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1.
Artigo em Inglês | MEDLINE | ID: mdl-32326702

RESUMO

The one-dimensional photovoltaic absorber material Sb2S3 requires crystal orientation engineering to enable efficient carrier transport. In this work, we adopted the vapor transport deposition (VTD) method to fabricate vertically aligned Sb2S3 on a CdS buffer layer. Our work shows that such a preferential vertical orientation arises from the sulfur deficit of the CdS surface, which creates a beneficial bonding environment between exposed Cd2+ dangling bonds and S atoms in the Sb2S3 molecules. The CdS/VTD-Sb2S3 interface recombination is suppressed by such properly aligned ribbons at the interface. Compared to typical [120]-oriented Sb2S3 films deposited on CdS by the rapid thermal evaporation (RTE) method, the VTD-Sb2S3 thin film is highly [211]- and [121]-oriented and the performance of the solar cell is increased considerably. Without using any hole transportation layer, a conversion efficiency of 4.73% is achieved with device structure of indium tin oxide (ITO)/CdS/Sb2S3/Au. This work provides a potential way to obtain vertically aligned thin films on different buffer layers.

2.
Adv Mater ; 31(44): e1904711, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31531905

RESUMO

Scintillators are widely utilized for radiation detections in many fields, such as nondestructive inspection, medical imaging, and space exploration. Lead halide perovskite scintillators have recently received extensive research attention owing to their tunable emission wavelength, low detection limit, and ease of fabrication. However, the low light yields toward X-ray irradiation and the lead toxicity of these perovskites severely restricts their practical application. A novel lead-free halide is presented, namely Rb2 CuBr3 , as a scintillator with exceptionally high light yield. Rb2 CuBr3 exhibits a 1D crystal structure and enjoys strong carrier confinement and near-unity photoluminescence quantum yield (98.6%) in violet emission. The high photoluminescence quantum yield combined with negligible self-absorption from self-trapped exciton emission and strong X-ray absorption capability enables a record high light yield of ≈91056 photons per MeV among perovskite and relative scintillators. Overall, Rb2 CuBr3 provides nontoxicity, high radioluminescence intensity, and good stability, thus laying good foundations for potential application in low-dose radiography.

3.
Small ; 15(44): e1903496, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31489786

RESUMO

Recently, Bi-doped Cs2 Ag0.6 Na0.4 InCl6 lead-free double perovskites demonstrating efficient warm-white emission have been reported. To enable the solution processing and enrich the application fields of this promising material, here a colloidal synthesis of Cs2 Ag1- x Nax In1- y Biy Cl6 nanocrystals is further developed. Different from its bulk states, the emission color temperatures of the nanocrystal can be tuned from 9759.7 to 4429.2 K by Na+ and Bi3+ incorporation. Furthermore, the newly developed nanocrystals can break the wavefunction symmetry of the self-trapped excitons by partial replacement of Ag+ ions with Na+ ions and consequently allow radiative recombination. Assisted with Bi3+ ions doping and ligand passivation, the photoluminescence quantum yield of the Cs2 Ag0.17 Na0.83 In0.88 Bi0.12 Cl6 nanocrystals is further promoted to 64%, which is the highest value for lead-free perovskite nanocrystals at present. The new colloidal nanocrystals with tunable color temperature and efficient photoluminescence are expected to greatly advance the research progress of lead-free perovskites in single-emitter-based white emitting materials and devices.

