| 1. |
- Rehermann, Carolin, et al.
(författare)
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Origin of Ionic Inhomogeneity in MAPb(IxBr1-x)3Perovskite Thin Films Revealed by In-Situ Spectroscopy during Spin Coating and Annealing
- 2020
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 12:27, s. 30343-30352
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Tidskriftsartikel (refereegranskat)abstract
- Irradiation-induced phase segregation in mixed methylammonium halide perovskite samples such as methylammonium lead bromide-iodide, MAPb(IxBr1-x)3, is being studied intensively because it limits the efficiency of wide band gap perovskite solar cells. It has been postulated that this phenomenon depends on the intrinsic ionic (in)homogeneity in samples already induced during film formation. A deeper understanding of the MAPb(IxBr1-x)3 formation processes and the influence of the halide ratio, solvents, and the perovskite precursor composition as well as the influence of processing parameters during deposition, e.g., spin coating and annealing parameters, is still lacking. Here, we use a fiber optic-based optical in-situ setup to study the formation processes of the MAPb(IxBr1-x)3 series on a subsecond time scale during spin coating and thermal annealing. In-situ UV-vis measurements during spin coating reveal the influence of different halide ratios, x, in the precursor solution on the preferential crystallization of the phase. Pure bromide samples directly form a perovskite phase, samples with high iodide content form a solvate intermediate phase, and samples with a mixed stoichiometry between 0.1 ≤ x ≤ 0.6 form both. This leads to a heterogeneous formation process via two competing reaction pathways, that leads to a heterogeneous mixture of phases, during spin coating and rationalizes the compositional heterogeneity of mixed bromide-iodide samples even after annealing.
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| 2. |
- Suchan, Klara, et al.
(författare)
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Complex evolution of photoluminescence during phase segregation of MAPb(I1-xBrx)3 mixed halide perovskite
- 2020
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 221
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Tidskriftsartikel (refereegranskat)abstract
- Under illumination, the photoluminescence of a mixed-halide perovskite such as MAPb(I1-xBrx)3 is known to undergo a significant intensity enhancement while spectrally shifting to lower energies. The evolution of low energy photoluminescence is attributed to the formation of iodide rich domains due to phase segregation. This process is detrimental for optoelectronic devices however the mechanism is not well-understood. Here we present a real-time study of the photoluminescence evolution in MAPb(I1-xBrx)3 samples during light-induced phase segregation. We show that the evolution of photoluminescence proceeds via several intermediate stages making it more complex than previously suggested. Within the first few seconds of photo-excitation, we found a very rapid formation of a short-lived intense photoluminescence band with a peak energy even lower than the final emission of the fully segregated sample. We propose that this emission comes from small pure iodide nano-domains formed during the initial stage of photo-induced phase-segregation.
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| 3. |
- Suchan, Klara
(författare)
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Life and Death of Mixed Metal Halide Perovskites : Mechanism and Consequences of Light Induced Halide Segregation in MAPb(I,Br)3
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Metal halide perovskites have attracted immense scientific interest due to their outstanding optoelectronic properties over a widebandgap range. Applications cover a wide range of optoelectronic devices from solar cells, LEDs and lasers to X-ray detectors.[1,2] Particularly in combination with existing silicon technology, perovskite-silicon tandem solar cells, which achieve power conver-sion efficiencies of over 32 %, have the potential to reduce the effective cost of solar cell devices, making them economically viableover carbon-based energy generation.[1] Despite tremendous efforts, the reliable and stable operation of metal halide perovskitesis still hindered by dynamic phenomena such as current-voltage hysteresis,[3, 4] dynamic defect formation,[5, 6] degradation andlight-induced phase segregation.[7] The high ion mobility of metal halide perovskites has been proposed to be at the core of thesecritical instabilities that prevent commercial application. Ion mobility is known to be enhanced under illumination. However, insingle halide systems it is not trivial to detect ion migration. Mixed halide systems therefore provide a unique model system formonitoring ion migration due to the formation of distinctly different phases under illumination. This provides a unique oppor-tunity to gain further insight into the relationship between optical excitation and ion migration.This thesis investigates the phase segregation that occurs upon optical illumination of metal halide perovskites with mixed halides(bromide and iodide).In a meta-data study, we analyze over 45 000 solar cell device metrics to explore the contribution of phase segregation to deviceperformance.Furthermore, we analyze the mechanism of phase segregation. In this work, we present insights from photoluminescence mi-croscopy as well as multimodal photoluminescence and X-ray diffraction measurements of the temperature and compositiondependence of phase segregation. We revealed the complexity of the phase segregation process and proposed an alternative kineticmodel to rationalize the entire process.In addition, we described the X-ray sensitivity of mixed metal halide perovskites and the challenges encountered when using X-ray-based characterization techniques. In particular, we discovered that X-ray induced defects can alter the photo-stability of metalhalide perovskites, making meaningful characterization of the phase segregation process very complex.Our results highlight the complex interplay between ion mobility, photostability, and photon-induced defects. We are confidentthat these insights will contribute to a detailed understanding of light-induced phase segregation and ion migration in general. Wehope that this understanding will point the way to stable and reliable operation of metal halide perovskite solar cells.
