Room-Temperature Triple-Ligand Surface Engineering Synergistically Boosts Ink Stability, Recombination Dynamics, and Charge Injection toward EQE-11.6% Perovskite QLEDs
TL;DR: A room-temperature triple-ligand surface engineering strategy to play the synergistic role of short ligands of tetraoctylammonium bromide, DDAB, and octanoic acid toward "ideal" perovskite QDs results in the highly efficient QD-based LEDs (QLEDs).
Abstract: Developing low-cost and high-quality quantum dots (QDs) or nanocrystals (NCs) and their corresponding efficient light-emitting diodes (LEDs) is crucial for the next-generation ultra-high-definition flexible displays. Here, there is a report on a room-temperature triple-ligand surface engineering strategy to play the synergistic role of short ligands of tetraoctylammonium bromide (TOAB), didodecyldimethylammonium bromide (DDAB), and octanoic acid (OTAc) toward "ideal" perovskite QDs with a high photoluminescence quantum yield (PLQY) of >90%, unity radiative decay in its intrinsic channel, stable ink characteristics, and effective charge injection and transportation in QD films, resulting in the highly efficient QD-based LEDs (QLEDs). Furthermore, the QD films with less nonradiative recombination centers exhibit improved PL properties with a PLQY of 61% through dopant engineering in A-site. The robustness of such properties is demonstrated by the fabrication of green electroluminescent LEDs based on CsPbBr3 QDs with the peak external quantum efficiency (EQE) of 11.6%, and the corresponding peak internal quantum efficiency (IQE) and power efficiency are 52.2% and 44.65 lm W-1 , respectively, which are the most-efficient perovskite QLEDs with colloidal CsPbBr3 QDs as emitters up to now. These results demonstrate that the as-obtained QD inks have a wide range application in future high-definition QD displays and high-quality lightings.
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TL;DR: In this article, the authors describe visible-light-emitting perovskite LEDs that surpass the quantum efficiency milestone of 20.3 per cent, which is achieved by a new strategy for managing the compositional distribution in the device.
Abstract: Metal halide perovskite materials are an emerging class of solution-processable semiconductors with considerable potential for use in optoelectronic devices1–3. For example, light-emitting diodes (LEDs) based on these materials could see application in flat-panel displays and solid-state lighting, owing to their potential to be made at low cost via facile solution processing, and could provide tunable colours and narrow emission line widths at high photoluminescence quantum yields4–8. However, the highest reported external quantum efficiencies of green- and red-light-emitting perovskite LEDs are around 14 per cent7,9 and 12 per cent8, respectively—still well behind the performance of organic LEDs10–12 and inorganic quantum dot LEDs13. Here we describe visible-light-emitting perovskite LEDs that surpass the quantum efficiency milestone of 20 per cent. This achievement stems from a new strategy for managing the compositional distribution in the device—an approach that simultaneously provides high luminescence and balanced charge injection. Specifically, we mixed a presynthesized CsPbBr3 perovskite with a MABr additive (where MA is CH3NH3), the differing solubilities of which yield sequential crystallization into a CsPbBr3/MABr quasi-core/shell structure. The MABr shell passivates the nonradiative defects that would otherwise be present in CsPbBr3 crystals, boosting the photoluminescence quantum efficiency, while the MABr capping layer enables balanced charge injection. The resulting 20.3 per cent external quantum efficiency represents a substantial step towards the practical application of perovskite LEDs in lighting and display. A strategy for managing the compositional distribution in metal halide perovskite light-emitting diodes enables them to surpass 20% external quantum efficiency—a step towards their practical application in lighting and displays.
2,346 citations
TL;DR: This review summarizes the mechanisms of intrinsic- and extrinsic-environment-induced decomposition of perovskite quantum dots and some possible solutions to improve the stability of PQDs together with suggestions for further improving the performance of pc-LEDs as well as the device lifetime.
Abstract: Beyond the unprecedented success achieved in photovoltaics (PVs), lead halide perovskites (LHPs) have shown great potential in other optoelectronic devices. Among them, nanometer-scale perovskite quantum dots (PQDs) with fascinating optical properties including high brightness, tunable emission wavelength, high color purity, and high defect tolerance have been regarded as promising alternative down-conversion materials in phosphor-converted light-emitting diodes (pc-LEDs) for lighting and next-generation of display technology. Despite the promising applications of perovskite materials in various fields, they have received strong criticism for the lack of stability. The poor stability has also attracted much attention. Within a few years, numerous strategies towards enhancing the stability have been developed. This review summarizes the mechanisms of intrinsic- and extrinsic-environment-induced decomposition of PQDs. Simultaneously, the strategies for improving the stability of PQDs are reviewed in detail, which can be classified into four types: (1) compositional engineering; (2) surface engineering; (3) matrix encapsulation; (4) device encapsulation. Finally, the challenges for applying PQDs in pc-LEDs are highlighted, and some possible solutions to improve the stability of PQDs together with suggestions for further improving the performance of pc-LEDs as well as the device lifetime are provided.