4.
Sci Rep ; 8(1): 17755, 2018 Dec 10.
Artigo em Inglês | MEDLINE | ID: mdl-30531791

RESUMO

Van der Waals heterostructures composed of two-dimensional (2D) transition metal dichalcogenides (TMD) materials have stimulated tremendous research interest in various device applications, especially in energy-efficient future-generation electronics. Such ultra-thin stacks as tunnel junction theoretically present unprecedented possibilities of tunable relative band alignment and pristine interfaces, which enable significant performance enhancement for steep-slope tunneling transistors. In this work, the optimal 2D-2D heterostructure for tunneling transistors is presented and elaborately engineered, taking into consideration both electric properties and material stability. The key challenges, including band alignment and metal-to-2D semiconductor contact resistances, are optimized separately for integration. By using a new dry transfer technique for the vertical stack, the selected WS2/SnS2 heterostructure-based tunneling transistor is fabricated for the first time, and exhibits superior performance with comparable on-state current and steeper subthreshold slope than conventional FET, as well as on-off current ratio over 106 which is among the highest value of 2D-2D tunneling transistors. A visible negative differential resistance feature is also observed. This work shows the great potential of 2D layered semiconductors for new heterostructure devices and can guide possible development of energy-efficient future-generation electronics.

5.
Nano Lett ; 18(9): 6076-6083, 2018 09 12.
Artigo em Inglês | MEDLINE | ID: mdl-30107746

RESUMO

Metal halide perovskite quantum dots (QDs) recently have attracted great research attentions. However, blue-emitting perovskite QDs generally suffer from low photoluminescence quantum yield (PLQY) because of easily formed defects and insufficient surface passivation. Replacement of lead with low toxicity elements is also preferred toward potential commercial applications. Here, we apply Cl-passivation to boost the PLQY of MA3Bi2Br9 QDs to 54.1% at the wavelength of 422 nm, a new PLQY record for blue emissive, lead-free perovskite QDs. Because of the incompatible crystal structures between MA3Bi2Br9 and MA3Bi2Cl9 and the careful kinetic control during the synthesis, Cl- anions are engineered to mainly locate on the surface of QDs acting as passivating ligands, which effectively suppress surface defects and enhance the PLQY. Our results highlight the potential of MA3Bi2Br9 QDs for applications of phosphors, scintillators, and light-emitting diodes.

6.
Small ; 13(47)2017 12.
Artigo em Inglês | MEDLINE | ID: mdl-29106073

RESUMO

2D halide semiconductors, a new family of 2D materials in addition to transition metal dichalcogenides, present ultralow dark current and high light conversion yield, which hold great potential in photoconductive detectors. Herein, a facile aqueous solution method is developed for the preparation of large-scale 2D lead dihalide nanosheets (PbF2-x Ix ). High-performance UV photodetectors are successfully implemented based on 2D PbF2-x Ix nanosheets. By modulating the components of halogens, the bandgap of PbF2-x Ix nanosheets can be tuned to meet varied detection spectra. The photoresponse dependence on incident power density, wavelength, detection environment, and temperature are systematically studied to investigate their detection mechanism. For PbI2 photodetectors, they are dominantly driven by a photoconduction mechanism and show a fast response speed and a low noise current density. A high normalized detectivity of 1.5 × 1012 Jones and an ION /IOFF ratio up to 103 are reached. On the other hand, PbFI photodetectors demonstrate a photogating mechanism mediated by trap states showing high responsivity. The novel 2D halide materials with wide bandgaps, superior detection performance, and facile synthesis process can enrich the Van der Waals solids family and hold great potential for a wide variety of applications in advanced optoelectronics.

7.
ACS Nano ; 11(9): 9294-9302, 2017 09 26.
Artigo em Inglês | MEDLINE | ID: mdl-28880532

RESUMO

Colloidal quantum dots (QDs) of lead halide perovskite have recently received great attention owing to their remarkable performances in optoelectronic applications. However, their wide applications are hindered from toxic lead element, which is not environment- and consumer-friendly. Herein, we utilized heterovalent substitution of divalent lead (Pb2+) with trivalent antimony (Sb3+) to synthesize stable and brightly luminescent Cs3Sb2Br9 QDs. The lead-free, full-inorganic QDs were fabricated by a modified ligand-assisted reprecipitation strategy. A photoluminescence quantum yield (PLQY) was determined to be 46% at 410 nm, which was superior to that of other reported halide perovskite QDs. The PL enhancement mechanism was unraveled by surface composition derived quantum-well band structure and their large exciton binding energy. The Br-rich surface and the observed 530 meV exciton binding energy were proposed to guarantee the efficient radiative recombination. In addition, we can also tune the inorganic perovskite QD (Cs3Sb2X9) emission wavelength from 370 to 560 nm via anion exchange reactions. The developed full-inorganic lead-free Sb-perovskite QDs with high PLQY and stable emission promise great potential for efficient emission candidates.

