“Edge stabilization in reduced-dimensional perovskites”. Quan LN, Ma D, Zhao Y, Voznyy O, Yuan H, Bladt E, Pan J, de Arquer FPG, Sabatini R, Piontkowski Z, Emwas A-H, Todorovic P, Quintero-Bermudez R, Walters G, Fan JZ, Liu M, Tan H, Saidaminov M I, Gao L, Li Y, Anjum DH, Wei N, Tang J, McCamant DW, Roeffaers MBJ, Bals S, Hofkens J, Bakr OM, Lu Z-H, Sargent EH, Nature Communications 11, 170 (2020). http://doi.org/10.1038/S41467-019-13944-2
Abstract: Reduced-dimensional perovskites are attractive light-emitting materials due to their efficient luminescence, color purity, tunable bandgap, and structural diversity. A major limitation in perovskite light-emitting diodes is their limited operational stability. Here we demonstrate that rapid photodegradation arises from edge-initiated photooxidation, wherein oxidative attack is powered by photogenerated and electrically-injected carriers that diffuse to the nanoplatelet edges and produce superoxide. We report an edge-stabilization strategy wherein phosphine oxides passivate unsaturated lead sites during perovskite crystallization. With this approach, we synthesize reduced-dimensional perovskites that exhibit 97 +/- 3% photoluminescence quantum yields and stabilities that exceed 300 h upon continuous illumination in an air ambient. We achieve green-emitting devices with a peak external quantum efficiency (EQE) of 14% at 1000 cd m(-2); their maximum luminance is 4.5 x 10(4) cd m(-2) (corresponding to an EQE of 5%); and, at 4000 cd m(-2), they achieve an operational half-lifetime of 3.5 h.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 16.6
Times cited: 147
DOI: 10.1038/S41467-019-13944-2
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“Imaging heterogeneously distributed photo-active traps in perovskite single crystals”. Yuan H, Debroye E, Bladt E, Lu G, Keshavarz M, Janssen KPF, Roeffaers MBJ, Bals S, Sargent EH, Hofkens J, Advanced materials 30, 1705494 (2018). http://doi.org/10.1002/ADMA.201705494
Abstract: Organic-inorganic halide perovskites (OIHPs) have demonstrated outstanding energy conversion efficiency in solar cells and light-emitting devices. In spite of intensive developments in both materials and devices, electronic traps and defects that significantly affect their device properties remain under-investigated. Particularly, it remains challenging to identify and to resolve traps individually at the nanoscopic scale. Here, photo-active traps (PATs) are mapped over OIHP nanocrystal morphology of different crystallinity by means of correlative optical differential super-resolution localization microscopy (Delta-SRLM) and electron microscopy. Stochastic and monolithic photoluminescence intermittency due to individual PATs is observed on monocrystalline and polycrystalline OIHP nanocrystals. Delta-SRLM reveals a heterogeneous PAT distribution across nanocrystals and determines the PAT density to be 1.3 x 10(14) and 8 x 10(13) cm(-3) for polycrystalline and for monocrystalline nanocrystals, respectively. The higher PAT density in polycrystalline nanocrystals is likely related to an increased defect density. Moreover, monocrystalline nanocrystals that are prepared in an oxygen and moisture-free environment show a similar PAT density as that prepared at ambient conditions, excluding oxygen or moisture as chief causes of PATs. Hence, it is conduded that the PATs come from inherent structural defects in the material, which suggests that the PAT density can be reduced by improving crystalline quality of the material.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 19.791
Times cited: 29
DOI: 10.1002/ADMA.201705494
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“Spontaneous self-assembly of Perovskite nanocrystals into electronically coupled supercrystals : toward filling the green gap”. Tong Y, Yao E-P, Manzi A, Bladt E, Wang K, Doeblinger M, Bals S, Mueller-Buschbaum P, Urban AS, Polavarapu L, Feldmann J, Advanced materials 30, 1801117 (2018). http://doi.org/10.1002/ADMA.201801117
