| 1. |
- Aartsen, M. G., et al.
(författare)
-
Search for Prompt Neutrino Emission from Gamma-Ray Bursts with IceCube
- 2015
-
Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 805:1
-
Tidskriftsartikel (refereegranskat)abstract
- We present constraints derived from a search of four years of IceCube data for a prompt neutrino flux from gammaray bursts (GRBs). A single low-significance neutrino, compatible with the atmospheric neutrino background, was found in coincidence with one of the 506 observed bursts. Although GRBs have been proposed as candidate sources for ultra-high-energy cosmic rays, our limits on the neutrino flux disfavor much of the parameter space for the latest models. We also find that no more than similar to 1% of the recently observed astrophysical neutrino flux consists of prompt emission from GRBs that are potentially observable by existing satellites.
|
|
| 2. |
- Aartsen, M. G., et al.
(författare)
-
Development of a general analysis and unfolding scheme and its application to measure the energy spectrum of atmospheric neutrinos with IceCube
- 2015
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 75:3
-
Tidskriftsartikel (refereegranskat)abstract
- We present the development and application of a generic analysis scheme for the measurement of neutrino spectra with the IceCube detector. This scheme is based on regularized unfolding, preceded by an event selection which uses a Minimum Redundancy Maximum Relevance algorithm to select the relevant variables and a random forest for the classification of events. The analysis has been developed using IceCube data from the 59-string configuration of the detector. 27,771 neutrino candidates were detected in 346 days of livetime. A rejection of 99.9999 % of the atmospheric muon background is achieved. The energy spectrum of the atmospheric neutrino flux is obtained using the TRUEE unfolding program. The unfolded spectrum of atmospheric muon neutrinos covers an energy range from 100 GeV to 1 PeV. Compared to the previous measurement using the detector in the 40-string configuration, the analysis presented here, extends the upper end of the atmospheric neutrino spectrum by more than a factor of two, reaching an energy region that has not been previously accessed by spectral measurements.
|
|
| 3. |
- Jacobsson, Jesper, 1984-, et al.
(författare)
-
An open-access database and analysis tool for perovskite solar cells based on the FAIR data principles
- 2022
-
Ingår i: Nature Energy. - : Springer Nature. - 2058-7546. ; 7:1, s. 107-115
-
Tidskriftsartikel (refereegranskat)abstract
- Large datasets are now ubiquitous as technology enables higher-throughput experiments, but rarely can a research field truly benefit from the research data generated due to inconsistent formatting, undocumented storage or improper dissemination. Here we extract all the meaningful device data from peer-reviewed papers on metal-halide perovskite solar cells published so far and make them available in a database. We collect data from over 42,400 photovoltaic devices with up to 100 parameters per device. We then develop open-source and accessible procedures to analyse the data, providing examples of insights that can be gleaned from the analysis of a large dataset. The database, graphics and analysis tools are made available to the community and will continue to evolve as an open-source initiative. This approach of extensively capturing the progress of an entire field, including sorting, interactive exploration and graphical representation of the data, will be applicable to many fields in materials science, engineering and biosciences.
|
|
| 4. |
- Stone, Kevin H., et al.
(författare)
-
Transformation from crystalline precursor to perovskite in PbCl2-derived MAPbI3
- 2018
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9:1
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding the formation chemistry of metal halide perovskites is key to optimizing processing conditions and realizing enhanced optoelectronic properties. Here, we reveal the structure of the crystalline precursor in the formation of methylammonium lead iodide (MAPbI3) from the single-step deposition of lead chloride and three equivalents of methylammonium iodide (PbCl2 + 3MAI) (MA = CH3NH3). The as-spun film consists of crystalline MA2PbI3Cl, which is composed of one-dimensional chains of lead halide octahedra, coexisting with disordered MACl. We show that the transformation of precursor into perovskite is not favored in the presence of MACl, and thus the gradual evaporation of MACl acts as a self-regulating mechanism to slow the conversion. We propose the stable precursor phase enables dense film coverage and the slow transformation may lead to improved crystal quality. This enhanced chemical understanding is paramount for the rational control of film deposition and the fabrication of superior optoelectronic devices.
|
|
| 5. |
- Christoforo, M. Greyson, et al.