8.
Nanoscale ; 9(4): 1567-1574, 2017 Jan 26.
Artigo em Inglês | MEDLINE | ID: mdl-28067929

RESUMO

To date, all the lead halide based full-inorganic or organic-inorganic hybrid perovskites have been synthesized from organic solvent, such as N,N-dimethylformamide (DMF) or dimethyl sulfoxide (DMSO), by a solution method. Herein, water has been utilized as a 'green' solvent to develop an efficient synthetic route to grow various kinds of lead halide perovskite nanowires (NWs). By controlling the proportion of the hybrid cations, Csx(CH3NH3)1-xPbI3 perovskite NWs were successfully synthesized. Every Csx(CH3NH3)1-xPbI3 perovskite NW demonstrated single crystal characteristics with uniform stoichiometric element distribution. Because of the controllable cation composition, the NW bandgaps could be finely tuned from 1.5 to 1.7 eV. Transient photoluminescence spectra showed superior NW quality when compared with those of the conventional DMF-based NWs. Based on the abovementioned high quality single Cs0.5(CH3NH3)0.5PbI3 perovskite NW, a reliable single-NW photodetector was fabricated to investigate the optoelectronic application. It demonstrated a responsivity of 23 A/W, exceeding most of the reported values in the perovskite nanowire photoconductive detectors, and the shot-noise normalized detectivity was 2.5 × 1011 Jones comparable to the parameters of the commercial silicon-based nanowires. The green and robust synthesis method, finely tunable NW bandgaps, and superior optoelectronic properties are expected to open a new door for the development of perovskite optoelectronic devices.

9.
Nanomicro Lett ; 9(3): 36, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-30393731

RESUMO

Metal halide perovskites are crystalline materials originally developed out of scientific curiosity. They have shown great potential as active materials in optoelectronic applications. In the last 6 years, their certified photovoltaic efficiencies have reached 22.1%. Compared to bulk halide perovskites, low-dimensional ones exhibited novel physical properties. The photoluminescence quantum yields of perovskite quantum dots are close to 100%. The external quantum efficiencies and current efficiencies of perovskite quantum dot light-emitting diodes have reached 8% and 43 cd A-1, respectively, and their nanowire lasers show ultralow-threshold room-temperature lasing with emission tunability and ease of synthesis. Perovskite nanowire photodetectors reached a responsivity of 10 A W-1 and a specific normalized detectivity of the order of 1012 Jones. Different from most reported reviews focusing on photovoltaic applications, we summarize the rapid progress in the study of low-dimensional perovskite materials, as well as their promising applications in optoelectronic devices. In particular, we review the wide tunability of fabrication methods and the state-of-the-art research outputs of low-dimensional perovskite optoelectronic devices. Finally, the anticipated challenges and potential for this exciting research are proposed.

10.
Nanomicro Lett ; 9(2): 24, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-30460319

RESUMO

Comparing with hot researches in absorber layer, window layer has attracted less attention in PbS quantum dot solar cells (QD SCs). Actually, the window layer plays a key role in exciton separation, charge drifting, and so on. Herein, ZnO window layer was systematically investigated for its roles in QD SCs performance. The physical mechanism of improved performance was also explored. It was found that the optimized ZnO films with appropriate thickness and doping concentration can balance the optical and electrical properties, and its energy band align well with the absorber layer for efficient charge extraction. Further characterizations demonstrated that the window layer optimization can help to reduce the surface defects, improve the heterojunction quality, as well as extend the depletion width. Compared with the control devices, the optimized devices have obtained an efficiency of 6.7% with an enhanced V oc of 18%, J sc of 21%, FF of 10%, and power conversion efficiency of 58%. The present work suggests a useful strategy to improve the device performance by optimizing the window layer besides the absorber layer.

