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1.
Phys Chem Chem Phys ; 22(3): 981-984, 2020 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-31912822

RESUMO

Herein, we propose a new approach of molecule occupancy via a vapor treatment to facilitate the conversion of PbI2 to perovskite in sequential deposition. We have shown that the morphology of PbI2 and the subsequent crystallization of perovskite can be effectively tuned, thus leading to the elimination of residual PbI2 and promotion of perovskite growth.

2.
Nanoscale ; 12(3): 1448-1454, 2020 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-31829376

RESUMO

Intercalation has proven to be a powerful strategy for physical and chemical property modulation in two dimensional (2D) van der Waals (vdW) materials. Traditional gaseous and chemical intercalation methods offer the ability for mass production, and the electrochemical method provides reversible fine tuning for in situ material investigation. Spatial control, or even direct patterning, of ions is widely required for practical device fabrication and integration; yet it is not realized. Here we demonstrate a self-driven ion (Co2+, Sn4+, and Cu2+) intercalation approach with patterning ability on vdW α-MoO3. It is proved that the self-driven intercalation was enabled by the formation of a local galvanic cell and could be controlled by the metal electrode potential and the solution concentration. The universality of self-intercalation was confirmed in various types of 2D materials (MoS2, WS2, MoSe2, WSe2 and graphene). Furthermore, the feasibility of building heterostructures by multiple species (Sn & Co) intercalation in a single nanosheet was demonstrated for broadband photodetection. The enhancement of conductivity and photoresponse was found to be due to the synergistic effect of lattice distortion from Sn intercalation and the d orbital from the Co atom. This approach offers a feasible way for direct nano-fabrication in 2D vdW material and functional device integration.

3.
ACS Appl Mater Interfaces ; 11(17): 15741-15747, 2019 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-30920195

RESUMO

Defects engineering can broaden the absorption band of wide band gap van der Waals (vdW) materials to the visible or near-IR regime at the expense of material stability and photoresponse speed. Herein, we introduce an atomic intercalation method that brings the wide band gap vdW α-MoO3 for vis-MIR broadband optoelectronic conversion. We confirm experimentally that intercalation significantly enhances photoabsorption and electrical conductivity buts effects negligible change to the lattice structure as compared with ion intercalation. Charge transfer from the Sn atom to the lattices induces an optoelectrical change. As a result, the Sn-intercalated α-MoO3 shows room temperature, air stable, broadband photodetection ability from 405 nm to 10 µm, with photoresponsivity better than 9.0 A W-1 in 405-1500 nm, ∼0.4 A W-1 at 3700 nm, and 0.16 A W-1 at 10 µm, response time of ∼0.1 s, and peak D* of 7.3 × 107 cm Hz0.5 W-1 at 520 nm. We further reveal that photothermal effect dominates in our detection range by real-time photothermal-electrical measurement, and the materials show a high temperature coefficient of resistance value of -1.658% K-1 at 300 K. These results provide feasible route for designing broadband absorption materials for photoelectrical, photothermal, or thermal-electrical application.

4.
Materials (Basel) ; 11(5)2018 May 09.
Artigo em Inglês | MEDLINE | ID: mdl-29747404

RESUMO

Solution approaches to NiOx films for electrochromic applications are problematic due to the need of an additional high-temperature annealing treatment step in inert gas. In this study, nanostructured NiOx powder with grain size of about 10.1 nm was synthesized for fabrication of NiOx films for electrochromic application. Non-toxic dispersants of isopropanol and deionized water were used and the whole process was carried out in air. The effects of the number of spin-coating layers, annealing temperature, and the volume ratios of isopropanol to deionized water were systematically investigated. Large transmittance change of 62.3% at 550 nm, high coloration efficiency (42.8 cm²/C), rapid switching time (coloring time is 4 s, bleaching time is 3 s), and good stability were achieved in the optimized NiOx film. The optimized process only required a low processing temperature of 150 °C in air with spin-coating three times and 1:2 volume ratio of isopropanol to deionized water. Finally, good cycle durability of up to 2000 cycles without obvious degradation was demonstrated by cyclic voltammetry tests in a LiClO4/propylene carbonate electrolyte. This study provides a simple and effective approach for fabrication of NiOx films at low temperature in air, which is attractive for further commercialization of electrochromic devices.

