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1.
J Phys Chem Lett ; : 3691-3697, 2021 Apr 08.
Artigo em Inglês | MEDLINE | ID: mdl-33829780

RESUMO

The strong excitonic effect in monolayer transition-metal dichalcogenides (TMDs) endows them with intriguing optoelectronic properties but also short-lived population and valley polarization. Exciton dissociation by interfacial charge transfer has been shown as an effective approach to prolonging excited-state lifetimes. Herein, by ultrafast spectroscopy and building-block molecule C60, we investigated exciton and valley polarization dynamics in the prototypical WSe2/C60 inorganic-organic hybrid. We show that excitons in WSe2 can be dissociated through ultrafast (∼1 ps) electron transfer to C60, with nanosecond charge separation due to thermally activated electron diffusion in C60 film. Because of suppressed electron-hole exchange interaction after electron transfer, hole in WSe2 exhibits a spin/valley polarization lifetime of ∼60 ps at room temperature, more than 2 orders of magnitude longer than that in WSe2 monolayer. This study suggests exciton dissociation as a general approach to suppress electron-hole interaction and prolong the charge/spin/valley lifetime in TMDs.

2.
J Am Chem Soc ; 2021 Apr 30.
Artigo em Inglês | MEDLINE | ID: mdl-33929193

RESUMO

Axially, epitaxially organizing nano-objects of distinct compositions and structures into superlattice nanowires enables full utilization of sunlight, readily engineered band structures, and tunable geometric parameters to fit carrier transport, thus holding great promise for optoelectronics and solar-to-fuel conversion. To maximize their efficiency, the general and high-precision synthesis of colloidal axial superlattice nanowires (ASLNWs) with programmable compositions and structures is the prerequisite; however, it remains challenging. Here, we report an axial encoding methodology toward the ASLNW library with precise control over their compositions, dimensions, crystal phases, interfaces, and periodicity. Using a predesigned, editable nanoparticle framework that offers the synthetic selectivity, we are able to chemically decouple adjacent sub-objects in ASLNWs and thus craft them in a controlled approach, yielding a library of distinct ASLNWs. We integrate therein plasmonic, metallic, or near-infrared-active chalcogenides, which hold great potential in solar energy conversion. Such synthetic capability enables a performance boost in target applications, as we report order-of-magnitude enhanced photocatalytic hydrogen production rates using optimized ASLNWs compared to corresponding solo objects. Furthermore, it is expected that such unique superlattice nanowires could bring out new phenomena.

3.
Artigo em Inglês | MEDLINE | ID: mdl-33797187

RESUMO

Despite the remarkable progress achieved in recent years, organic photovoltaics (OPVs) still need work to approach the delicate balance between efficiency, stability, and cost. Herein, two fully non-fused electron acceptors, PTB4F and PTB4Cl, are developed via a two-step synthesis from single aromatic units. The introduction of a two-dimensional chain and halogenated terminals for these non-fused acceptors plays a synergistic role in optimizing their solid stacking and orientation, thus promoting an elongated exciton lifetime and fast charge-transfer rate in bulk heterojunction blends. As a result, PTB4Cl, upon blending with PBDB-TF polymer, has enabled single-junction OPVs with power conversion efficiencies of 12.76 %, representing the highest values among the reported fully unfused electron acceptors so far.

4.
ACS Nano ; 2021 Mar 09.
Artigo em Inglês | MEDLINE | ID: mdl-33689306

RESUMO

Controlling the optical response of two-dimensional (2D) layered materials is critical for their optoelectronic and photonic applications. Current transient optical modulation of 2D semiconductors is mainly based on the band filling effect, which requires internal exciton/charge occupation from photoexcitation or charge injection. However, 2D atomically thin layers exhibit a strong excitonic effect and environmental sensitivity, offering exciting opportunities to engineer their optical properties through an external dielectric or electronic environment. Here, using femtosecond transient absorption spectroscopy as a tool and transition-metal dichalcogenide (TMD) van der Waals heterostructures with type I band alignment, we show the transient absorption modulation of the TMD layer by excitons at ultimate proximity without direct photoexcitation or exciton/charge occupation. Further layer-dependent study indicates the presence of excitons reduces the exciton oscillator strength in adjacent layers through the electric field effect because of environmental sensitivity and proximity of 2D materials. This result demonstrates the transient optical modulation with decoupled light absorption and modulation components and suggests an alternative approach to control the optical response of 2D materials for optoelectronic and photonic applications.

