Colloidal quantum dots (CQDs) allow broad tuning of the bandgap across the visible and near-infrared spectral regions. Recent advances in applying CQDs in light sensing, photovoltaics, and light ...emission have heightened interest in achieving further synthetic improvements. In particular, improving monodispersity remains a key priority in order to improve solar cells’ open-circuit voltage, decrease lasing thresholds, and improve photodetectors’ noise-equivalent power. Here we utilize machine-learning-in-the-loop to learn from available experimental data, propose experimental parameters to try, and, ultimately, point to regions of synthetic parameter space that will enable record-monodispersity PbS quantum dots. The resultant studies reveal that adding a growth-slowing precursor (oleylamine) allows nucleation to prevail over growth, a strategy that enables record-large-bandgap (611 nm exciton) PbS nanoparticles with a well-defined excitonic absorption peak (half-width at half-maximum (hwhm) of 145 meV). At longer wavelengths, we also achieve improved monodispersity, with an hwhm of 55 meV at 950 nm and 24 meV at 1500 nm, compared to the best published to date values of 75 and 26 meV, respectively.
Metal halide perovskites show promise for light-emitting diodes (LEDs) owing to their facile manufacture and excellent optoelectronic performance, including high color purity and spectral stability, ...especially in the green region. However, for blue perovskite LEDs, the emission spectrum line width is broadened to over 25 nm by the coexistence of multiple reduced-dimensional perovskite domains, and the spectral stability is poor, with an undesirable shift (over 7 nm) toward longer wavelengths under operating conditions, degradation that occurs due to phase separation when mixed halides are employed. Here we demonstrate chloride insertion-immobilization, a strategy that enables blue perovskite LEDs, the first to exhibit narrowband (line width of 18 nm) and spectrally stable (no wavelength shift) performance. We prepare bromide-based perovskites and then employ organic chlorides for dynamic treatment, inserting and in situ immobilizing chlorides to blue-shift and stabilize the emission. We achieve sky-blue LEDs with a record luminance over 5100 cd/m2 at 489 nm, and an operating half-life of 51 min at 1500 cd/m2. By device structure optimization, we further realize an improved EQE of 5.2% at 479 nm and an operating half-life of 90 min at 100 cd/m2.
The electrochemical carbon dioxide reduction reaction (CO2RR) produces diverse chemical species. Cu clusters with a judiciously controlled surface coordination number (CN) provide active sites that ...simultaneously optimize selectivity, activity, and efficiency for CO2RR. Here we report a strategy involving metal–organic framework (MOF)-regulated Cu cluster formation that shifts CO2 electroreduction toward multiple-carbon product generation. Specifically, we promoted undercoordinated sites during the formation of Cu clusters by controlling the structure of the Cu dimer, the precursor for Cu clusters. We distorted the symmetric paddle-wheel Cu dimer secondary building block of HKUST-1 to an asymmetric motif by separating adjacent benzene tricarboxylate moieties using thermal treatment. By varying materials processing conditions, we modulated the asymmetric local atomic structure, oxidation state and bonding strain of Cu dimers. Using electron paramagnetic resonance (EPR) and in situ X-ray absorption spectroscopy (XAS) experiments, we observed the formation of Cu clusters with low CN from distorted Cu dimers in HKUST-1 during CO2 electroreduction. These exhibited 45% C2H4 faradaic efficiency (FE), a record for MOF-derived Cu cluster catalysts. A structure–activity relationship was established wherein the tuning of the Cu–Cu CN in Cu clusters determines the CO2RR selectivity.
Efficient wide-bandgap perovskite solar cells (PSCs) enable high-efficiency tandem photovoltaics when combined with crystalline silicon and other low-bandgap absorbers. However, wide-bandgap PSCs ...today exhibit performance far inferior to that of sub-1.6-eV bandgap PSCs due to their tendency to form a high density of deep traps. Here, we show that healing the deep traps in wide-bandgap perovskites-in effect, increasing the defect tolerance via cation engineering-enables further performance improvements in PSCs. We achieve a stabilized power conversion efficiency of 20.7% for 1.65-eV bandgap PSCs by incorporating dipolar cations, with a high open-circuit voltage of 1.22 V and a fill factor exceeding 80%. We also obtain a stabilized efficiency of 19.1% for 1.74-eV bandgap PSCs with a high open-circuit voltage of 1.25 V. From density functional theory calculations, we find that the presence and reorientation of the dipolar cation in mixed cation-halide perovskites heals the defects that introduce deep trap states.
In tandem catalysis, two distinct catalytic materials are interfaced to feed the product of one reaction into the next one. This approach, analogous to enzyme cascades, can potentially be used to ...upgrade small molecules such as CO2 to more valuable hydrocarbons. Here, we investigate the materials chemistry of metal–organic framework (MOF) thin films grown on gold nanostructured microelectrodes (AuNMEs), focusing on the key materials chemistry challenges necessary to enable the applications of these MOF/AuNME composites in tandem catalysis. We applied two growth methodslayer-by-layer and solvothermalto grow a variety of MOF thin films on AuNMEs and then characterized them using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The MOF@AuNME materials were then evaluated for electrocatalytic CO2 reduction. The morphology and crystallinity of the MOF thin films were examined, and it was found that MOF thin films were capable of dramatically suppressing CO production on AuNMEs and producing further-reduced carbon products such as CH4 and C2H4. This work illustrates the use of MOF thin films to tune the activity of an underlying CO2RR catalyst to produce further-reduced products.