(författare)
-
Transient response of organo-metal-halide solar cells analyzed by time-resolved current-voltage measurements
- 2015
-
Ingår i: Photonics. - : MDPI AG. - 2304-6732. ; 2:4, s. 1101-1115
-
Tidskriftsartikel (refereegranskat)abstract
- The determination of the power conversion efficiency of solar cells based on organo-metal-halides is subject to an ongoing debate. As solar cell devices may exhibit very slow transient response, current-voltage scans in different directions may not be congruent, which is an effect often referred to as hysteresis. We here discuss time-resolved current-voltage measurements as a means to evaluate appropriate delay times (voltage settling times) to be used in current-voltage measurements of solar cells. Furthermore, this method allows the analysis of transient current response to extract time constants that can be used to compare characteristic differences between devices of varying architecture types, selective contacts and changes in devices due to storage or degradation conditions.
|
|
| 6. |
- Dagar, Janardan, et al.
(författare)
-
Alkali Salts as Interface Modifiers in n-i-p Hybrid Perovskite Solar Cells
- 2019
-
Ingår i: Solar RRL. - : Wiley. - 2367-198X. ; 3:9
-
Tidskriftsartikel (refereegranskat)abstract
- After demonstration of a 23% power conversion efficiency, a high operational stability is the next most important scientific and technological challenge in perovskite solar cells (PSCs). A potential failure mechanism is tied to a bias-induced ion migration, which causes current–voltage hysteresis and a decay in the device performance over time. Herein, alkali salts are shown to mitigate hysteresis and stabilize device performance in n-i-p hybrid planar PSCs. Different alkali salts of potassium chloride, iodide, and nitrate as well as sodium chloride and iodide are deposited from aqueous solution onto the n-type contact, based on SnO2, prior to deposition of the perovskite absorber Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3. Introduction of potassium-based alkali salts suppresses the current–voltage hysteresis and stabilizes the operational device stability at the maximum power point. This is attributed to the suppression of hole trapping at the n-type selective transport layer (SnO2)/perovskite interface observed by surface photovoltage spectroscopy, which is interpreted to reduce interfacial recombination and improve charge carrier extraction. The best and most stable performance of 19% is achieved using potassium nitrate as the interface modifier. Devices with higher and more stable performance exhibit substantially lower current transients, analyzed during maximum power point tracking.
|
|
| 7. |
- Dobrovolsky, Alexander, et al.
(författare)
-
Defect-induced local variation of crystal phase transition temperature in metal-halide perovskites
- 2017
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8:1
-
Tidskriftsartikel (refereegranskat)abstract
- Solution-processed organometal halide perovskites are hybrid crystalline semiconductors highly interesting for low-cost and efficient optoelectronics. Their properties are dependent on the crystal structure. Literature shows a variety of crystal phase transition temperatures and often a spread of the transition over tens of degrees Kelvin. We explain this inconsistency by demonstrating that the temperature of the tetragonal-to-orthorhombic phase transition in methylammonium lead triiodide depends on the concentration and nature of local defects. Phase transition in individual nanowires was studied by photoluminescence microspectroscopy and super-resolution imaging. We propose that upon cooling from 160 to 140 K, domains of the crystal containing fewer defects stay in the tetragonal phase longer than highly defected domains that readily transform to the high bandgap orthorhombic phase at higher temperatures. The existence of relatively pure tetragonal domains during the phase transition leads to drastic photoluminescence enhancement, which is inhomogeneously distributed across perovskite microcrystals.
|
|
| 8. |
- Dobrovolsky, Alexander, et al.