11.
Nano Lett ; 16(12): 7446-7454, 2016 12 14.
Artigo em Inglês | MEDLINE | ID: mdl-27802046

RESUMO

Photodetectors convert light signals into current or voltage outputs and are widely used for imaging, sensing, and spectroscopy. Perovskite-based photodetectors have shown high sensitivity and fast response due to the unprecedented low recombination loss in this solution processed semiconductor. Among various types of CH3NH3PbI3 morphology (film, single crystal, nanowire), single-crystalline CH3NH3PbI3 nanowires are particularly interesting for photodetection because of their reduced grain boundary, morphological anisotropy, and excellent mechanical flexibility. The concomitant disadvantage associated with the CH3NH3PbI3 nanowire photodetectors is their large surface area, which catalyzes carrier recombination and material decomposition, thus significantly degrading device performance and stability. Here we solved this key problem by introducing oleic acid soaking to passivate surface defects of CH3NH3PbI3 nanowires, which leads to a device with much improved stability and unprecedented sensitivity (measured detectivity of 2 × 1013 Jones). By taking advantage of their one-dimensional geometry, we also showcased, for the first time, the linear dichroic photodetection of our CH3NH3PbI3 nanowire photodetector.

12.
Opt Lett ; 41(12): 2803-6, 2016 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-27304293

RESUMO

Optical antennas enable the control of light-matter interaction on the nanometer scale. Efficient on-chip electrical switching of plasmonic resonances is a crucial step toward the integration of optical antennas into practical optoelectronic circuits. We propose and numerically investigate the on-chip low-voltage linear electrical tuning of a narrowband optical antenna perfect absorber via a piezoelectric optomechanic cavity. Near unity absorption is realized by an array of gold nanostrip antennas separated from a membrane-based deformable backreflector by a small gap. A narrow linewidth of 33 nm at 2.58 µm is realized through the coupling between the plasmonic mode and photonic mode in the cavity-enhanced antenna structure. An aluminum nitride piezoelectric layer enabled efficient actuation of the backreflector and therefore changed the gap size, allowing for the tuning of the spectral absorption. The peak wavelength can be shifted linearly by 250 nm with 10 V of tuning voltage, and the tuning range is not limited by the pull-in effect. The polarization dependence of the nanostrip antenna coupled with the optomechanic cavity allows the use of our device as a voltage tunable polarization control device.

13.
Nanoscale ; 8(13): 7137-43, 2016 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-26965641

RESUMO

Traditional photoconductive photodetectors (PDs) commonly respond to higher energy photons compared with the bandgaps of PD active materials. Different from the wide detection spectra of traditional PDs, the present reported PbS quantum dot (QD) PDs can detect the spectra-selective light source. Spectra-selective PDs (ss-PDs) of perovskite/QDs and QD/QDs were respectively implemented by integrating two functional layers. The top layer (facing the light) was utilized to filter the non-target spectra and the bottom layer was used for detection. The response spectrum wavelength and the range of ss-PDs can be conveniently tailored by tuning the QD size. The obtained selectivity factor and normalized detectivity ratio from target and non-target illumination can reach at least 10. A narrow detection range with a full width at half maximum (FWHM) ∼100 nm was applied by typical QD/QD based ss-PDs. The prototype ss-PDs were successfully applied in identifying an unknown light source. The convenient tuning and identification capabilities of the present QD based ss-PDs may provide a versatile route to obtain highly spectrum-selective PDs in order to meet the demands for special fields.