5.
Adv Mater ; 30(13): e1705318, 2018 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-29469218

RESUMO

2D van der Waals (vdW) layered polar crystals sustaining phonon polaritons (PhPs) have opened up new avenues for fundamental research and optoelectronic applications in the mid-infrared to terahertz ranges. To date, 2D vdW crystals with PhPs are only experimentally demonstrated in hexagonal boron nitride (hBN) slabs. For optoelectronic and active photonic applications, semiconductors with tunable charges, finite conductivity, and moderate bandgaps are preferred. Here, PhPs are demonstrated with low loss and ultrahigh electromagnetic field confinements in semiconducting vdW α-MoO3 . The α-MoO3 supports strong hyperbolic PhPs in the mid-infrared range, with a damping rate as low as 0.08. The electromagnetic confinements can reach ≈λ0 /120, which can be tailored by altering the thicknesses of the α-MoO3 2D flakes. Furthermore, spatial control over the PhPs is achieved with a metal-ion-intercalation strategy. The results demonstrate α-MoO3 as a new platform for studying hyperbolic PhPs with tunability, which enable switchable mid-infrared nanophotonic devices.

6.
ACS Appl Mater Interfaces ; 9(6): 5543-5549, 2017 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-28116901

RESUMO

Layered α-MoO3 is a multifunctional material that has significant application in optoelectronic devices. In this study, we show the growth of large-scale, large-size, few-layered (FL) α-MoO3 nanosheet directly on technical substrates (SiO2 and Si) by physical vapor deposition. We suggest that the growth is self-limiting in the [010] direction because of the re-evaporation and high diffusion capacity of MoOx species at high temperature. As-prepared FL α-MoO3 is nonconductive and shows poor response to photoillumination with wavelength of 405 and 630 nm. Its work function is strongly altered by the substrate. Improvement of conductivity and photoresponse is observed after the FL device is annealed in vacuum. Line defects along the [001], [100], and [101] directions belonging to the generation of Os and Oa vacancy states appear, and the interfacial effect is suppressed. Scanning near-field optical microscope shows that the defects are absorption sites. Kelvin probe force microscope reveals decrease of apparent work function under illumination, which confirms that electrons are excited from defects states. Our findings show that intense studies on defect engineering are required to push forward the application of two-dimensional metal oxides.

7.
ACS Appl Mater Interfaces ; 8(47): 32366-32375, 2016 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-27933852

RESUMO

Quantification of intergrain length scale properties of CH3NH3PbI3 (MAPbI3) can provide further understanding of material physics, leading to improved device performance. In this work, we noticed that two typical types of facets appear in sequential deposited perovskite (SDP) films: smooth and steplike morphologies. By mapping the surface potential as well as the photoluminescence (PL) peak position, we revealed the heterogeneity of SDP thin films that smooth facets are almost intrinsic with a PL peak at 775 nm, while the steplike facets are p-type-doped with 5-nm blue-shifted PL peak. Considering the reaction process, we propose that the smooth facets have well-defined crystal lattices that resulted from the interfacial reaction between MAI and PbI2 domains containing low trap states density. The steplike facets are MAI-rich originated from the grain boundaries of PbI2 film and own more trap states. Conversion of steplike facets to smooth facets can be controlled by increasing the reaction time through Ostwald ripening. The improved stability, photoresponsivity up to 0.3 A/W, on/off ratio up to 3900, and decreased photo response time to ∼160 µs show that the trap states can be annihilated effectively to improve the photoelectrical conversion with prolonged reaction time and elimination of steplike facets. Our findings demonstrate the relationship between the facet heterogeneity of SDP films and crystal growth process for the first time, and imply that the systematic control of crystal grain modification will enable amelioration of crystallinity for more-efficient perovskite photoelectrical applications.

