| 1. |
- Gil-Escrig, Lidon, et al.
(author)
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Efficient Wide-Bandgap Mixed-Cation and Mixed-Halide Perovskite Solar Cells by Vacuum Deposition
- 2021
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In: ACS Energy Letters. - : American Chemical Society (ACS). - 2380-8195. ; 6:2, s. 827-836
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Journal article (peer-reviewed)abstract
- Vacuum deposition methods are increasingly applied to the preparation of perovskite films and devices, in view of the possibility to prepare multilayer structures at low temperature. Vacuum-deposited, wide-bandgap solar cells based on mixed-cation and mixed-anion perovskites have been scarcely reported, due to the challenges associated with the multiple-source processing of perovskite thin films. In this work, we describe a four-source vacuum deposition process to prepare wide-bandgap perovskites of the type FA(1-n)Cs(n)Pb-(I1-xBrx)(3) with a tunable bandgap and controlled morphology, using FAI, CsI, PbI2, and PbBr2 as the precursors. The simultaneous sublimation of PbI2 and PbBr2 allows the relative Br/Cs content to be decoupled and controlled, resulting in homogeneous perovskite films with a bandgap in the 1.7-1.8 eV range and no detectable halide segregation. Solar cells based on 1.75 eV bandgap perovskites show efficiency up to 16.8% and promising stability, maintaining 90% of the initial efficiency after 2 weeks of operation.
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| 2. |
- Kaihovirta, Nikolai, et al.
(author)
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Self-absorption in a light-emitting electrochemical cell based on an ionic transition metal complex
- 2015
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 106:10
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Journal article (peer-reviewed)abstract
- We report on the quantitative and qualitative effects of self-absorption in light-emitting electrochemical cells (LECs) based on ionic transition metal complexes (iTMCs), as measured in-situ during electric driving. A yellow-emitting iTMC-LEC comprising an active material thickness of 95 nm suffers a 4% loss of the emission intensity to self-absorption, whereas the same type of device but with a larger active-material thickness of 1 mu m will lose a significant 40% of the light intensity. We also find that the LEC-specific effect of doping-induced self-absorption can result in a drift of the emission spectrum with time for iTMC-LECs, but note that the overall magnitude of doping-induced self-absorption is much smaller than for conjugated-polymer LECs.
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| 3. |
- Meier, Sebastian B., et al.
(author)
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Dynamic Doping in Planar Ionic Transition Metal Complex-Based Light-Emitting Electrochemical Cells
- 2013
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In: Advanced Functional Materials. - : Wiley-VCH Verlag. - 1616-301X .- 1616-3028. ; 23:28, s. 3531-3538
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Journal article (peer-reviewed)abstract
- Using a planar electrode geometry, the operational mechanism of iridium(III) ionic transition metal complex (iTMC)-based light-emitting electrochemical cells (LECs) is studied by a combination of fluorescence microscopy and scanning Kelvin probe microscopy (SKPM). Applying a bias to the LECs leads to the quenching of the photoluminescence (PL) in between the electrodes and to a sharp drop of the electrostatic potential in the middle of the device, far away from the contacts. The results shed light on the operational mechanism of iTMC-LECs and demonstrate that these devices work essentially the same as LECs based on conjugated polymers do, i.e., according to an electrochemical doping mechanism. Moreover, with proceeding operation time the potential drop shifts towards the cathode coincident with the onset of light emission. During prolonged operation the emission zone and the potential drop both migrate towards the anode. This event is accompanied by a continuous quenching of the PL in two distinct regions separated by the emission line.
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| 4. |
- Susic, Isidora, et al.
(author)
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Intrinsic Organic Semiconductors as Hole Transport Layers in p–i–n Perovskite Solar Cells
- 2022
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In: Solar RRL. - : John Wiley & Sons. - 2367-198X. ; 6:4
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Journal article (peer-reviewed)abstract
- Thin polymeric and small-molecular-weight organic semiconductors are widely employed as hole transport layers (HTLs) in perovskite solar cells. To ensure ohmic contact with the electrodes, the use of doping or additional high work function (WF) interlayer is common. In some cases, however, intrinsic organic semiconductors can be used without any additive or buffer layers, although their thickness must be tuned to ensure selective and ohmic hole transport. Herein, the characteristics of thin HTLs in vacuum-deposited perovskite solar cells are studied, and it is found that only very thin (<5 nm) HTLs readily result inhigh-performing devices, as the HTL acts as a WF enhancer while still ensuring selective hole transfer, as suggested by ultraviolet photoemission spectroscopy and Kelvin probe measurements. For thicker films (>= 5 nm), a dynamic behavior for consecutive electrical measurements is observed, a phenomenon which is also common to other widely used HTLs. Finally, it is found that despite their glass transition temperature, small-molecule HTLs lead to thermally unstable solar cells, asopposed to polymeric materials. The origin of the degradation is still not clear, but might be related to chemical reactions/diffusion at the HTL/perovskite interface, in detriment of the device stability
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| 5. |
- van Reenen, Stephan, et al.
(author)
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Universal Transients in Polymer and Ionic Transition Metal Complex Light-Emitting Electrochemical Cells
- 2013
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In: Journal of the American Chemical Society. - : American Chemical Society. - 0002-7863 .- 1520-5126. ; 135:2, s. 886-891
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Journal article (peer-reviewed)abstract
- Two types of light-emitting electrochemical cells (LECs) are commonly distinguished, the polymer-based LEC (p-LEC) and the ionic transition metal complex-based LEC (iTMC-LEC). Apart from marked differences in the active layer constituents, these LEC types typically show operational time scales that can differ by many orders of magnitude at room temperature. Here, we demonstrate that despite these differences p-LECs and iTMC-LECs show current, light output, and efficacy transients that follow a universal shape. Moreover, we conclude that the turn-on time of both LEC types is dominated by the ion conductivity because the turn-on time exhibits the same activation energy as the ion conductivity in the off-state. These results demonstrate that both types of LECs are really two extremes of one class of electroluminescent devices. They also implicate that no fundamental difference exists between charge transport in small molecular weight or polymeric mixed ionic and electronic conductive materials. Additionally, it follows that the ionic conductivity is responsible for the dynamic properties of devices and systems using them. This likely extends to mixed ionic and electronic conductive materials used in organic solar cells and in a variety of biological systems.
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| 6. |
- Vasilopoulou, Maria, et al.
(author)
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Advances in solution-processed near-infrared light-emitting diodes
- 2021
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In: Nature Photonics. - : NATURE PORTFOLIO. - 1749-4885 .- 1749-4893. ; 15:9, s. 656-669
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Research review (peer-reviewed)abstract
- A summary of recent advances in the near-infrared light-emitting diodes that are fabricated by solution-processed means, with coverage of devices based on organic semiconductors, halide perovskites and colloidal quantum dots. Near-infrared light-emitting diodes based on solution-processed semiconductors, such as organics, halide perovskites and colloidal quantum dots, have emerged as a viable technological platform for biomedical applications, night vision, surveillance and optical communications. The recently gained increased understanding of the relationship between materials structure and photophysical properties has enabled the design of efficient emitters leading to devices with external quantum efficiencies exceeding 20%. Despite considerable strides made, challenges remain in achieving high radiance, reducing efficiency roll-off and extending operating lifetime. This Review summarizes recent advances on emissive materials synthetic methods and device key attributes that collectively contribute to improved performance of the fabricated light-emitting devices.
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