Abstract: Self-assembly of nanoscale building blocks into ordered nanoarchitectures has emerged as a simple and powerful approach for tailoring the nanoscale properties and the opportunities of using these properties for the development of novel optoelectronic nanodevices. Here, the one-pot synthesis of CsPbBr3 perovskite supercrystals (SCs) in a colloidal dispersion by ultrasonication is reported. The growth of the SCs occurs through the spontaneous self-assembly of individual nanocrystals (NCs), which form in highly concentrated solutions of precursor powders. The SCs retain the high photoluminescence (PL) efficiency of their NC subunits, however also exhibit a redshifted emission wavelength compared to that of the individual nanocubes due to interparticle electronic coupling. This redshift makes the SCs pure green emitters with PL maxima at approximate to 530-535 nm, while the individual nanocubes emit a cyan-green color (approximate to 512 nm). The SCs can be used as an emissive layer in the fabrication of pure green light-emitting devices on rigid or flexible substrates. Moreover, the PL emission color is tunable across the visible range by employing a well-established halide ion exchange reaction on the obtained CsPbBr3 SCs. These results highlight the promise of perovskite SCs for light emitting applications, while providing insight into their collective optical properties.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 19.791
Times cited: 161
DOI: 10.1002/ADMA.201801117
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“A Facet-Specific Quantum Dot Passivation Strategy for Colloid Management and Efficient Infrared Photovoltaics”. Kim Y, Che F, Jo JW, Choi J, de Arquer FPG, Voznyy O, Sun B, Kim J, Choi M-J, Quintero-Bermudez R, Fan F, Tan CS, Bladt E, Walters G, Proppe AH, Zou C, Yuan H, Bals S, Hofkens J, Roeffaers MBJ, Hoogland S, Sargent EH, Advanced materials 31, 1805580 (2019). http://doi.org/10.1002/ADMA.201805580
Abstract: Colloidal nanocrystals combine size- and facet-dependent properties with solution processing. They offer thus a compelling suite of materials for technological applications. Their size- and facet-tunable features are studied in synthesis; however, to exploit their features in optoelectronic devices, it will be essential to translate control over size and facets from the colloid all the way to the film. Larger-diameter colloidal quantum dots (CQDs) offer the attractive possibility of harvesting infrared (IR) solar energy beyond absorption of silicon photovoltaics. These CQDs exhibit facets (nonpolar (100)) undisplayed in small-diameter CQDs; and the materials chemistry of smaller nanocrystals fails consequently to translate to materials for the short-wavelength IR regime. A new colloidal management strategy targeting the passivation of both (100) and (111) facets is demonstrated using distinct choices of cations and anions. The approach leads to narrow-bandgap CQDs with impressive colloidal stability and photoluminescence quantum yield. Photophysical studies confirm a reduction both in Stokes shift (approximate to 47 meV) and Urbach tail (approximate to 29 meV). This approach provides a approximate to 50% increase in the power conversion efficiency of IR photovoltaics compared to controls, and a approximate to 70% external quantum efficiency at their excitonic peak.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 19.791
Times cited: 74
DOI: 10.1002/ADMA.201805580
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“Dopant-induced electron localization drives CO2 reduction to C2 hydrocarbons”. Zhou Y, Che F, Liu M, Zou C, Liang Z, De Luna P, Yuan H, Li J, Wang Z, Xie H, Li H, Chen P, Bladt E, Quintero-Bermudez R, Sham T-K, Bals S, Hofkens J, Sinton D, Chen G, Sargent EH, Nature chemistry 10, 974 (2018). http://doi.org/10.1038/S41557-018-0092-X
Abstract: The electrochemical reduction of CO2 to multi-carbon products has attracted much attention because it provides an avenue to the synthesis of value-added carbon-based fuels and feedstocks using renewable electricity. Unfortunately, the efficiency of CO2 conversion to C-2 products remains below that necessary for its implementation at scale. Modifying the local electronic structure of copper with positive valence sites has been predicted to boost conversion to C-2 products. Here, we use boron to tune the ratio of Cu delta+ to Cu-0 active sites and improve both stability and C-2-product generation. Simulations show that the ability to tune the average oxidation state of copper enables control over CO adsorption and dimerization, and makes it possible to implement a preference for the electrosynthesis of C-2 products. We report experimentally a C-2 Faradaic efficiency of 79 +/- 2% on boron-doped copper catalysts and further show that boron doping leads to catalysts that are stable for in excess of similar to 40 hours while electrochemically reducing CO2 to multi-carbon hydrocarbons.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 25.87
Times cited: 700
DOI: 10.1038/S41557-018-0092-X
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