| 1. |
- Luo, Xiyu, et al.
(author)
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Effects of local compositional heterogeneity in mixed halide perovskites on blue electroluminescence
- 2024
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In: Matter. - 2590-2393. ; 7:3, s. 1054-1070
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Journal article (peer-reviewed)abstract
- Compositional heterogeneity is commonly observed in mixed bromide/iodide perovskite photoabsorbers, typically with minimal effects on charge carrier recombination and photovoltaic performance. Consistently, it has so far received very limited attention in bromide/chloride-mixed perovskites, which hold particular significance for blue light-emitting diodes. Here, we uncover that even a minor degree of localized halide heterogeneity leads to severe non-radiative losses in mixed bromide/chloride blue perovskite emitters, presenting a stark contrast to general observations in photovoltaics. We not only provide a visualization of the heterogeneity landscape spanning from micro-to sub-microscale but also identify that this issue mainly arises from the initially formed chloride-rich clusters during perovskite nucleation. Our work sheds light on a long-term neglected factor impeding the advancement of blue light-emitting diodes using mixed halide perovskites and provides a practical strategy to mitigate this issue.
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| 2. |
- Földváry Ličina, Veronika, et al.
(author)
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Development of the ASHRAE Global Thermal Comfort Database II
- 2018
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In: Building and Environment. - : Elsevier BV. - 0360-1323. ; 142, s. 502-512
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Journal article (peer-reviewed)abstract
- Recognizing the value of open-source research databases in advancing the art and science of HVAC, in 2014 the ASHRAE Global Thermal Comfort Database II project was launched under the leadership of University of California at Berkeley's Center for the Built Environment and The University of Sydney's Indoor Environmental Quality (IEQ) Laboratory. The exercise began with a systematic collection and harmonization of raw data from the last two decades of thermal comfort field studies around the world. The ASHRAE Global Thermal Comfort Database II (Comfort Database), now an online, open-source database, includes approximately 81,846 complete sets of objective indoor climatic observations with accompanying “right-here-right-now” subjective evaluations by the building occupants who were exposed to them. The database is intended to support diverse inquiries about thermal comfort in field settings. A simple web-based interface to the database enables filtering on multiple criteria, including building typology, occupancy type, subjects' demographic variables, subjective thermal comfort states, indoor thermal environmental criteria, calculated comfort indices, environmental control criteria and outdoor meteorological information. Furthermore, a web-based interactive thermal comfort visualization tool has been developed that allows end-users to quickly and interactively explore the data.
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| 3. |
- Anttu, Nicklas, et al.
(author)
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Beyond ray optics absorption of light in CsPbBr3perovskite nanowire arrays studied experimentally and with wave optics modelling
- 2023
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In: Nanotechnology. - 0957-4484. ; 35:9
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Journal article (peer-reviewed)abstract
- We study experimentally and with wave optics modelling the absorption of light in CsPbBr3perovskite nanowire arrays fabricated into periodic pores of an anodized aluminum oxide matrix, for nanowire diameters from 30 to 360 nm. First, we find that all the light that couples into the array can be absorbed by the nanowires at sufficient nanowire length. This behavior is in strong contrast to the expectation from a ray-optics description of light where, for normally incident light, only the rays that hit the cross-section of the nanowires can be absorbed. In that case, the absorption in the sample would be limited to the area fill factor of nanowires in the hexagonal array, which ranges from 13% to 58% for the samples that we study. Second, we find that the absorption saturates already at a nanowire length of 1000-2000 nm, making these perovskite nanowires promising for absorption-based applications such as solar cells and photodetectors. The absorption shows a strong diameter dependence, but for all diameters the transmission is less than 24% already at a nanowire length of 500 nm. For some diameters, the absorption exceeds that of a calculated thin film with 100% coverage. Our analysis indicates that the strong absorption in these nanowires originates from light-trapping induced by the out-of-plane disorder due to random axial position of each nanowire within its pore in the matrix.
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| 4. |
- Dierks, Hanna, et al.
(author)
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3D X-ray microscopy with a CsPbBr3 nanowire scintillator
- 2023
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In: Nano Research. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 16:1, s. 1084-1089
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Journal article (peer-reviewed)abstract
- X-ray microscopy is an essential imaging method in many scientific fields, which can be extended to three-dimensional (3D) using tomography. Recently, metal halide perovskite (MHP) nanomaterials have become a promising candidate for X-ray scintillators, due to their high light yield, high spatial resolution, and easy fabrication. Tomography requires many projections and therefore scintillators with excellent stability. This is challenging for MHPs, which often suffer from fast degradation under X-ray irradiation and ambient conditions. Here, we demonstrate that MHP scintillators of CsPbBr3 nanowires (diameter: 60 nm, length: 5–9 µm) grown in anodized aluminum oxide (CsPbBr3 NW/AAO) have sufficient stability for X-ray micro-tomography. A tomogram was taken with a Cu X-ray source over 41 h (dose 4.2 Gyair). During this period the scintillator brightness fluctuated less than 5%, which enabled a successful reconstruction. A long-term study with 2 weeks of continuous X-ray exposure (37.5 Gyair) showed less than 14% fluctuations in brightness and no long-term degradation, despite variations in the ambient relative humidity from 7.4 %RH to 34.2 %RH. The resolution was stable at (180 ± 20) 1pmm−1, i.e., about 2.8 micron. This demonstrates that CsPbBr3 NW/AAO scintillators are promising candidates for high resolution X-ray imaging detectors.
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| 5. |
- Hammarberg, Susanna, et al.