8.
ACS Appl Mater Interfaces ; 8(29): 19158-67, 2016 Jul 27.
Artigo em Inglês | MEDLINE | ID: mdl-27391382

RESUMO

UNLABELLED: Organic-inorganic hybrid heterojunctions are poised to push toward novel optoelectronics applications, such as photodetectors, but significant challenges complicating practical use remain. Although all organic based photodetectors have been reported with great success, their potential in high-speed, broadband, self-powered photodetectors have not been fully explored. Herein, a self-powered, broad bandwidth of photodetector based on PEDOT: PSS/Si heterojunction is built by a facial low temperature spin-coating method. By interface engineering of heterojunction with optimal band alignment and heteromicrostructures, enhanced photoresponse performances are obtained. The bandwidth of the hybrid photodetector could be broadened by 10 kHz after interfacial passivation by a methyl group. Further manipulating the geometrical structure of the hybrid heterojunction with silicon nanowire, a broad spectrum response from 300 to 1100 nm, with bandwidth as high as 40.6 kHz, fast response speed of 2.03 µs and high detection of 4.1 × 10(11) Jones under zero bias was achieved. Meanwhile, the close dependence between the photoresponse performance of heterojunctions and Si nanowire length is observed in the top-coverage configuration. Finally, a coverage effects model is proposed based on the competition of Si bulk and surface recombination, which is also confirmed by the designed bottom-coverage experiment. The mechanisms behind the enhanced photoresponse of the hybrid photodetector is attributed to the optimum band alignment, as well as the optimum balance of carrier dissociation and recombination of heterojunction. The scalable and low temperature method would be of great convenience for large-scale fabrication of the PEDOT: PSS/Si hybrid photodetector.

9.
ACS Nano ; 10(1): 1662-70, 2016 Jan 26.
Artigo em Inglês | MEDLINE | ID: mdl-26689113

RESUMO

The hydrogenation process of the layered α-MoO3 crystal was investigated on a nanoscale. At low hydrogen concentration, the hydrogenation can lead to formation of HxMoO3 without breaking the MoO3 atomic flat surface. For hydrogenation with high hydrogen concentration, hydrogen atoms accumulated along the <101> direction on the MoO3, which induced the formation of oxygen vacancy line defects. The injected hydrogen atoms acted as electron donors to increase electrical conductivity of the MoO3. Near-field optical measurements indicated that both of the HxMoO3 and oxygen vacancies were responsible for the coloration of the hydrogenated MoO3, with the latter contributing dominantly. On the other hand, diffusion of hydrogen atoms from the surface into the body of the MoO3 will encounter a surface diffusion energy barrier, which was for the first time measured to be around 80 meV. The energy barrier also sets an upper limit for the amount of hydrogen atoms that can be bound locally inside the MoO3 via hydrogenation. We believe that our findings has provided a clear picture of the hydrogenation mechanisms in layered transition-metal oxides, which will be helpful for control of their optoelectronic properties via hydrogenation.

10.
ACS Appl Mater Interfaces ; 7(46): 25981-90, 2015 Nov 25.
Artigo em Inglês | MEDLINE | ID: mdl-26544078

RESUMO

Photodetectors with a wide spectrum response are important components for sensing, imaging, and other optoelectronic applications. A molybdenum oxide (MoO(3-x))/Si heterojunction has been applied as solar cells with great success, but its potential in photodetectors has not been explored yet. Herein, a self-powered, high-speed heterojunction photodetector fabricated by coating an n-type Si hierarchical structure with an ultrathin hole-selective layer of molybdenum oxide (MoO(3-x)) is first investigated. Excellent and stable photoresponse performance is obtained by using a methyl group passivated interface. The heterojunction photodetector demonstrated high sensitivity to a wide spectrum from 300 to 1100 nm. The self-powered photodetector shows a high detectivity of (∼6.29 × 10(12) cmHz(1/2) W(-1)) and fast response time (1.0 µs). The excellent photodetecting performance is attributed to the enhanced interfacial barrier height and three-dimensional geometry of Si nanostructures, which is beneficial for efficient photocarrier collection and transportation. Finally, our devices show excellent long-term stability in air for 6 months with negligible performance degradation. The thermal evaporation method for large-scale fabrication of MoO(3-x)/n-Si photodetectors makes it suitable for self-powered, multispectral, and high-speed response photodetecting applications.

11.
Phys Chem Chem Phys ; 17(41): 27409-13, 2015 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-26422643

RESUMO

The interfacial reaction and energy level alignment at the Si/transition metal oxide (TMO, including MoO3-x, V2O5-x, WO3-x) heterojunction are systematically investigated. We confirm that the interfacial reaction appears during the thermal deposition of TMO, with the reaction extent increasing from MoO3-x, to V2O5-x, and to WO3-x. The reaction causes the surface oxidation of silicon for faster electron/hole recombination, and the reduction of TMO for effective hole collection. The photovoltaic performance of the Si/TMO heterojunction devices is affected by the interface reaction. MoO3-x are the best hole selecting materials that induce least surface oxidation but strongest reduction. Compared with H-passivation, methyl group passivation is an effective way to reduce the interface reaction and improve the interfacial energy level alignment for better electron and hole collection.