(författare)
-
Relating Defect Luminescence and Nonradiative Charge Recombination in MAPbI3 Perovskite Films
- 2020
-
Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 11:5, s. 1714-1720
-
Tidskriftsartikel (refereegranskat)abstract
- Nonradiative losses in semiconductors are related to defects. At cryogenic temperatures, defect-related photoluminescence (PL) at energies lower than the band-edge PL is observed in methylammonium lead triiodide perovskite. We applied multispectral PL imaging to samples prepared by two different procedures and exhibiting 1 order of magnitude different PL quantum yield (PLQY). The high-PLQY sample showed concentration of the emitting defect sites around 1012-1013 cm-3. No correlation between PLQY and the relative intensity of the defect emission was found when micrometer-sized local regions of the same sample were compared. However, a clear positive correlation between the lower PLQY and higher defect emission was observed when two preparation methods were contrasted. Therefore, although the emissive defects are not connected directly with the nonradiative centers and may be spatially separated at the nano scale, chemical processes during the perovskite synthesis promote/prevent formation of both types of defects at the same time.
|
|
| 9. |
- Hermerschmidt, Felix, et al.
(författare)
-
Finally, inkjet-printed metal halide perovskite LEDs-utilizing seed crystal templating of salty PEDOT:PSS
- 2020
-
Ingår i: Materials Horizons. - : Royal Society of Chemistry (RSC). - 2051-6347 .- 2051-6355. ; 7:7, s. 1773-1781
-
Tidskriftsartikel (refereegranskat)abstract
- Solution-processable metal halide perovskites are increasingly implemented in perovskite-based light-emitting diodes (PeLEDs). Especially green PeLEDs based on methylammonium lead bromide (MAPbBr3) composites exhibit impressive optoelectronic properties, while allowing processing by low-cost and upscalable printing methods. In this study, we have investigated the influence of potassium chloride (KCl) blended into the common hole injection material poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) to boost PeLED device performance. The inclusion of KCl firstly results in a change in morphology of the PEDOT:PSS layer, which then acts as a template during deposition of the perovskite layer. A MAPbBr3:polyethylene glycol (PEG) composite was used, which does not require the deposition of an anti-solvent droplet to induce preferential perovskite crystallization and is therefore suitable for spin coating and scalable inkjet printing processes. PeLEDs utilizing the KCl induced templating effect on a planar PEDOT:PSS/MAPbBr3:PEG architecture show improved performance, predominantly due to improved crystallization. PeLEDs incorporating spin-coated perovskite layers yield a 40-fold increase in luminance (8000 cd m-2) while the turn-on voltage decreases to 2.5 V. KCl-modified PEDOT:PSS contact layers enabled the realization of inkjet-printed PeLEDs with luminance increased by a factor of 20 at a maximum of 4000 cd m-2 and a turn-on voltage of 2.5 V. This work paves the way for inkjet-printed perovskite light-emitting devices for a wide variety of low-cost and customizable applications. This journal is
|
|
| 10. |
- Johansson, Erik M. J., et al.
(författare)
-
Efficient infiltration of low molecular weight polymer in nanoporous TiO2
- 2011
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 502:4-6, s. 225-230
-
Tidskriftsartikel (refereegranskat)abstract
- The polymer APFO(3) was prepared with different molecular weights to study how the infiltration into nanoporous TiO2 films of different thickness depends on the size of the polymer. Also two different sizes of TiO2 nanoparticles were investigated to understand the effect of different pore size. It was observed that the lowest molecular weight polymer dissolved in chlorobenzene could infiltrate the nanoporous TiO2 network up to several micrometer thick films. It was concluded that efficient polymer infiltration into thick nanoporous layers was possible for the polymers with an estimated average chain length smaller than the diameter of the nanoparticles.
|
|
| 11. |
- Kegelmann, Lukas, et al.