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
; their maximum luminance is 4.5 × 10
cd m
(corresponding to an EQE of 5%); and, at 4000 cd m
, they achieve an operational half-lifetime of 3.5 h.
Mixed Lead Halide Passivation of Quantum Dots Fan, James Z.; Andersen, Nigel T.; Biondi, Margherita ...
Advanced materials (Weinheim),
11/2019, Letnik:
31, Številka:
48
Journal Article
Recenzirano
Infrared‐absorbing colloidal quantum dots (IR CQDs) are materials of interest in tandem solar cells to augment perovskite and cSi photovoltaics (PV). Today's best IR CQD solar cells rely on the use ...of passivation strategies based on lead iodide; however, these fail to passivate the entire surface of IR CQDs. Lead chloride passivated CQDs show improved passivation, but worse charge transport. Lead bromide passivated CQDs have higher charge mobilities, but worse passivation. Here a mixed lead‐halide (MPbX) ligand exchange is introduced that enables thorough surface passivation without compromising transport. MPbX–PbS CQDs exhibit properties that exceed the best features of single lead‐halide PbS CQDs: they show improved passivation (43 ± 5 meV vs 44 ± 4 meV in Stokes shift) together with higher charge transport (4 × 10‐2 ± 3 × 10‐3 cm2 V‐1 s‐1 vs 3 × 10‐2 ± 3 × 10‐3 cm2 V‐1 s‐1 in mobility). This translates into PV devices having a record IR open‐circuit voltage (IR Voc) of 0.46 ± 0.01 V while simultaneously having an external quantum efficiency of 81 ± 1%. They provide a 1.7× improvement in the power conversion efficiency of IR photons (>1.1 µm) relative to the single lead‐halide controls reported herein.
Infrared colloidal quantum dot (IR CQD) solar cells harvest solar power beyond the band edge of crystalline silicon. Using single lead halides for ligand exchange improves IR CQD passivation or transport, but not both. A mixed halide ligand exchange method improves both metrics, resulting in IR solar cells with improved power conversion efficiencies.
Abstract
The electroreduction of C
1
feedgas to high-energy-density fuels provides an attractive avenue to the storage of renewable electricity. Much progress has been made to improve selectivity to ...C
1
and C
2
products, however, the selectivity to desirable high-energy-density C
3
products remains relatively low. We reason that C
3
electrosynthesis relies on a higher-order reaction pathway that requires the formation of multiple carbon-carbon (C-C) bonds, and thus pursue a strategy explicitly designed to couple C
2
with C
1
intermediates. We develop an approach wherein neighboring copper atoms having distinct electronic structures interact with two adsorbates to catalyze an asymmetric reaction. We achieve a record
n
-propanol Faradaic efficiency (FE) of (33 ± 1)% with a conversion rate of (4.5 ± 0.1) mA cm
−2
, and a record
n
-propanol cathodic energy conversion efficiency (EE
cathodic half-cell
) of 21%. The FE and EE
cathodic half-cell
represent a 1.3× improvement relative to previously-published CO-to-
n
-propanol electroreduction reports.
Colloidal quantum dots (CQDs) are of interest in light of their solution‐processing and bandgap tuning. Advances in the performance of CQD optoelectronic devices require fine control over the ...properties of each layer in the device materials stack. This is particularly challenging in the present best CQD solar cells, since these employ a p‐type hole‐transport layer (HTL) implemented using 1,2‐ethanedithiol (EDT) ligand exchange on top of the CQD active layer. It is established that the high reactivity of EDT causes a severe chemical modification to the active layer that deteriorates charge extraction. By combining elemental mapping with the spatial charge collection efficiency in CQD solar cells, the key materials interface dominating the subpar performance of prior CQD PV devices is demonstrated. This motivates to develop a chemically orthogonal HTL that consists of malonic‐acid‐crosslinked CQDs. The new crosslinking strategy preserves the surface chemistry of the active layer beneath, and at the same time provides the needed efficient charge extraction. The new HTL enables a 1.4× increase in charge carrier diffusion length in the active layer; and as a result leads to an improvement in power conversion efficiency to 13.0% compared to EDT standard cells (12.2%).
A chemically orthogonal hole transport layer for lead sulfide colloidal quantum dot (CQD) solar cells is introduced. By substituting the 1,2‐ethanedithiol‐treated CQDs with malonic‐acid‐treated CQDs, the surface chemistry of the active layer is preserved. This increases the charge diffusion length by 1.4×, enabling near‐unity charge extraction efficiency at the back electrode, achieving 13.0% efficiency.
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