5.
Adv Mater ; : e2007177, 2021 Mar 19.
Artigo em Inglês | MEDLINE | ID: mdl-33742493

RESUMO

The intrinsic electronic properties of donor (D) and acceptor (A) materials in coupling with morphological features dictate the output in organic solar cells (OSCs). New physical properties of intimate eutectic mixing are used in nonfullerene-acceptor-based D-A1 -A2 ternary blends to fine-tune the bulk heterojunction thin film morphology as well as their electronic properties. With enhanced thin film crystallinity and improved carrier transport, a significant JSC amplification is achieved due to the formation of eutectic fibrillar lamellae and reduced defects state density. Material wise, aligned cascading energy levels with much larger driving force, and suppressed recombination channels confirm efficient charge transfer and transport, enabling an improved power conversion efficiency (PCE) of 17.84%. These results reveal the importance of utilizing specific material interactions to control the crystalline habit in blended films to form a well-suited morphology in guiding superior performances, which is of high demand in the next episode of OSC fabrication toward 20% PCE.

6.
J Phys Chem Lett ; : 151-156, 2020 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-33320004

RESUMO

Although the power conversion efficiencies (PCEs) of the state-of-the-art organic solar cells (OSCs) have exceeded 17%, the organic photovoltaic devices still suffer from considerable voltage losses compared with the inorganic or perovskite solar cells. Therefore, the optimization of open-circuit voltage (VOC) is of great significance for the improvement of the photovoltaic performance of OSCs. The origins of VOC have been well-established in the binary system; however, the understanding of VOC in non-fullerene acceptor (NFA)-based ternary OSCs is still lacking. Herein, we have developed a series of ternary organic photovoltaic devices, exhibiting nearly linear increased VOC as the increase of ITIC third content. We found that both the effective charge-transfer (CT) states and the nonradiative recombination losses of the bulk-heterojunction (BHJ) are altered in the ternary blends, and they collectively contribute to the tunable VOC. Our results provide a perspective for understanding the origin of VOC in NFA-based ternary OSCs.

7.
Nat Commun ; 11(1): 6368, 2020 Dec 11.
Artigo em Inglês | MEDLINE | ID: mdl-33311483

RESUMO

Among light-based free-space communication platforms, mid-infrared (MIR) light pertains to important applications in biomedical engineering, environmental monitoring, and remote sensing systems. Integrating MIR generation and reception in a network using two identical devices is vital for the miniaturization and simplification of MIR communications. However, conventional MIR emitters and receivers are not bidirectional due to intrinsic limitations of low performance and often require cryogenic cooling. Here, we demonstrate that macroscopic graphene fibres (GFs) assembled from weakly-coupled graphene layers allow room-temperature MIR detection and emission with megahertz modulation frequencies due to the persistence of photo-thermoelectric effect in millimeter-length and the ability to rapidly modulate gray-body radiation. Based on the dual-functionality of GFs, we set up a system that conducts bidirectional data transmission by switching modes between two identical GFs. The room-temperature operation of our systems and the potential to produce GFs on industrial textile-scale offer opportunities for simplified and wearable optical communications.

8.
Sci Adv ; 6(47)2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-33219022

RESUMO

Two-dimensional lead halide perovskites with confined excitons have shown exciting potentials in optoelectronic applications. It is intriguing but unclear how the soft and polar lattice redefines excitons in layered perovskites. Here, we reveal the intrinsic exciton properties by investigating exciton spin dynamics, which provides a sensitive probe to exciton coulomb interactions. Compared to transition metal dichalcogenides with comparable exciton binding energy, we observe orders of magnitude smaller exciton-exciton interaction and, counterintuitively, longer exciton spin lifetime at higher temperature. The anomalous spin dynamics implies that excitons exist as exciton polarons with substantially weakened inter- and intra-excitonic interactions by dynamic polaronic screening. The combination of strong light matter interaction from reduced dielectric screening and weakened inter-/intra-exciton interaction from dynamic polaronic screening explains their exceptional performance and provides new rules for quantum-confined optoelectronic and spintronic systems.

9.
Adv Mater ; : e2006178, 2020 Nov 16.
Artigo em Inglês | MEDLINE | ID: mdl-33191531

RESUMO

Quantum-dot light-emitting diodes (QLEDs) promise a new generation of high-performance, large-area, and cost-effective electroluminescent devices for both display and solid-state lighting technologies. However, a positive ageing process is generally required to improve device performance for state-of-the-art QLEDs. Here, it is revealed that the in situ reactions induced by organic acids in the commonly used encapsulation acrylic resin lead to positive ageing and, most importantly, the progression of in situ reactions inevitably results in negative ageing, i.e., deterioration of device performance after long-term shelf storage. In-depth mechanism studies focusing on the correlations between the in situ chemical reactions and the shelf-ageing behaviors of QLEDs inspire the design of an electron-transporting bilayer, which delivers both improved electrical conductivity and suppressed interfacial exciton quenching. This material innovation enables red QLEDs exhibiting neglectable changes of external quantum efficiency (>20.0%) and ultralong operational lifetime (T95 : 5500 h at 1000 nits) after storage for 180 days. This work provides design principles for oxide electron-transporting layers to realize shelf-stable and high-operational-performance QLEDs, representing a new starting point for both fundamental studies and practical applications.

