RESUMO
The realization of low-cost photodetectors with high sensitivity, high quantum efficiency, high gain and fast photoresponse in the visible and short-wave infrared remains one of the challenges in optoelectronics. Two classes of photodetectors that have been developed are photodiodes and phototransistors, each of them with specific drawbacks. Here we merge both types into a hybrid photodetector device by integrating a colloidal quantum dot photodiode atop a graphene phototransistor. Our hybrid detector overcomes the limitations of a phototransistor in terms of speed, quantum efficiency and linear dynamic range. We report quantum efficiencies in excess of 70%, gain of 10(5) and linear dynamic range of 110 dB and 3 dB bandwidth of 1.5 kHz. This constitutes a demonstration of an optoelectronically active device integrated directly atop graphene and paves the way towards a generation of flexible highly performing hybrid two-dimensional (2D)/0D optoelectronics.
RESUMO
The preparation of homoleptic heterometallic complexes still remains a challenge. Herein, we report the synthesis and characterization of [Au(PMe3)2][{AuHg2(o-C6F4)3}{Hg3(o-C6F4)3}] (), a gold-mercury homoleptic metallacycle. The crystal structure of displays two [Hg2M(o-C6F4)3] (M = Au(I), Hg(II)) units linked through a short AuHg contact of 3.097(2) Å, the strongest unsupported Au(I)Hg(II) interaction described to date. Theoretical calculations quantify the interaction between the trimetalic units as -199 kJ mol(-1), a surprisingly strong value.
RESUMO
We present a simple conceptual model describing the absorption enhancement provided by diffraction gratings due to resonant coupling to guided modes in a multi-layered structure. In doing so, we provide insight into why certain guided modes are more strongly excited than others and demonstrate that the spatial overlap of the mode profile with the grating is important. The model is verified by comparison to optical simulations and experimental measurements. We fabricate metal nanoparticle gratings integrated as back contacts in solution-processed PbS colloidal quantum dot photodiodes. The measured photocurrent at the target wavelength is enhanced by 250%, with reference to planar devices, due to resonant coupling to guided modes with strong spatial overlap with the gratings. In comparison, resonant coupling to weakly overlapping modes results in a 25% increase at the same wavelength.
RESUMO
Metallic nanoparticles tailor the electronic properties of PbS colloidal quantum dots in a post-synthetic, all solution-processable approach. The Fermi level of the resulting nanocomposites can be tuned from p- to n-type due to remote charge transfer and electron trap state passivation. This concurrently reduces dark current, improves time response, and increases sensitivity in PbS photoconductors, yielding an over-two-fold increase in detectivity.
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A hybrid phototransistor consisting of colloidal PbS quantum dots and few layers of MoS2 (≥2 layers) is demonstrated. The hybrid benefits from tailored light absorption in the quantum dots throughout the visible/near infrared region, efficient charge-carrier separation at the p-n interface, and fast carrier transport through the MoS2 channel. It shows responsivity of up to 10(6) A W(-1) and backgate-dependent sensitivity.
Assuntos
Dissulfetos/química , Equipamentos e Provisões Elétricas , Chumbo/química , Molibdênio/química , Pontos Quânticos , Sulfetos/química , Desenho de Equipamento , Luz , Nanoestruturas/química , Imagem Óptica , Análise Espectral RamanRESUMO
Ultrasmall gold nanoparticles (Au UNPs) represent a unique class of nanomaterials making them very attractive for certain applications. Herein, we developed an organometallic approach to the synthesis of Au UNPs stabilized with the C18H37-NHC ligand by the solvent free thermolysis of [RMIM][Au(C6F5)2] () or [Au(C6F5)(RNHC)] () (with R = C18H37-), by controlling the reactivity of pentafluorophenyl ligands as deprotonating or reductive elimination agents; Au UNPs can be achieved by solvent free thermolysis. Pentafluorophenyl Au(i) complexes and are synthesized from the corresponding ionic and neutral precursors. The presence of long alkyl chain imidazolium or carbene species in the complexes makes them to behave as isotropic liquids at moderate temperatures. The use of multinuclear NMR allows the description of the mechanism of formation of the UNPs as well as the surface state of the UNPs.