(författare)
-
It Takes Two to Tango - Double-Layer Selective Contacts in Perovskite Solar Cells for Improved Device Performance and Reduced Hysteresis
- 2017
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 9:20, s. 17245-17255
-
Tidskriftsartikel (refereegranskat)abstract
- Solar cells made from inorganic-organic perovskites have gradually approached market requirements as their efficiency and stability have improved tremendously in recent years. Planar low-temperature processed perovskite solar cells are advantageous for possible large-scale production but are more prone to exhibiting photocurrent hysteresis, especially in the regular n-i-p structure. Here, a systematic characterization of different electron selective contacts with a variety of chemical and electrical properties in planar n-i-p devices processed below 180 °C is presented. The inorganic metal oxides TiO2 and SnO2, the organic fullerene derivatives C60, PCBM, and ICMA, as well as double-layers with a metal oxide/PCBM structure are used as electron transport materials (ETMs). Perovskite layers deposited atop the different ETMs with the herein applied fabrication method show a similar morphology according to scanning electron microscopy. Further, surface photovoltage spectroscopy measurements indicate comparable perovskite absorber qualities on all ETMs, except TiO2, which shows a more prominent influence of defect states. Transient photoluminescence studies together with current-voltage scans over a broad range of scan speeds reveal faster charge extraction, less pronounced hysteresis effects, and higher efficiencies for devices with fullerene compared to those with metal oxide ETMs. Beyond this, only double-layer ETM structures substantially diminish hysteresis effects for all performed scan speeds and strongly enhance the power conversion efficiency up to a champion stabilized value of 18.0%. The results indicate reduced recombination losses for a double-layer TiO2/PCBM contact design: First, a reduction of shunt paths through the fullerene to the ITO layer. Second, an improved hole blocking by the wide band gap metal oxide. Third, decreased transport losses due to an energetically more favorable contact, as implied by photoelectron spectroscopy measurements. The herein demonstrated improvements of multilayer selective contacts may serve as a general design guideline for perovskite solar cells.
|
|
| 12. |
- Kiligaridis, Alexander, et al.
(författare)
-
Excitation wavelength dependence of photoluminescence flickering in degraded MAPbI3 perovskite and its connection to lead iodide formation
- 2020
-
Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 222
-
Tidskriftsartikel (refereegranskat)abstract
- Metal halide perovskite semiconductors often exhibit photoluminescence blinking and flickering when luminescence of individual small nano- or even microcrystals is monitored. The nature of these fluctuations is not well understood but must be related to the presence of metastable non-radiative recombination channels and efficient charge migration in these materials. Here we report on the excitation wavelength dependence of photoluminescence flickering effect in degraded methylammonium lead iodide (MAPbI3) thin films. While the luminescence intensity is temporary stable when excited in the blue region with wavelength shorter than 530 nm, excitation with red light (wavelength longer than 530 nm) results in luminescence flickering. It is hypothesised that the wavelength dependence reflects the excitation energy dependence of the photochemical mechanism that switches non-radiative recombination channels on and off. The effect can also be related to hindered charge carrier diffusion due to their localization in the interfacial layer between MAPbI3 and PbI2 which is formed in the course of degradation.
|
|
| 13. |
- Kirchartz, Thomas, et al.
(författare)
-
Research Update : Recombination and open-circuit voltage in lead-halide perovskites
- 2018
-
Ingår i: APL Materials. - : AIP Publishing. - 2166-532X. ; 6:10
-
Tidskriftsartikel (refereegranskat)abstract
- The high open-circuit voltage and the slow recombination in lead-halide perovskite solar cells has been one of the main contributors to their success as photovoltaic materials. Here, we review the knowledge on recombination in perovskite-based solar cells, compare the situation with silicon solar cells, and introduce the parameters used to describe recombination and open-circuit voltage losses in solar cells. We first discuss the effect of lifetimes and surface recombination velocities on photovoltaic performance before we study the microscopic origin of charge-carrier lifetimes. The lifetimes depend on defect positions and densities and on the kinetic prefactors that control the phonon-assisted interaction between the extended states in the conduction and valence band and the localized defect states. We finally argue that the key to understand the long lifetimes and high open-circuit voltages is a combination of a low density of deep defects and a slow dissipation of energy via multiphonon processes due to the low phonon energies in the lead-halide perovskites.
|
|
| 14. |
- Li, Jun, et al.