14.
Light Sci Appl ; 5(7): e16126, 2016 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-30167178

RESUMO

Photodetectors convert photons into current or voltage outputs and are thus widely used for spectroscopy, imaging and sensing. Traditional photodetectors generally show a consistent-polarity response to incident photons within their broadband responsive spectrum. Here we introduced a new type of photodetector employing SnS2 nanosheets sensitized with PbS colloidal quantum dots (CQDs) that are not only sensitive (~105 A W-1) and broadband (300-1000 nm) but also spectrally distinctive, that is, show distinctive (positive or negative) photoresponse toward incident photons of different wavelengths. A careful mechanism study revealed illumination-modulated Schottky contacts between SnS2 nanosheets and Au electrodes, altering the photoresponse polarity toward incident photons of different wavelengths. Finally, we applied our SnS2 nanosheet/PbS CQDs hybrid photodetector to differentiate the color temperature of emission from a series of white light-emitting diodes (LEDs), showcasing the unique application of our novel photodetectors.

15.
ACS Appl Mater Interfaces ; 8(1): 840-6, 2016 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-26652646

RESUMO

Solution-processed SnO2 colloidal quantum dots (CQDs) have emerged as an important new class of gas-sensing materials due to their potential for low-cost and high-throughput fabrication. Here we employed the design strategy based on the synergetic effect from highly sensitive SnO2 CQDs and excellent conductive properties of multiwalled carbon nanotubes (MWCNTs) to overcome the transport barrier in CQD gas sensors. The attachment and coverage of SnO2 CQDs on the MWCNT surfaces were achieved by simply mixing the presynthesized SnO2 CQDs and MWCNTs at room temperature. Compared to the pristine SnO2 CQDs, the sensor based on SnO2 quantum dot/MWCNT nanocomposites exhibited a higher response upon exposure to H2S, and the response toward 50 ppm of H2S at 70 °C was 108 with the response and recovery time being 23 and 44 s. Because of the favorable energy band alignment, the MWCNTs can serve as the acceptor of the electrons that are injected from H2S into SnO2 quantum dots in addition to the charge transport highway to direct the electron flow to the electrode, thereby enhancing the sensor response. Our research results open an easy pathway for developing highly sensitive and low-cost gas sensors.

16.
Nano Lett ; 15(12): 7963-9, 2015 Dec 09.
Artigo em Inglês | MEDLINE | ID: mdl-26529584

RESUMO

Organolead triiodide perovskite (CH3NH3PbI3) as a light-sensitive material has attracted extensive attention in optoelectronics. The reported perovskite photodetectors (PDs) mainly focus on the individual, which limits their spatial imaging applications. Uniform perovskite networks combining transparency and device performance were synthesized on poly(ethylene terephthalate) (PET) by controlling perovskite crystallization. Photodetector arrays based on above network were fabricated to demonstrate the potential for image mapping. The trade-off between the PD performance and transparency was systematically investigated and the optimal device was obtained from 30 wt % precursor concentration. The switching ratio, normalized detectivity, and equivalent dark current derived shot noise as the critical parameters of PD arrays reached 300, 1.02 × 10(12) Jones, and 4.73 × 10(-15)A Hz(-1/2), respectively. Furthermore, the PD arrays could clearly detect spatial light intensity distribution, thus demonstrating its preliminary imaging function. The perovskite network PD arrays fabricated on PET substrates could also conduct superior flexibility under wide angle and large number of bending. For the common problem of perovskite optoelectronics in stability, the perovskite networks sheathed with hydrophobic polymers greatly enhanced the device stability due to the improved interface contacts, surface passivation, and moisture isolation. Taking into consideration transparency, flexibility, imaging and stability, the present PD arrays were expected to be widely applied in visualized portable optoelectronic system.

