaks at the edge area compared to the interior area with much less difference in I 4d core-level peaks. The shift becomes more pronounced as n varies from 1 to 3 (≈0.2–1.0 eV). This phenomenon is attributed to the surface restructuring of the edge area induced by the release of mechanical strain through lattice expansion. This work provides an important reference on the origin of the LES of 2D LHPs and is beneficial for future optoelectronic device applications.
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| 8. |
- Louis, Boris, et al.
(författare)
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Unravelling 3D Dynamics and Hydrodynamics during Incorporation of Dielectric Particles to an Optical Trapping Site
- 2023
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 17:4, s. 3797-3808
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Tidskriftsartikel (refereegranskat)abstract
- Mapping of the spatial and temporal motion of particles inside an optical field is critical for understanding and further improvement of the 3D spatio-temporal control over their optical trapping dynamics. However, it is not trivial to capture the 3D motion, and most imaging systems only capture a 2D projection of the 3D motion, in which the information about the axial movement is not directly available. In this work, we resolve the 3D incorporation trajectories of 200 nm fluorescent polystyrene particles in an optical trapping site under different optical experimental conditions using a recently developed widefield multiplane microscope (imaging volume of 50 × 50 × 4 μm3). The particles are gathered at the focus following some preferential 3D channels that show a shallow cone distribution. We demonstrate that the radial and the axial flow speed components depend on the axial distance from the focus, which is directly related to the scattering/gradient optical forces. While particle velocities and trajectories are mainly determined by the trapping laser profile, they cannot be completely explained without considering collective effects resulting from hydrodynamic forces.
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| 9. |
- Suchan, Klara, et al.
(författare)
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Multi-Stage Phase-Segregation of Mixed Halide Perovskites under Illumination : A Quantitative Comparison of Experimental Observations and Thermodynamic Models
- 2023
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Ingår i: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 33:3
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Tidskriftsartikel (refereegranskat)abstract
- Photo- and charge-carrier-induced ion migration is a major challenge when utilizing metal halide perovskite semiconductors for optoelectronic applications. For mixed iodide/bromide perovskites, the compositional instability due to light- or electrical bias induced phase-segregation restricts the exploitation of the entire bandgap range. Previous experimental and theoretical work suggests that excited states or charge carriers trigger the process, but the exact mechanism is still under debate. To identify the mechanism and cause of light-induced phase-segregation phenomena, the full compositional range of methylammonium lead bromide/iodide samples are investigated, MAPb(BrxI1-x)3 with x = 0…1, by simultaneous in situ X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy during illumination. The quantitative comparison of composition-dependent in situ XRD and PL shows that at excitation densities of 1 sun, only the initial stage of photo-segregation is rationalized with the previously established thermodynamic models. However, a progression of the phase segregation is observed that is rationalized by considering long-lived accumulative photo-induced material alterations. It is suggested that (additional) photo-induced defects, possibly halide vacancies and interstitials, need to be considered to fully rationalize light-induced phase segregation and anticipate the findings to provide crucial insight for the development of more sophisticated models.
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| 10. |
- Wan, Sushu, et al.
(författare)
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All-Optical Switching Based on Sub-Bandgap Photoactivation of Charge Trapping in Metal Halide Perovskites
- 2023
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 35:13
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Tidskriftsartikel (refereegranskat)abstract
- Controllable optical properties are crucial for the application of light-emitting materials in optical devices. In this work, controllable photoluminescence in metal halide perovskite crystals is realized via photoactivation of their defects. It is found that under continuous excitation, the photoluminescence intensity of a CH3NH3PbBr3 crystal can be fully controlled by sub-bandgap energy photon illumination. Such optically controllable emission behavior is rather general as it is observed also in CsPbBr3 and other perovskite materials. The switching mechanism is assigned to reversible light-induced activation/deactivation of nonradiative recombination centers, the presence of which relates to an excess of Pb during perovskite synthesis. Given the success of perovskites in photovoltaics and optoelectronics, it is believed that the discovery of green luminescence controlled by red illumination will extend the application scope of perovskites toward optical devices and intelligent control.
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