| 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. - : CELL PRESS. - 2590-2393 .- 2590-2385. ; 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. |
- Tan, Yeshu, et al.
(author)
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Highly Luminescent and Stable Perovskite Nanocrystals with Octylphosphonic Acid as a Ligand for Efficient Light-Emitting Diodes
- 2018
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In: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 10:4, s. 3784-3792
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Journal article (peer-reviewed)abstract
- All inorganic perovskite nanocrystals (NCs) of CsPbX3 (X = Cl, Br, I, or their mixture) are regarded as promising candidates for high-performance light-emitting diode (LED) owing to their high photoluminescence (PL) quantum yield (QY) and easy synthetic process. However, CsPbX3 NCs synthesized by the existing methods, where oleic acid (OA) and oleylamine (OLA) are generally used as surface-chelating ligands, suffer from poor stability due to the ligand loss, which drastically deteriorates their PL QY, as well as dispersibility in solvents. Herein, the OA/OLA ligands are replaced with octylphosphonic acid (OPA), which dramatically enhances the CsPbX3 stability. Owing to a strong interaction between OPA and lead atoms, the OPA-capped CsPbX3 (OPA-CsPbX3) NCs not only preserve their high PL QY (amp;gt;90%) but also achieve a high-quality dispersion in solvents after multiple purification processes. Moreover, the organic residue in purified OPA-CsPbBr3 is only similar to 4.6%, which is much lower than similar to 29.7% in OA/OLA-CsPbBr3. Thereby, a uniform and compact OPA-CsPbBr3 film is obtained for LED application. A green LED with a current efficiency of 18.13 cd A(-1), corresponding to an external quantum efficiency of 6.5%, is obtained. Our research provides a path to prepare high-quality perovskite NCs for high-performance optoelectronic devices.
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| 3. |
- Teng, Pengpeng, et al.
(author)
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Degradation and self-repairing in perovskite light-emitting diodes
- 2021
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In: Matter. - : Elsevier. - 2590-2393 .- 2590-2385. ; 4:11, s. 3710-3724
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Journal article (peer-reviewed)abstract
- One of the most critical challenges in perovskite light-emitting diodes (PeLEDs) lies in poor operational stability. Although field dependent ion migration is believed to play an important role in the operation of perovskite optoelectronic devices, a complete understanding of how it affects the stability of PeLEDs is still missing. Here, we report a unique self-repairing behavior that the electroluminescence of moderately degraded PeLEDs can almost completely restore to their initial performance after resting. We find that the accumulated halides within the hole transport layer undergo back diffusion toward the surface of the perovskite layer during resting, repairing the vacancies and thus resulting in electroluminescence recovery. These findings indicate that one of the dominant degradation pathways in PeLEDs is the generation of halide vacancies at perovskite/hole transport layer interface during operation. We thus further passivate this key interface, which results in a high external quantum efficiency of 22.8% and obviously improved operational stability.
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| 4. |
- Wu, Tian, et al.
(author)
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High-Performance Perovskite Light-Emitting Diode with Enhanced Operational Stability Using Lithium Halide Passivation
- 2020
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In: Angewandte Chemie International Edition. - : WILEY-V C H VERLAG GMBH. - 1433-7851 .- 1521-3773. ; 59:10, s. 4099-4105
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Journal article (peer-reviewed)abstract
- Defect passivation has been demonstrated to be effective in improving the radiative recombination of charge carriers in perovskites, and consequently, the device performance of the resultant perovskite light-emitting diodes (LEDs). State-of-the-art useful passivation agents in perovskite LEDs are mostly organic chelating molecules that, however, simultaneously sacrifice the charge-transport properties and thermal stability of the resultant perovskite emissive layers, thereby deteriorating performance, and especially the operational stability of the devices. We demonstrate that lithium halides can efficiently passivate the defects generated by halide vacancies and reduce trap state density, thereby suppressing ion migration in perovskite films. Efficient green perovskite LEDs based on all-inorganic CsPbBr3 perovskite with a peak external quantum efficiency of 16.2 %, as well as a high maximum brightness of 50 270 cd m(-2), are achieved. Moreover, the device shows decent stability even under a brightness of 10(4) cd m(-2). We highlight the universal applicability of defect passivation using lithium halides, which enabled us to improve the efficiency of blue and red perovskite LEDs.
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| 5. |
- Zou, Yatao, et al.
(author)
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Boosting Perovskite Light-Emitting Diode Performance via Tailoring Interfacial Contact
- 2018
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In: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 10:28, s. 24320-24326
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Journal article (peer-reviewed)abstract
- Solution-processed perovskite light-emitting diodes (LEDs) have attracted wide attention in the past several years. However, the overall efficiency and stability of perovskite-based LEDs remain inferior to those of organic or quantum dot LEDs. Nonradiative charge recombination and the unbalanced charge injection are two critical factors that limit the device efficiency and operational stability of perovskite LEDs. Here, we develop a strategy to modify the interface between the hole transport layer and the perovskite emissive layer with an amphiphilic conjugated polymer of poly[(9,9-bis(3-(N,N-dimethylamino)propy1)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN). We show evidences that PFN improves the quality of the perovskite film, which effectively suppresses nonradiative recombination. By further improving the charge injection balance rate, a green perovskite LED with a champion current efficiency of 45.2 cd/A, corresponding to an external quantum efficiency of 14.4%, is achieved. In addition, the device based on the PFN layer exhibits improved operational lifetime. Our work paves a facile way for the development of efficient and stable perovskite LEDs.