10.
Nano Lett ; 20(11): 8212-8219, 2020 Nov 11.
Artigo em Inglês | MEDLINE | ID: mdl-33044075

RESUMO

Multiple exciton generation (MEG) in semiconductors that yields two or more excitons by absorbing one high-energy photon has been proposed to break the Shockley-Queisser limit and boost photon-to-electron conversion efficiency. However, MEG performance in conventional bulk semiconductors or later colloidal nanocrystals is far from satisfactory. Here, we report efficient MEG in few-layer black phosphorus (BP), a direct narrow bandgap two-dimensional (2D) semiconductor with layer-tunable properties. MEG performance improves with decreasing layer number and reaches 2.09Eg threshold and 93% efficiency for two-layer BP, approaching energy conservation limit. The enhanced MEG can be attributed to strong Coulomb interaction and high density of states in 2D materials. Furthermore, MEG of BP shows negligible degradation in vertical heterostructure and multielectron can be extracted by interfacial transfer with near unity yield. These results suggest 2D semiconductors as an ideal system for next generation highly efficient light emission and charge transfer devices.

11.
J Am Chem Soc ; 142(39): 16557-16561, 2020 Sep 30.
Artigo em Inglês | MEDLINE | ID: mdl-32916045

RESUMO

Herein we develop a new pillar[5]arene-mediated supramolecular polymerization strategy to control the assembly of dyes 4,7-di-2-thienyl-2,1,3-benzothiadiazole and 4,7-di-2-thienyl-2,1,3-benzoselenadiazole in the solid state. The resulting supramolecular polymeric structures drive the dye aggregates in the solid state from parallel alignments to highly ordered "head-to-tail" structures, which effectively suppresses excimer formation and thus aggregation-caused quenching effects and enhances the solid-state emission efficiency by almost 1 order of magnitude. This, together with two-photon excited emission, endows these solid-state polymers with exciting potential in optoelectronic, photonic, and bioimaging applications.

12.
Small ; : e2002524, 2020 Aug 18.
Artigo em Inglês | MEDLINE | ID: mdl-32812331

RESUMO

Metal nanoclusters with distinct photophysical and photochemical properties have drawn intense research interests for their applications in optoelectronics, catalysis, and biomedicine. Herein, strong evidence is provided that light metal is capable of generating comparable optical responses of noble metal nanoclusters, but at much shorter wavelength. Air-stable, size-uniform, sub-3 nm aluminum nanocrystals are prepared with simple solution based synthetic procedures, with photoluminescence located in the ultraviolet range and short exciton lifetime. Partial modulation of the photoluminescence is achieved, indicating the key role of surface oxides. This work is envisioned to inspire new frontiers of nanocluster research with light metals.

13.
J Chem Phys ; 153(4): 044705, 2020 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-32752698

RESUMO

Energy loss from hot-carrier cooling sets the thermodynamic limit for the photon-to-power conversion efficiency in optoelectronic applications. Efficient hot-electron extraction before cooling could reduce the energy loss and leads to efficient next generation devices, which, unfortunately, is challenging to achieve in conventional semiconductors. In this work, we explore hot-electron transfer in two-dimensional (2D) layered semiconductor heterostructures, which have shown great potential for exploring new physics and optoelectronic applications. Using broadband micro-area ultrafast spectroscopy, we firmly established a type I band alignment in the WS2-MoTe2 heterostructure and ultrafast (∼60 fs) hot-electron transfer from photoexcited MoTe2 to WS2. The hot-electron transfer efficiency increases with excitation energy or excess energy as a result of a more favorable continuous competition between resonant electron transfer and cooling, reaching 90% for hot electrons with 0.3 eV excess energy. This study reveals exciting opportunities of designing extremely thin absorber and hot-carrier devices using 2D semiconductors and also sheds important light on the photoinduced interfacial process including charge transfer and generation in 2D heterostructures and optoelectronic devices.