751 citations
Ludwig Maximilian University of Munich1, University of Cambridge2, University of Hyderabad3, Katholieke Universiteit Leuven4, Massachusetts Institute of Technology5, University of Antwerp6, Indian Institute of Science7, Yantai University8, King Abdullah University of Science and Technology9, University of Vigo10, Nanjing University of Science and Technology11, University of California, Berkeley12, Lawrence Berkeley National Laboratory13, Nanyang Technological University14, Soochow University (Suzhou)15, Technische Universität München16, ETH Zurich17, Lund University18, Hokkaido University19, Chinese Academy of Sciences20, University of California, Santa Cruz21, Beijing Institute of Technology22, City University of Hong Kong23, University of Texas at Austin24, Indian Association for the Cultivation of Science25, San Diego State University26, University of Washington27, Texas A&M University28, Bilkent University29, James I University30, Max Planck Society31, National Renewable Energy Laboratory32, University of Valencia33, Shanghai Jiao Tong University34, Istituto Italiano di Tecnologia35, Swiss Federal Laboratories for Materials Science and Technology36, University of Notre Dame37, Monash University, Clayton campus38, Imperial College London39
TL;DR: A comprehensive review of metal-halide perovskite nanocrystals can be found in this article, where researchers having expertise in different fields (chemistry, physics, and device engineering) have joined together to provide a state-of-the-art overview and future prospects of metalhalide nanocrystal research.
Abstract: Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent colloidal nanocrystals, as well as their tunable and intriguing optical and electronic properties, has attracted researchers from different disciplines of science and technology. In the last few years, there has been a significant progress in the shape-controlled synthesis of perovskite nanocrystals and understanding of their properties and applications. In this comprehensive review, researchers having expertise in different fields (chemistry, physics, and device engineering) of metal-halide perovskite nanocrystals have joined together to provide a state of the art overview and future prospects of metal-halide perovskite nanocrystal research.
471 citations
TL;DR: The proposed OIHL passivation strategy positions perovskite QDs as an extremely promising prospect in future applications of high-definition displays, high-quality lightings, as well as solar cells.
Abstract: Perovskite quantum dots (QDs) with high photoluminescence quantum yields (PLQYs) and narrow emission peak hold promise for next-generation flexible and high-definition displays. However, perovskite QD films often suffer from low PLQYs due to the dynamic characteristics between the QD's surface and organic ligands and inefficient electrical transportation resulting from long hydrocarbon organic ligands as highly insulating barrier, which impair the ensuing device performance. Here, a general organic-inorganic hybrid ligand (OIHL) strategy is reported on to passivate perovskite QDs for highly efficient electroluminescent devices. Films based on QDs through OIHLs exhibit enhanced radiative recombination and effective electrical transportation properties compared to the primal QDs. After the OIHL passivation, QD-based light-emitting diodes (QLEDs) exhibit a maximum peak external quantum efficiency (EQE) of 16.48%, which is the most efficient electroluminescent device in the field of perovskite-based LEDs up to date. The proposed OIHL passivation strategy positions perovskite QDs as an extremely promising prospect in future applications of high-definition displays, high-quality lightings, as well as solar cells.
356 citations
TL;DR: Wang et al. realize smooth and pinhole-free, small-grained inorganic perovskite films with improved photoluminescence quantum yield by introducing trifluoroacetate anions to effectively passivate surface defects and control the crystal growth.
Abstract: Quantum efficiencies of organic-inorganic hybrid lead halide perovskite light-emitting devices (LEDs) have increased significantly, but poor device operational stability still impedes their further development and application. All-inorganic perovskites show better stability than the hybrid counterparts, but the performance of their respective films used in LEDs is limited by the large perovskite grain sizes, which lowers the radiative recombination probability and results in grain boundary related trap states. We realize smooth and pinhole-free, small-grained inorganic perovskite films with improved photoluminescence quantum yield by introducing trifluoroacetate anions to effectively passivate surface defects and control the crystal growth. As a result, efficient green LEDs based on inorganic perovskite films achieve a high current efficiency of 32.0 cd A−1 corresponding to an external quantum efficiency of 10.5%. More importantly, our all-inorganic perovskite LEDs demonstrate a record operational lifetime, with a half-lifetime of over 250 h at an initial luminance of 100 cd m−2. All-inorganic cesium lead bromide perovskite based light-emitting diodes show improved operational stability but the film quality limits their performance. Here Wang et al. use trifluoroacetate anions to passivate defects and achieve excellent device performance and stability.
315 citations
References
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TL;DR: The compelling combination of enhanced optical properties and chemical robustness makes CsPbX3 nanocrystals appealing for optoelectronic applications, particularly for blue and green spectral regions (410–530 nm), where typical metal chalcogenide-based quantum dots suffer from photodegradation.