17.
ACS Appl Mater Interfaces ; 7(45): 25113-20, 2015 Nov 18.
Artigo em Inglês | MEDLINE | ID: mdl-26497670

RESUMO

Organometal halide perovskites have recently emerged as outstanding semiconductors for solid-state optoelectronic devices. Their sensitivity to moisture is one of the biggest barriers to commercialization. In order to identify the effect of moisture in the degradation process, here we combined the in situ electrical resistance measurement with time-resolved X-ray diffraction analysis to investigate the interaction of CH3NH3PbI(3-x)Cl(x) perovskite films with moisture. Upon short-time exposure, the resistance of the perovskite films decreased and it could be fully recovered, which were ascribed to a mere chemisorption of water molecules, followed by the reversible hydration into CH3NH3PbI(3-x)Cl(x)·H2O. Upon long-time exposure, however, the resistance became irreversible due to the decomposition into PbI2. The results demonstrated the formation of monohydrated intermediate phase when the perovskites interacted with moisture. The role of moisture in accelerating the thermal degradation at 85 °C was also demonstrated. Furthermore, our study suggested that the perovskite films with fewer defects may be more inherently resistant to moisture.

18.
Sci Rep ; 5: 8226, 2015 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-25648112

RESUMO

Hierarchical ZnO nanostructures with a large yield were fabricated by a simple thermal evaporation method. For the first time, novel ZnO flowers were observed blooming at certain sites of a variety of spines, identified as Zn-terminated polar (0001) planes or tips. The spines for as-synthesized hierarchical structures can be nanowires, nanobelts, nanodendrites, nanobrushes, etc. This growth phenomenon determines the key role of polar sites in the fabrication of hierarchical structures. The spiral feature of ZnO flowers indicates an unusual screw dislocation driven growth mechanism, which is attributed to a high concentration of Zn vapor.

19.
Nanoscale ; 7(9): 4163-70, 2015 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-25669161

RESUMO

Organolead halide perovskites are becoming intriguing materials applied in optoelectronics. In the present work, organolead iodide perovskite (OIP) nanowires (NWs) have been fabricated by a one step self-assembly method. The controllable NW distributions were implemented by a series of facile techniques: monolayer and small diameter NWs were prepared by precursor concentration tuning; NW patterning was achieved via selected area treatment assisted by a mask; NW alignment was implemented by modified evaporation-induced self-assembly (EISA). The synthesized multifunctional NWs were further applied in photodetectors (PDs) and solar cells as application demos. The PD performances have reached 1.32 AW(-1) for responsivity, 2.5 × 10(12) Jones for detectivity and 0.3 ms for response speed, superior to OIP films and other typical inorganic NW based PD performances. An energy conversion efficiency of ∼2.5% has been obtained for NW film based solar cells. The facile fabrication process, controllable distribution and optoelectronic applications make the OIP NWs promising building blocks for future optoelectronics, especially for low dimensional devices.

20.
Sci Rep ; 4: 6288, 2014 Sep 05.
Artigo em Inglês | MEDLINE | ID: mdl-25190491

RESUMO

To obtain high photovoltaic performances for the emerging copper zinc tin sulfide/selenide (CZTSSe) thin film solar cells, much effort has deservedly been placed on CZTSSe phase purification and CZTSSe grain size enhancement. Another highly crucial but less explored factor for device performance is the elemental constitution of CZTSSe surface, which is at the heart of p-n junction where major photogenerated carriers generate and separate. In this work we demonstrate that, despite the well-built phase and large grained films are observed by common phases and morphology characterization (XRD, Raman and SEM), prominent device efficiency variations from short circuited to 6.4% are obtained. Insight study highlights that the surface (0-250 nm) compositions variation results in different bulk defect depths and doping densities in the depletion zone. We propose that suitable sulfurization (at ~ 10 kPa sulfur pressure) drives optimization of surface constitution by managing the Cu, Zn and Sn diffusion and surface reaction. Therefore, our study reveals that the balance of elemental diffusion and interface reactions is the key to tuning the surface quality CZTSSe film and thus the performance of as resulted devices.

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