14.
Adv Mater ; 32(36): e2002784, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32697407

RESUMO

2D perovskite solar cells with high stability and high efficiency have attracted significant attention. A systematical static and dynamic structure investigation is carried out to show the details of 2D morphology evolution. A dual additive approach is used, where the synergy between an alkali metal cation and a polar solvent leads to high-quality 2D perovskite films with sandwich-type structures and vertical phase segregation. Such novel structure can induce high-quality 2D slab growth and reduce internal and surface defects, resulting in a high device efficiency of 16.48% with enhanced continuous illumination stability and improved moisture (55-60%) and thermal (85 °C) tolerances. Transient absorption spectra reveal the carrier migration from low n to high n species with different kinetics. An [PbI6 ]4- octagon coalescence transformation mechanism coupled with metal and organic cations wrapped is proposed. By solvent vapor annealing, a recrystallization and reorientation of the 2D perovskite slabs occurs to form an ideal structure with improved device performance and stability.

15.
Light Sci Appl ; 9: 112, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32637079

RESUMO

X-rays are widely used in probing inside information nondestructively, enabling broad applications in the medical radiography and electronic industries. X-ray imaging based on emerging lead halide perovskite scintillators has received extensive attention recently. However, the strong self-absorption, relatively low light yield and lead toxicity of these perovskites restrict their practical applications. Here, we report a series of nontoxic double-perovskite scintillators of Cs2Ag0.6Na0.4In1-yBiyCl6. By controlling the content of the heavy atom Bi3+, the X-ray absorption coefficient, radiative emission efficiency, light yield and light decay were manipulated to maximise the scintillator performance. A light yield of up to 39,000 ± 7000 photons/MeV for Cs2Ag0.6Na0.4In0.85Bi0.15Cl6 was obtained, which is much higher than that for the previously reported lead halide perovskite colloidal CsPbBr3 (21,000 photons/MeV). The large Stokes shift between the radioluminescence (RL) and absorption spectra benefiting from self-trapped excitons (STEs) led to a negligible self-absorption effect. Given the high light output and fast light decay of this scintillator, static X-ray imaging was attained under an extremely low dose of ∼1 µGyair, and dynamic X-ray imaging of finger bending without a ghosting effect was demonstrated under a low-dose rate of 47.2 µGyair s-1. After thermal treatment at 85 °C for 50 h followed by X-ray irradiation for 50 h in ambient air, the scintillator performance in terms of the RL intensity and X-ray image quality remained almost unchanged. Our results shed light on exploring highly competitive scintillators beyond the scope of lead halide perovskites, not only for avoiding toxicity but also for better performance.

16.
Adv Mater ; 32(32): e2001621, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32613625

RESUMO

Clean energy production and saving play vital impacts on the sustainability of the global community. Herein, high-performance semitransparent organic solar cells (ST-OSCs) with excellent features of power generation, being see-through, and infrared reflection of heat dissipation, with promising perspectives for building-integrated photovoltaics (BIPVs) are reported. To simultaneously improve average visible transmittance (AVT) and power conversion efficiency (PCE), formally in a trade-off relationship, of ST-OSCs, new ternary blends with alloy-like near-infrared (NIR) acceptors are employed, which are effective to improve device efficiency while maintaining visible absorption unchanged, resulting in PCEs of 16.8% for opaque devices and 13.1% for semitransparent OSCs (AVT of 22.4% and infrared photon radiation rejection (IRR) of 77%). Further, multifunctional ST-OSCs are realized via introducing simple, yet effective photonic reflectors, together with optical simulation, leading to not only perfect fitting of the visible transmittance peak (555 nm) to the photopic response of the human eye but also an excellent IRR of 90% (780-2500 nm), along with 23% AVT and over 12% PCE. This is thought to be the best-performing multifunctional ST-OSC with promising prospects as BIPVs in terms of power generation, heat dissipation, and being see-through.

17.
Nat Commun ; 11(1): 2944, 2020 Jun 10.
Artigo em Inglês | MEDLINE | ID: mdl-32522995

RESUMO

Non-noble metal plasmonic materials, e.g. doped semiconductor nanocrystals, compared to their noble metal counterparts, have shown unique advantages, including broadly tunable plasmon frequency (from visible to infrared) and rich surface chemistry. However, the fate and harvesting of hot electrons from these non-noble metal plasmons have been much less explored. Here we report plasmon driven hot electron generation and transfer from plasmonic metal oxide nanocrystals to surface adsorbed molecules by ultrafast transient absorption spectroscopy. We show unambiguously that under infrared light excitation, hot electron transfers in ultrafast timescale (<50 fs) with an efficiency of 1.4%. The excitation wavelength and fluence dependent study indicates that hot electron transfers right after Landau damping before electron thermalization. We revealed the efficiency-limiting factors and provided improvement strategies. This study paves the way for designing efficient infrared light absorption and photochemical conversion applications based on non-noble metal plasmonic materials.