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| 4. |
- 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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| 5. |
- Suchan, Klara, et al.
(författare)
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Optical : In situ monitoring during the synthesis of halide perovskite solar cells reveals formation kinetics and evolution of optoelectronic properties
- 2020
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 8:20, s. 10439-10449
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Tidskriftsartikel (refereegranskat)abstract
- The formation mechanism and the evolution of optoelectronic properties during annealing of chlorine-derived methylammonium lead iodide (MAPbI3-xClx) are investigated in detail combining in situ and ex situ optical and structural characterization. Using in situ optical reflectometry we are able to monitor the evolution of the MAPbI3-xClx phase as a function of time and processing temperature. The formation kinetics is fitted using an improved Johnson-Mehl-Avrami-Kolmogorov model and a delayed formation of MAPbI3-xClx is found when chlorine is present in the precursor. This is verified by X-ray diffraction and X-ray fluorescence measurements. From absolute photoluminescence measurements we determine the implied Voc during film formation, which exhibits a maximum at a specific time during the annealing process. In conjunction with ex situ time-resolved photoluminescence we deduce a decrease in the net doping density for increased annealing times, while the minority carrier lifetime stays constant. We thus demonstrate the potential of in situ optical spectroscopy to monitor and tailor the electronic properties of hybrid perovskites directly during film growth, which can be easily applied to different growth recipes and synthesis environments.
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| 6. |
- Suchan, Klara, et al.
(författare)
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Rationalizing Performance Losses of Wide Bandgap Perovskite Solar Cells Evident in Data from the Perovskite Database
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Ingår i: Advanced Energy Materials. - 1614-6832.
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Tidskriftsartikel (refereegranskat)abstract
- Metal halide perovskites (MHPs) have become a widely studied class of semiconductors for various optoelectronic devices. The possibility to tune their bandgap (Eg) over a broad spectral range from 1.2 eV to 3 eV by compositional engineering makes them particularly attractive for light emitting devices and multi-junction solar cells. In this metadata study, data from Peer-reviewed publications available in the Perovskite Database (www.perovskitedatabase.com) is used to evaluate the current state of Eg tuning in wide Eg MHP semiconductors. Recent literature on wide Eg MHP semiconductors is examined and the data is extracted and uploaded onto the Perovskite Database. Beyond describing recent highlights and scientific breakthroughs, general trends are drawn from 45,000 individual experimental datasets of MHP solar cell devices. The historical evolution of MHP solar cells is recapitulated, and general conclusions are drawn about the current limits of device performance. Three dominant causes are identified and discussed for the degradation of performance relative to the Shockley-Queisser (SQ) model's theoretical limit for single-junction solar cells: 1) energetically mismatched selective transport materials for wide Eg MHPs, 2) lower optoelectronic quality of wide Eg MHP absorbers, and 3) dynamically evolving compositional heterogeneity due to light-induced phase segregation phenomena.
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| 7. |
- Zhang, Zhaojun, et al.
(författare)
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Vertically Aligned CsPbBr3 Nanowire Arrays with Template-Induced Crystal Phase Transition and Stability
- 2021
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:8, s. 4860-4868
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Tidskriftsartikel (refereegranskat)abstract
- Metal halide perovskites show great promise for a wide range of optoelectronic applications but are plagued by instability when exposed to air and light. This work presents low-temperature solution growth of vertically aligned CsPbBr3 nanowire arrays in AAO (anodized aluminum oxide) templates with excellent stability, with samples exposed to air for 4 months still exhibiting comparable photoluminescence and UV stability to fresh samples. The single-crystal nanowire length is adjusted from ∼100 nm to 5 μm by adjusting the precursor solution amount and concentration, and we observe length-to-diameter ratios as high as 100. Structural characterization results indicate that large-diameter CsPbBr3 nanowires have an orthorhombic structure, while the 10 nm- and 20 nm-diameter nanowires adopt a cubic structure. Photoluminescence shows a gradual blue-shift in emission with decreasing nanowire diameter and marginal changes under varying illumination power intensity. The CsPbBr3-nanowires/AAO composite exhibits excellent resistance to X-ray radiation and long-term air storage, which makes it promising for future optoelectronic applications such as X-ray scintillators. These results show how physical confinement in AAO can be used to realize CsPbBr3 nanowire arrays and control their morphology and crystal structure.
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