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| 6. |
- Zou, Yatao, et al.
(author)
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Manipulating crystallization dynamics through chelating molecules for bright perovskite emitters
- 2021
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
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Journal article (peer-reviewed)abstract
- Molecular additives are widely utilized to minimize non-radiative recombination in metal halide perovskite emitters due to their passivation effects from chemical bonds with ionic defects. However, a general and puzzling observation that can hardly be rationalized by passivation alone is that most of the molecular additives enabling high-efficiency perovskite light-emitting diodes (PeLEDs) are chelating (multidentate) molecules, while their respective monodentate counterparts receive limited attention. Here, we reveal the largely ignored yet critical role of the chelate effect on governing crystallization dynamics of perovskite emitters and mitigating trap-mediated non-radiative losses. Specifically, we discover that the chelate effect enhances lead-additive coordination affinity, enabling the formation of thermodynamically stable intermediate phases and inhibiting halide coordination-driven perovskite nucleation. The retarded perovskite nucleation and crystal growth are key to high crystal quality and thus efficient electroluminescence. Our work elucidates the full effects of molecular additives on PeLEDs by uncovering the chelate effect as an important feature within perovskite crystallization. As such, we open new prospects for the rationalized screening of highly effective molecular additives.
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| 7. |
- Zou, Yatao, et al.
(author)
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Protocol for efficient and self-healing near-infrared perovskite light-emitting diodes.
- 2022
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In: STAR protocols. - : Cell Press. - 2666-1667. ; 3:3
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Journal article (peer-reviewed)abstract
- Preparation of highly efficient and stable perovskite light-emitting diodes (PeLEDs) with reproducible device performance is challenging. This protocol describes steps for fabrication of high-performance and self-healing PeLEDs. These include instructions for synthesis of charge-transporting zinc oxide (ZnO) nanocrystals, step-by-step device fabrication, and control over self-healing of the degraded devices. For complete details on the use and execution of this protocol, please refer to Teng et al. (2021).
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| 8. |
- Zou, Yatao, et al.
(author)
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Spectral-Stable Blue Emission from Moisture-Treated Low-Dimensional Lead Bromide-Based Perovskite Films
- 2019
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In: ACS Photonics. - : AMER CHEMICAL SOC. - 2330-4022. ; 6:7, s. 1728-1735
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Journal article (peer-reviewed)abstract
- Highly efficient light-emitting diodes (LEDs) based on metal halide perovskites with green, red, and near-infrared electro-luminescence have been widely demonstrated. However, the development of their blue counterparts is still hampered due to the difficult deposition of efficient and spectral-stable blue-emitting active layers. Here, we report a facile and general approach that uses a moisture treatment in combination with the precursor stoichiometry engineering for the fabrication of efficient and color stable blue-emitting perovskite films. We find that, with a short-term moisture exposure, light emission from Ruddlesden Popper lead bromide-based perovskite films exhibit a continuous blue-shift from 512 to 475 nm through incorporating excess CsBr in the precursors. In addition, we observe that the formed Cs4PbBr6 phase under CsBr-rich condition is favorable to stabilize the blue emission of the resulting films. The corresponding blue-emitting perovskite films exhibit a photoluminescence quantum efficiency of over 20%, delivering sky-blue perovskite LEDs with no change in the light emission even under high voltage. Our strategy provides an alternative way for realizing efficient and spectrally stable active layers for the further development of blue-emitting perovskite LEDs.
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| 9. |
- Zou, Yatao, et al.
(author)
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Thermal-induced interface degradation in perovskite light-emitting diodes
- 2020
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In: Journal of Materials Chemistry C. - : ROYAL SOC CHEMISTRY. - 2050-7526 .- 2050-7534. ; 8:43, s. 15079-15085
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Journal article (peer-reviewed)abstract
- Perovskite light-emitting diodes (PeLEDs) have experienced rapid improvements in device efficiency during the last several years. However, the operational instability of PeLEDs remains a key barrier hindering their practical applications. A fundamental understanding of the degradation mechanism is still lacking but will be important to seek ways to mitigate these unwanted processes. In this work, through comprehensive characterizations of the perovskite emitters and the interfacial contacts, we figure out that Joule heating induced interface degradation is one of the dominant factors affecting the operational stability of PeLEDs. We investigate the interfacial contacts of PeLEDs based on a commonly used device structure, with an organic electron transport layer of 1,3,5-tris(N-phenylbenzimiazole-2-yl)benzene (TPBi), and observe obvious photoluminescence quenching of the perovskite layer after device operation. Detailed characterizations of the interlayers and the interfacial contacts reveal that photoluminescence quenching is mainly due to the element inter-diffusion at the interface induced by the morphological evolution of the TPBi layers under Joule heating during the operation of PeLEDs. Our work provides direct insights into the degradation pathways and highlights the importance of exploring intrinsically stable interlayers as well as interfacial contacts beyond the state-of-the-art to further boost the operational stability of PeLEDs.
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