18.
Nat Commun ; 11(1): 2897, 2020 Jun 09.
Artigo em Inglês | MEDLINE | ID: mdl-32518297

RESUMO

Deciphering the complicated excited-state process is critical for the development of luminescent materials with controllable emissions in different applications. Here we report the emergence of a photo-induced structural distortion accompanied by an electron redistribution in a series of gold nanoclusters. Such unexpected slow process of excited-state transformation results in near-infrared dual emission with extended photoluminescent lifetime. We demonstrate that this dual emission exhibits highly sensitive and ratiometric response to solvent polarity, viscosity, temperature and pressure. Thus, a versatile luminescent nano-sensor for multiple environmental parameters is developed based on this strategy. Furthermore, we fully unravel the atomic-scale structural origin of this unexpected excited-state transformation, and demonstrate control over the transition dynamics by tailoring the bi-tetrahedral core structures of gold nanoclusters. Overall, this work provides a substantial advance in the excited-state physical chemistry of luminescent nanoclusters and a general strategy for the rational design of next-generation nano-probes, sensors and switches.

19.
Adv Mater ; 32(24): e2001160, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-32390241

RESUMO

Low energy loss and efficient charge separation under small driving forces are the prerequisites for realizing high power conversion efficiency (PCE) in organic photovoltaics (OPVs). Here, a new molecular design of nonfullerene acceptors (NFAs) is proposed to address above two issues simultaneously by introducing asymmetric terminals. Two NFAs, BTP-S1 and BTP-S2, are constructed by introducing halogenated indandione (A1 ) and 3-dicyanomethylene-1-indanone (A2 ) as two different conjugated terminals on the central fused core (D), wherein they share the same backbone as well-known NFA Y6, but at different terminals. Such asymmetric NFAs with A1 -D-A2 structure exhibit superior photovoltaic properties when blended with polymer donor PM6. Energy loss analysis reveals that asymmetric molecule BTP-S2 with six chlorine atoms attached at the terminals enables the corresponding devices to give an outstanding electroluminescence quantum efficiency of 2.3 × 10-2 %, one order of magnitude higher than devices based on symmetric Y6 (4.4 × 10-3 %), thus significantly lowering the nonradiative loss and energy loss of the corresponding devices. Besides, asymmetric BTP-S1 and BTP-S2 with multiple halogen atoms at the terminals exhibit fast hole transfer to the donor PM6. As a result, OPVs based on the PM6:BTP-S2 blend realize a PCE of 16.37%, higher than that (15.79%) of PM6:Y6-based OPVs. A further optimization of the ternary blend (PM6:Y6:BTP-S2) results in a best PCE of 17.43%, which is among the highest efficiencies for single-junction OPVs. This work provides an effective approach to simultaneously lower the energy loss and promote the charge separation of OPVs by molecular design strategy.

20.
J Phys Chem A ; 124(21): 4185-4192, 2020 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-32353232

RESUMO

The singlet fission (SF) process converts one high-energy singlet exciton to two low-energy triplet excitons after absorbing one photon. Organic photovoltaic devices based on the SF process have shown great potential in solar energy conversion to exceed Shockley-Queisser limit. The key to SF photovoltaic devices requires efficient electron transfer (ET) from triplet exciton after SF, which is yet to be thoroughly investigated. Here, we performed thorough photophysical studies in 6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene)/C60 heterostructures using TIPS-pentacene microsize single crystal as a well-defined model system. We show the SF process in TIPS-pentacene single crystal occurs by a two-step process, with triplet pair intermediates forming in 75 fs and then dissociating to non-interacting triplets in 1.6 ps. The SF process in single crystal is comparable to that in polycrystalline film. Importantly, we observe a considerable fraction of singlet excitons is quenched by ultrafast (<75 fs) interfacial ET prior to fission and no ET from triplet excitons in 1.5 ns time window. We confirm that the absence of ET is not limited by exciton diffusion but due to very slow (≫1.5 ns) interfacial ET from triplet exciton. The observations contradict expected singlet and triplet ET behaviors based on a simple two-state Marcus ET model and suggest long-range interfacial ET from delocalized photoexcitation. The ultrafast ET from singlet exciton before SF and slow ET from triplet exciton call for reconsideration and careful design of efficient SF photovoltaic devices.

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