(författare)
-
Luminescent Intermediates and Humidity-Dependent Room-Temperature Conversion of the MAPbI3 Perovskite Precursor
- 2018
-
Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 3:10, s. 14494-14502
-
Tidskriftsartikel (refereegranskat)abstract
- Preparation of metal-halide perovskites under room temperature attracts attention because of energy saving by removing thermal annealing. Room-temperature transformation of spin-cast wet films consisting of methylammonium (MA) iodide, PbI2, and dimethylformamide toward solid MAPbI3 perovskite proceeds via several intermediate crystalline states and is strongly dependent on ambient humidity. Light transmission and photoluminescence (PL) microscopy and spectroscopy were used to monitor the growth of crystals and transformation of their properties in time under nitrogen atmosphere at room temperature. Under low humidity, a highly luminescent intermediate phase with low absorption in the visible range appears, with the PL spectra composed of several bands in the range from 600 to 760 nm. We assign these bands to low-dimensional (nanocrystals and two-dimensional inclusions) MAPbI3 intermediates, where the exciton confinement shifts the spectrum to higher energies in comparison with the bulk MAPbI3. The intermediate levels of ambient humidity (10-50%) appear to catalyze the conversion of the intermediate phase to MAPbI3. At a high ambient humidity (>80%), the initially formed MAPbI3 is quickly transformed to the transparent hydrate phase of MAPbI3. The role of ambient water catalyzing the material transformation by competing for Pb coordination with the solvent molecules is discussed.
|
|
| 15. |
- Mathies, Florian, et al.
(författare)
-
Advances in Inkjet-Printed Metal Halide Perovskite Photovoltaic and Optoelectronic Devices
- 2020
-
Ingår i: Energy Technology. - : Wiley. - 2194-4296 .- 2194-4288. ; 8:4
-
Forskningsöversikt (refereegranskat)abstract
- Inkjet printing (IJP) has evolved over the past 30 years into a reliable, versatile, and cost-effective industrial production technology in many areas from graphics to printed electronic applications. Intensive research efforts have led to the successful development of functional electronic inks to realize printed circuit boards, sensors, lighting, actuators, energy storage, and power generation devices. Recently, a promising solution-processable material class has entered the stage: metal halide perovskites (MHPs). Within just 10 years of research, the efficiency of perovskite solar cells (PSCs) on a laboratory scale increased to over 25%. Despite the complex nature of MHPs, significant progress has also been made in controlling film formation in terms of ink development, substrate wetting behavior, and crystallization processes of inkjet-printed MHPs. This results in highly efficient inkjet-printed PSCs with a power conversion efficiency (PCE) of almost 21%, paving the way for cost-effective and highly efficient thin-film solar cell technology. In addition, the excellent optoelectronic properties of inkjet-printed MHPs achieve remarkable results in photodetectors, X-ray detectors, and illumination applications. Herein, a comprehensive overview of the state-of-the-art and recent advances in the production of inkjet-printed MHPs for highly efficient and innovative optoelectronic devices is provided.
|
|
| 16. |
- Mathies, Florian, et al.