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More-efficient charge collection and suppressed trap recombination in colloidal quantum dot (CQD) solar cells is achieved by means of a bulk nano-heterojunction (BNH) structure, in which p-type and n-type materials are blended on the nanometer scale. The improved performance of the BNH devices, compared with that of bilayer devices, is displayed in higher photocurrents and higher open-circuit voltages (resulting from a trap passivation mechanism).
Assuntos
Fontes de Energia Elétrica , Nanotecnologia/instrumentação , Pontos Quânticos/química , Energia Solar , Coloides , Chumbo/química , Soluções , Sulfetos/química , Temperatura , Óxido de Zinco/químicaRESUMO
A simple approach is demonstrated to combine a light trapping scheme and a conductive substrate for solution processed solar cells. By means of soft lithography, a new light-trapping architecture can be integrated as the bottom electrode for emerging thin-film solar-cell technologies without added costs, fully compatible with low-temperature processes, and yielding an enhancement in the photocurrent without altering the rest of the electrical performance of the device.
RESUMO
The polymeric Au/Tl compounds [{Au(C6X5)2}Tl]n (X = Cl, F) react with the crown thioethers 1,4,7-trithiacyclononane ([9]aneS3), 1,5,8,11-tetrathiacyclotetradecane ([14]aneS4), and 1,4,7,10,13,16,19,22-octathiacyclotetracosane ([24]aneS8) in an appropriate molar ratio to afford [{Au(C6X5)2}Tl(L)]2 [L = [9]aneS3, X = Cl (1), F (4); L = [14]aneS4, X = Cl (2), F (5)], [{Au(C6Cl5)2}2Tl2([24]aneS8)]n (3) or [{Au(C6F5)2}2Tl2([24]aneS8)] (6). X-ray diffraction studies of 3, 4 and 6 reveal polymeric (3) or tetranuclear (4, 6) structures formed via Tl-S bonds and AuTl or AuTl and AuAu contacts. All the complexes are luminescent in the solid state, but not in solution, where the metal-metal interactions, which are responsible for the luminescence, are no longer present. DFT calculations on representative model systems of complexes 3, 4 and 6 have also been carried out in order to determine the origin of the electronic transitions responsible for their optical properties.
RESUMO
Heteronuclear complexes {[Hg(R)2][Au(R')(PMe3)]2}n (R=R'=C6Cl2F3 (3); R=R'=C6F5 (4); R=C6Cl2F3, R'=C6F5 (5); R=C6F5, R'=C6Cl2F3 (6)) were prepared by the treatment of the corresponding organomercury compounds, [Hg(C6X5)2], with two equivalents of [Au(C6X5)(PMe3)]. Their crystal structures, as determined by using X-ray diffraction methods, display Au···Hg interactions. Although only compound 4 and 5 show luminescence in the solid state, all of these compounds quench the fluorescence of naphthalene in solution. Solution studies of these derivatives suggest a cooperative effect of the gold(I) center in switching on the quenching capabilities of the [Hg(C6X5)2] synthon with naphthalene. Theoretical studies confirmed the quenching ability of the organomercury species in the presence of gold.