Abstract: Metal halides perovskites, such as hybrid organic–inorganic CH3NH3PbI3, are newcomer optoelectronic materials that have attracted enormous attention as solution-deposited absorbing layers in solar cells with power conversion efficiencies reaching 20%. Herein we demonstrate a new avenue for halide perovskites by designing highly luminescent perovskite-based colloidal quantum dot materials. We have synthesized monodisperse colloidal nanocubes (4–15 nm edge lengths) of fully inorganic cesium lead halide perovskites (CsPbX3, X = Cl, Br, and I or mixed halide systems Cl/Br and Br/I) using inexpensive commercial precursors. Through compositional modulations and quantum size-effects, the bandgap energies and emission spectra are readily tunable over the entire visible spectral region of 410–700 nm. The photoluminescence of CsPbX3 nanocrystals is characterized by narrow emission line-widths of 12–42 nm, wide color gamut covering up to 140% of the NTSC color standard, high quantum yields of up to 90%, and radiativ...
6,170 citations
TL;DR: In this article, a review describes the rapid progress that has been made in hybrid organic-inorganic perovskite solar cells and their applications in the photovoltaic sector.
Abstract: Within the space of a few years, hybrid organic–inorganic perovskite solar cells have emerged as one of the most exciting material platforms in the photovoltaic sector. This review describes the rapid progress that has been made in this area.
5,463 citations
TL;DR: In this article, a hybrid organic/inorganic electroluminescent device was constructed based on the recombination of holes injected into a layer of semiconducting p-paraphenylene vinylene (PPV) with electrons injected into the multilayer film of cadmium selenide nanocrystals.
Abstract: ELECTROLUMINESCENT devices have been developed recently that are based on new materials such as porous silicon1 and semiconducting polymers2,3. By taking advantage of developments in the preparation and characterization of direct-gap semiconductor nanocrystals4–6, and of electroluminescent polymers7, we have now constructed a hybrid organic/inorganic electroluminescent device. Light emission arises from the recombination of holes injected into a layer of semiconducting p-paraphenylene vinylene (PPV)8–10 with electrons injected into a multilayer film of cadmium selenide nanocrystals. Close matching of the emitting layer of nanocrystals with the work function of the metal contact leads to an operating voltage11 of only 4V. At low voltages emission from the CdSe layer occurs. Because of the quantum size effect19–24 the colour of this emission can be varied from red to yellow by changing the nanocrystal size. At higher voltages green emission from the polymer layer predominates. Thus this device has a degree of voltage tunability of colour.
3,783 citations
TL;DR: It is shown, using photoluminescence studies, that radiative bimolecular recombination is dominant at higher excitation densities, Hence, the quantum efficiencies of the perovskite light-emitting diodes increase at higher current densities.
Abstract: Solid-state light-emitting devices based on direct-bandgap semiconductors have, over the past two decades, been utilized as energy-efficient sources of lighting. However, fabrication of these devices typically relies on expensive high-temperature and high-vacuum processes, rendering them uneconomical for use in large-area displays. Here, we report high-brightness light-emitting diodes based on solution-processed organometal halide perovskites. We demonstrate electroluminescence in the near-infrared, green and red by tuning the halide compositions in the perovskite. In our infrared device, a thin 15 nm layer of CH3NH3PbI(3-x)Cl(x) perovskite emitter is sandwiched between larger-bandgap titanium dioxide (TiO2) and poly(9,9'-dioctylfluorene) (F8) layers, effectively confining electrons and holes in the perovskite layer for radiative recombination. We report an infrared radiance of 13.2 W sr(-1) m(-2) at a current density of 363 mA cm(-2), with highest external and internal quantum efficiencies of 0.76% and 3.4%, respectively. In our green light-emitting device with an ITO/PEDOT:PSS/CH3NH3PbBr3/F8/Ca/Ag structure, we achieved a luminance of 364 cd m(-2) at a current density of 123 mA cm(-2), giving external and internal quantum efficiencies of 0.1% and 0.4%, respectively. We show, using photoluminescence studies, that radiative bimolecular recombination is dominant at higher excitation densities. Hence, the quantum efficiencies of the perovskite light-emitting diodes increase at higher current densities. This demonstration of effective perovskite electroluminescence offers scope for developing this unique class of materials into efficient and colour-tunable light emitters for low-cost display, lighting and optical communication applications.
3,466 citations
Journal Article•
TL;DR: In this article, a hybrid organic/inorganic electroluminescent device was constructed based on the recombination of holes injected into a layer of semiconducting p-paraphenylene vinylene (PPV) with electrons injected into the multilayer film of cadmium selenide nanocrystals.
Abstract: ELECTROLUMINESCENT devices have been developed recently that are based on new materials such as porous silicon' and semiconducting polymers 2,3 . By taking advantage of developments in the preparation and characterization of direct-gap semiconductor nanocrystals 4-6 , and of electroluminescent polymers7, we have now constructed a hybrid organic/inorganic electroluminescent device. Light emission arises from the recombination of holes injected into a layer of semiconducting p-paraphenylene vinylene (PPV) 2-10 with electrons injected into a multilayer film of cadmium selenide nanocrystals. Close matching of the emitting layer of nanocrystals with the work function of the metal contact leads to an operating voltage" of only 4 V. At low voltages emission from the CdSe layer occurs. Because of the quantum size effect 19-24 the colour of this emission can be varied from red to yellow by changing the nanocrystal size. At higher voltages green emission from the polymer layer predominates. Thus this device has a degree of voltage tunability of colour.
3,285 citations