(författare)
-
Gas flow-assisted vacuum drying : Identification of a novel process for attaining high-quality perovskite films
- 2021
-
Ingår i: Materials Advances. - : Royal Society of Chemistry (RSC). - 2633-5409. ; 2:16, s. 5365-5370
-
Tidskriftsartikel (refereegranskat)abstract
- Controlling the nucleation and crystal growth in solution-processed metal halide perovskite (MHP) thin films is the pivotal point in fabricating homogenous and pinhole-free films. Using scalable coating and printing techniques, vacuum and gas flow-assisted drying processes turn out to be the most promising methods to induce nucleation and crystallization. Yet, the exact interplay and nature of these processes are unclear. In our work, we optically monitor these processes in situ. For the first time, we can show that a controlled venting of the vacuum chamber and the use of a subsequent gas flow are key to achieve homogenous nucleation. Utilizing this gas flow-assisted vacuum drying process, we find that regular, optically dense and pinhole-free MHP layers can be fabricated via inkjet printing, which yield solar cells with a power conversion efficiency of 16%, as compared to 4.5% for vacuum drying.
|
|
| 17. |
- Merdasa, Aboma, et al.
(författare)
-
Impact of Excess Lead Iodide on the Recombination Kinetics in Metal Halide Perovskites
- 2019
-
Ingår i: ACS Energy Letters. - : American Chemical Society (ACS). - 2380-8195. ; , s. 1370-1378
-
Tidskriftsartikel (refereegranskat)abstract
- Fundmental comprehension of light-induced processes in perovskites are still scarce. One active debate surrounds the influence of excess lead iodide (PbI2) on device performance, as well as optoelectronic properties, where both beneficial and detrimental traits have been reported. Here, we study its impact on charge carrier recombination kinetics by simultaneously acquiring the photoluminescence quantum yield and time-resolved photoluminescence as a function of excitation wavelength (450-780 nm). The presence of PbI2 in the perovskite film is identified via a unique spectroscopic signature in the PLQY spectrum. Probing the recombination in the presence and absence of this signature, we detect a radiative bimolecular recombination mechanism induced by PbI2. Spatially resolving the photoluminescence, we determine that this radiative process occurs in a small volume at the PbI2/perovskite interface, which is only active when charge carriers are generated in PbI2, and therefore provide deeper insight into how excess PbI2 may improve the properties of perovskite-based devices.
|
|
| 18. |
- Merdasa, Aboma, et al.
(författare)
-
Microscopic insight into the reversibility of photodegradation in MAPbI3 thin films
- 2020
-
Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 219
-
Tidskriftsartikel (refereegranskat)abstract
- Whether optoelectronic devices based on metal-halide perovskite semiconductors will become a commercially viable technology will be determined by their intrinsic and operational stability. Recent results indicate there is some reversibility of perovskite degradation in thin films and devices, although mechanistic insight into the processes driving degradation and recovery are still scarce. We here present a comparative spectroscopic study of methylammonium lead iodide (MAPbI3) films having undergone either photo- or thermal degradation under controlled conditions. We confirm that the degradation mechanism pertaining to each type of stress is inherently different. Our results from photoluminescence microscopy measurements paint a spatially, spectrally and temporarily resolved picture showing that, unlike thermally degraded samples, photodegraded samples are in a state that intermittently recovers to luminescent MAPbI3 upon laser excitation. This indicates that rather than irreversibly decomposing, photoinduced degradation leaves MAPbI3 structurally or compositionally intact but induces defects causing non-radiative recombination losses.
|
|
| 19. |
- Merdasa, Aboma, et al.