RESUMO
Complex [Au{4-C(6)F(4)(4-C(6)BrF(4))}(tht)] reacts with diphosphines (L-L) such as bis(diphenylphosphino)methane (dppm) or 1,2-bis(diphenylphosphino)benzene (dppb) in a 2 : 1 molar ratio in dichloromethane, leading to neutral products of stoichiometry [(Au{4-C(6)F(4)(4-C(6)BrF(4))})(2)(µ-L-L)] (L-L = dppm (1), dppb (2)). In the crystal structure of complex 2 short Au···Au interactions of 2.9367(5) and 2.9521(5) Å appear. This complex displays an orange emission, which is assigned to arise from a charge transfer transition from a metal centered Au-Au orbital to an orbital located at the diphosphine ligand. Addition of silver trifluoroacetate to these complexes in a 1 : 1 or a 2 : 1 molar ratio generates polymeric heterometallic gold-silver compounds of stoichiometry [Ag(2)Au(2){4-C(6)F(4)(4-C(6)BrF(4))}(2)(CF(3)CO(2))(2)(µ-L-L)](n) (L-L = dppm (3), dppb (4)), which confirms the capability of the neutral [(Au{4-C(6)F(4)(4-C(6)BrF(4))})(2)(µ-diphosphine)] units to act as electron density donors when treated with a Lewis acid substrate. These heterometallic derivatives show blue emissions indicating large HOMO-LUMO band gaps, due to the stabilization that the gold-based HOMO orbitals suffer when the electron withdrawing silver trifluoroacetate fragments interact with them.
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Aiming at the development of new architectures within the context of the quest for strongly luminescent materials with tunable emission, we utilized the propensity of the robust bimetallic clusters [Au2Ag2(R(I)/R(II))4] (R(I) = 4-C6F4I, R(II) = 2-C6F4I) for self-assembly through aurophilic interactions. With a de novo approach that combines the coordination and halogen-bonding potential of aromatic heteroperhalogenated ligands, we have generated a family of remarkably luminescent bimetallic materials that provide grounds to address the relevance, relative effects, and synergistic action of the two interactions in the underlying photophysics. By polymerizing the green-emitting (λ(max)(em) = 540 nm) monomer [Au2Ag2R(II)4(tfa)2]²â» (tfa = trifluoroacetate) to a red-emitting (λ(max)(em) = 660 nm) polymer [Au2Ag2R(II)4(MeCN)2](n), we demonstrate herein that the degree of cluster association in these materials can be effectively and reversibly switched simply by applying mechanochemical and/or vapochemical stimuli in the solid state as well as by solvatochemistry in solution, the reactions being coincident with a dramatic switching of the intense, readily perceptible photoluminescence. We demonstrate that the key event in the related equilibrium is the evolution of a metastable yellow emitter (λ(max)(em) = 580 nm) for which the structure determination in the case of the ligand R(II) revealed a dimeric nonsolvated topology [Au2Ag2R(II)4]2. Taken together, these results reveal a two-stage scenario for the aurophilic-driven self-assembly of the bimetallic clusters [Au2Ag2(R(I)/R(II))4]: (1) initial association of the green-emitting monomers to form metastable yellow-emitting dimers and desolvation followed by (2) resolvation of the dimers and their self-assembly to form a red-emitting linear architecture with delocalized frontier orbitals and a reduced energy gap. The green emission from [Au2Ag2R(II)4(tfa)2]²â» (λ(max)(em) = 540 nm) exceeds the highest energy observed for [Au2Ag2]-based structures to date, thereby expanding the spectral slice for emission from related structures beyond 140 nm, from the green region to the deep-red region.
RESUMO
Complex {[Hg(C(6)F(5))(2)][Au(C(6)F(5))(PMe(3))](2)}(n)2 displays unsupported Au(I)···Hg(II) and Au(I)···Au(I) interactions. Its crystal structure displays a polymeric -(Au-Hg-Au-Au-Hg-Au)(n)- disposition. Ab initio calculations show very strong Au(I)···Hg(II) and Au(I)···Au(I) closed-shell interactions of -73.3 kJ mol(-1) and -57.0 kJ mol(-1), respectively, which have a dispersive (van der Waals) nature and are strengthened by large relativistic effects (>20%).
RESUMO
The luminescence in a series of new bimetallic gold-silver vapochromic structures can be efficiently switched among different colors simply by exposure to solvent vapors. The emission color in these systems is controlled by both aurophilic interactions and halogen bonding, which affect the emission energy through different orbitals.