(author)
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Nanoscale X-ray Imaging of Composition and Ferroelastic Domains in Heterostructured Perovskite Nanowires : Implications for Optoelectronic Devices
- 2023
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In: ACS Applied Nano Materials. - 2574-0970. ; 6:19, s. 17698-17705
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Journal article (peer-reviewed)abstract
- Metal halide perovskites (MHPs) have garnered significant interest as promising candidates for nanoscale optoelectronic applications due to their excellent optical properties. Axially heterostructured CsPbBr3-CsPb(Br(1-x)Clx)3 nanowires can be produced by localized anion exchange of pregrown CsPbBr3 nanowires. However, characterizing such heterostructures with sufficient strain and real space resolution is challenging. Here, we use nanofocused scanning X-ray diffraction (XRD) and X-ray fluorescence (XRF) with a 60 nm beam to investigate a heterostructured MHP nanowire as well as a reference CsPbBr3 nanowire. The nano-XRD approach gives spatially resolved maps of composition, lattice spacing, and lattice tilt. Both the reference and exchanged nanowire show signs of diverse types of ferroelastic domains, as revealed by the tilt maps. The chlorinated segment shows an average Cl composition of x = 66 and x = 70% as measured by XRD and XRF, respectively. The XRD measurements give a much more consistent result than the XRF ones. These findings are consistent with photoluminescence measurements, showing x = 73%. The nominally unexchanged segment also has a small concentration of Cl, as observed with all three methods, which we attribute to diffusion after processing. These results highlight the need to prevent such unwanted processes in order to fabricate optoelectronic devices based on MHP heterostructures.
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| 6. |
- Lamers, Nils, et al.
(author)
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Gas-Phase Anion Exchange for Multisegment Heterostructured CsPb(Br1−xClx)3 Perovskite Nanowires
- 2023
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In: Advanced Optical Materials. - 2195-1071.
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Journal article (peer-reviewed)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. |
- Lamers, Nils, et al.
(author)
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Perovskite-Compatible Electron-Beam-Lithography Process Based on Nonpolar Solvents for Single-Nanowire Devices
- 2022
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In: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 5:3, s. 3177-3182
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Journal article (peer-reviewed)abstract
- Metal halide perovskites (MHPs) have been studied intensely as the active material for optoelectronic devices. Lithography methods for perovskites remain limited because of the solubility of perovskites in polar solvents. Here, we demonstrate an electron-beam-lithography process with a poly(methyl methacrylate) resist based on the nonpolar solvents o-xylene, hexane, and toluene. Features down to 50 nm size are created, and photoluminescence of CsPbBr3 nanowires exhibits no degradation. We fabricate metal contacts to single CsPbBr3 nanowires, which show a strong photoresponsivity of 0.29 A W-1. The presented method is an excellent tool for nanoscale MHP science and technology, allowing for the fabrication of complex nanostructures.
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| 8. |
- Li, Zhaojun, 1989, et al.
(author)
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9.0% power conversion efficiency from ternary all-polymer solar cells
- 2017
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In: Energy and Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 10:10, s. 2212-2221
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Journal article (peer-reviewed)abstract
- Integration of a third component into a single-junction polymer solar cell (PSC) is regarded as an attractive strategy to enhance the performance of PSCs. Although binary all-polymer solar cells (all-PSCs) have recently emerged with compelling power conversion efficiencies (PCEs), the PCEs of ternary all-PSCs still lag behind those of the state-of-the-art binary all-PSCs, and the advantages of ternary systems are not fully exploited. In this work, we realize high-performance ternary all-PSCs with record-breaking PCEs of 9% and high fill factors (FF) of over 0.7 for both conventional and inverted devices. The improved photovoltaic performance benefits from the synergistic effects of extended absorption, more efficient charge generation, optimal polymer orientations and suppressed recombination losses compared to the binary all-PSCs, as evidenced by a set of experimental techniques. The results provide new insights for developing high-performance ternary all-PSCs by choosing appropriate donor and acceptor polymers to overcome limitations in absorption, by affording good miscibility, and by benefiting from charge and energy transfer mechanisms for efficient charge generation.
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| 9. |
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| 10. |
- Li, Zhaojun, 1989, et al.
(author)
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High-Performance and Stable All-Polymer Solar Cells Using Donor and Acceptor Polymers with Complementary Absorption
- 2017
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In: Advanced Energy Materials. - : Wiley. - 1614-6832 .- 1614-6840. ; 7:14
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Journal article (peer-reviewed)abstract
- To explore the advantages of emerging all-polymer solar cells (all-PSCs), growing efforts have been devoted to developing matched donor and acceptor polymers to outperform fullerene-based PSCs. In this work, a detailed characterization and comparison of all-PSCs using a set of donor and acceptor polymers with both conventional and inverted device structures is performed. A simple method to quantify the actual composition and light harvesting contributions from the individual donor and acceptor is described. Detailed study on the exciton dissociation and charge recombination is carried out by a set of measurements to understand the photocurrent loss. It is unraveled that fine-tuned crystallinity of the acceptor, matched donor and acceptor with complementary absorption and desired energy levels, and device architecture engineering can synergistically boost the performance of all-PSCs. As expected, the PBDTTS-FTAZ:PNDI-T10 all-PSC attains a high and stable power conversion efficiency of 6.9% without obvious efficiency decay in 60 d. This work demonstrates that PNDI-T10 can be a potential alternative acceptor polymer to the widely used acceptor N2200 for high-performance and stable all-PSCs.
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