(författare)
-
"Supertrap" at Work: Extremely Efficient Nonradiative Recombination Channels in MAPbI3 Perovskites Revealed by Luminescence Super-Resolution Imaging and Spectroscopy
- 2017
-
Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 11:6, s. 5391-5404
-
Tidskriftsartikel (refereegranskat)abstract
- Organo-metal halide perovskites are some of the most promising materials for the new generation of low-cost photovoltaic and light-emitting devices. Their solution processability is a beneficial trait, although it leads to a spatial inhomogeneity of perovskite films with a variation of the trap state density at the nanoscale. Comprehending their properties using traditional spectroscopy therefore becomes difficult, calling for a combination with microscopy in order to see beyond the ensemble-averaged response. We studied photoluminescence (PL) blinking of micrometer-sized individual methylammonium lead iodide (MAPbI3) perovskite polycrystals, as well as monocrystalline microrods up to 10 μm long. We correlated their PL dynamics with structure employing scanning electron and optical super-resolution microscopy. Combining super-resolution localization imaging and super-resolution optical fluctuation imaging (SOFI), we could detect and quantify preferential emitting regions in polycrystals exhibiting different types of blinking. We propose that blinking in MAPbI3 occurs by the activation/passivation of a "supertrap" which presumably is a donor-acceptor pair able to trap both electrons and holes. As such, nonradiative recombination via supertraps, in spite being present at a rather low concentrations (1012-1015 cm-3), is much more efficient than via all other defect states present in the material at higher concentrations (1016-1018 cm-3). We speculate that activation/deactivation of a supertrap occurs by its temporary dissociation into free donor and acceptor impurities. We found that supertraps are most efficient in structurally homogeneous and large MAPbI3 crystals where carrier diffusion is efficient, which may therefore pose limitations on the efficiency of perovskite-based devices.
|
|
| 20. |
- Oksenberg, Eitan, et al.
(författare)
-
Deconvoluting Energy Transport Mechanisms in Metal Halide Perovskites Using CsPbBr3 Nanowires as a Model System
- 2021
-
Ingår i: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 31:22
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding energy transport in metal halide perovskites is essential to effectively guide further optimization of materials and device designs. However, difficulties to disentangle charge carrier diffusion, photon recycling, and photon transport have led to contradicting reports and uncertainty regarding which mechanism dominates. In this study, monocrystalline CsPbBr3 nanowires serve as 1D model systems to help unravel the respective contribution of energy transport processes in metal-halide perovskites. Spatially, temporally, and spectrally resolved photoluminescence (PL) microscopy reveals characteristic signatures of each transport mechanism from which a robust model describing the PL signal accounting for carrier diffusion, photon propagation, and photon recycling is developed. For the investigated CsPbBr3 nanowires, an ambipolar carrier mobility of μ = 35 cm2 V−1 s−1 is determined, and is found that charge carrier diffusion dominates the energy transport process over photon recycling. Moreover, the general applicability of the developed model is demonstrated on different perovskite compounds by applying it to data provided in previous related reports, from which clarity is gained as to why conflicting reports exist. These findings, therefore, serve as a useful tool to assist future studies aimed at characterizing energy transport mechanisms in semiconductor nanowires using PL.
|
|
| 21. |
- Oksenberg, Eitan, et al.
(författare)
-
Large lattice distortions and size-dependent bandgap modulation in epitaxial halide perovskite nanowires
- 2020
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 11
-
Tidskriftsartikel (refereegranskat)abstract
- Metal-halide perovskites have been shown to be remarkable and promising optoelectronic materials. However, despite ongoing research from multiple perspectives, some fundamental questions regarding their optoelectronic properties remain controversial. One reason is the high-variance of data collected from, often unstable, polycrystalline thin films. Here we use ordered arrays of stable, single-crystal cesium lead bromide (CsPbBr3) nanowires grown by surface-guided chemical vapor deposition to study fundamental properties of these semiconductors in a one-dimensional model system. Specifically, we uncover the origin of an unusually large size-dependent luminescence emission spectral blue-shift. Using multiple spatially resolved spectroscopy techniques, we establish that bandgap modulation causes the emission shift, and by correlation with state-of-the-art electron microscopy methods, we reveal its origin in substantial and uniform lattice rotations due to heteroepitaxial strain and lattice relaxation. Understanding strain and its effect on the optoelectronic properties of these dynamic materials, from the atomic scale up, is essential to evaluate their performance limits and fundamentals of charge carrier dynamics.
|
|
| 22. |
- Phung, Nga, et al.
(författare)
-
Photoprotection in metal halide perovskites by ionic defect formation
- 2022
-
Ingår i: Joule. - : Elsevier BV. - 2542-4351. ; 6:9, s. 2152-2174
-
Tidskriftsartikel (refereegranskat)abstract
- Photostability is critical for long-term solar cell operation. While light-triggered defects are usually reported as evidence of material degradation, we reveal that the formation of certain defects in metal halide perovskites is crucial for protection against intense or prolonged light exposure. We identify an inherent self-regulating cycle of formation and recovery of ionic defects under light exposure that mitigates the overheating of the lattice due to hot carrier cooling, which allows exposure to several thousand suns without degrading. The excess energy instead dissipates by forming defects, which in turn alters the optoelectronic properties of the absorber, resulting in a temporary reduction of photon absorption. Defects gradually recover to restore the original optoelectronic properties of the absorber. Photoprotection is a key feature for the photostability in plants. Thus, finding a protection mechanism in metal halide perovskites similar to those in nature is encouraging for the development of long-term sustainable solar cells.
|
|
| 23. |
- Rehermann, Carolin, et al.
(författare)
-
Origin of Ionic Inhomogeneity in MAPb(IxBr1-x)3Perovskite Thin Films Revealed by In-Situ Spectroscopy during Spin Coating and Annealing
- 2020
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 12:27, s. 30343-30352
-
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.
|
|
| 24. |
- Schröder, Vincent R.F., et al.
(författare)
-
Bicolour, large area, inkjet-printed metal halide perovskite light emitting diodes
-
Ingår i: Materials Horizons. - 2051-6347.
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a bicoloured metal halide perovskite (MHP) light emitting diode (LED) fabricated in two sequential inkjet printing steps. By adjusting the printing parameters, we selectively and deliberately redissolve and recrystallize the first printed emissive layer to add a pattern emitting in a different color. The red light emitting features (on a green light emitting background) have a minimum size of 100 μm and originate from iodide-rich domains in a phase-segregated, mixed MHP. This phase forms between the first layer, a bromide-based MHP, which is partially dissolved by printing, and the second layer, an iodide-containing MHP. With an optimised printing process we can retain the active layer integrity and fabricate bicolour, large area MHP-based LEDs with up to 1600 mm2 active area. The two emission peaks at 535 nm and 710 nm are well separated and produce a strong visual contrast.
|
|
| 25. |
- Schröder, Vincent R.F., et al.
(författare)
-
Using Combinatorial Inkjet Printing for Synthesis and Deposition of Metal Halide Perovskites in Wavelength-Selective Photodetectors
- 2022
-
Ingår i: Advanced Engineering Materials. - : Wiley. - 1438-1656 .- 1527-2648. ; 24:4
-
Tidskriftsartikel (refereegranskat)abstract
- Metal halide perovskites have received great attention in recent years, predominantly due to the high performance of perovskite solar cells. The versatility of the material, which allows the tunability of the bandgap, has led to its use in light-emitting diodes, photo, and X-ray detectors, among other optoelectronic device applications. Specifically in photodetectors, the tunability of the bandgap allows fabrication of spectrally selective devices. Utilizing a combinatorial inkjet printing approach, multiple perovskite compositions absorbing at specific wavelengths in a single printing step are fabricated. The drop-on-demand capabilities of inkjet printing enable the deposition of inks in a precise ratio to produce specific perovskite compositions in the printed thin film. By controlling the halide ratio in the compositions, a mixed halide gradient ranging from pure MAPbI3 via MAPbBr3 to MAPbCl3 is produced. The tunability in the absorption onset from 410 to 790 nm is demonstrated, covering the whole visible spectrum, with a precision of 8 nm steps for MAPb(BrxCl1−x)3 compositions. From this range of mixed halide perovskites, photodetectors which show spectral selectivity corresponding to the measured absorption onset are demonstrated, paving the way for use in a printed visible light spectrometer without the need for a dispersion element.
|
|