12.
ACS Appl Mater Interfaces ; 7(10): 5830-6, 2015 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-25711433

RESUMO

The interfacial energy-level alignment of a silicon nanowires (SiNWs)/PEDOT:PSS heterojunction is investigated using Kelvin probe force microscopy. The potential difference and electrical distribution in the junction are systematically revealed. When the PEDOT:PSS layer is covered at the bottom of the SiNW array, an abrupt junction is formed at the interface whose characteristics are mainly determined by the uniformly doped Si bulk. When the PEDOT:PSS layer is covered on the top, a hyperabrupt junction localized at the top of the SiNWs forms, and this characteristic depends on the surface properties of the SiNWs. Because the calculation shows that the absorption of light from the SiNWs and the Si bulk are equally important, the bottom-coverage structure leads to better position matching between the depletion and absorption area and therefore shows better photovoltaic performance. The dependence of JSC and VOC on the junction characteristic is discussed.

13.
Nanotechnology ; 24(43): 435403, 2013 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-24107414

RESUMO

Self-powered systems usually consist of energy-acquisition components, energy-storage components and functional components. The development of nanoscience and nanotechnology has greatly improved the performance of all the components of self-powered systems. However, huge differences in the materials and configurations in the components cause large difficulties for integration and miniaturization of self-powered systems. Design and fabrication of different components in a self-powered system with the same or similar materials/configurations should be able to make the above goal easier. In this work, a proof-of-concept experiment involving an integrated self-powered color-changing system consisting of TiO2 nanowire based sandwich dye-sensitized solar cells (DSSCs) and electrochromic devices (ECDs) is designed and demonstrated. When sunlight illuminates the entire system, the DSSCs generate electrical power and turn the ECD to a darker color, dimming the light; by switching the connection polarity of the DSSCs, the lighter color can be regained, implying the potential application of this self-powered color-changing system for next generation sun glasses and smart windows.

14.
Sci Rep ; 3: 2756, 2013 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-24067743

RESUMO

VO2 (M) STF through reduction of V2O5 STF was prepared. The results illustrate that V2O5 STF can be successfully obtained by oblique angle thermal evaporation technique. After annealing at 550 °C/3 min, the V2O5 STF deposited at 85° can be easily transformed into VO2 STF with slanted columnar structure and superior thermochromic properties. After deposition SiO2 antireflective layer, Tlum of VO2 STF is enhanced 26% and ΔTsol increases 60% compared with that of normal VO2 thin films. Due to the anisotropic microstructure of VO2 STF, angular selectivity transmission of VO2 STF is observed and the solar modulation ability is further improved from 7.2% to 8.7% when light is along columnar direction. Moreover, the phase transition temperature of VO2 STF can be depressed into 54.5 °C without doping. Considering the oblique incidence of sunlight on windows, VO2 STF is more beneficial for practical application as smart windows compared with normal homogenous VO2 thin films.

15.
ACS Appl Mater Interfaces ; 5(11): 4960-5, 2013 Jun 12.
Artigo em Inglês | MEDLINE | ID: mdl-23639244

RESUMO

The interfacial transport properties and density of states (DOS) of CuPc near the dielectric surface in an operating organic field-effect transistor (OFET) are investigated using Kelvin probe force microscopy. We find that the carrier mobility of CuPc on high-k Al2Oy/TiOx (ATO) dielectrics under a channel electrical field of 4.3 × 10(2) V/cm reaches 20 times as large as that of CuPc on SiO2. The DOS of the highest occupied molecular orbital (HOMO) of CuPc on the ATO substrate has a Gaussian width of 0.33 ± 0.02 eV, and the traps DOS in the gap of CuPc on the ATO substrate is as small as 7 × 10(17) cm(-3). A gap state near the HOMO edge is observed and assigned to the doping level of oxygen. The measured HOMO DOS of CuPc on SiO2 decreases abruptly near E(V(GS) = V(T)), and the pinning of DOS is observed, suggesting a higher trap DOS of 10(19)-10(20) cm(-3) at the interface. The relationships between DOS and the structural, chemical, as well as electrical properties at the interface are discussed. The superior performance of CuPc/ATO OFET is attributed to the low trap DOS and doping effect.

16.
ACS Nano ; 7(3): 2617-26, 2013 Mar 26.
Artigo em Inglês | MEDLINE | ID: mdl-23368853

RESUMO

Although MnO2 is a promising material for supercapacitors (SCs) due to its excellent electrochemical performance and natural abundance, its wide application is limited by poor electrical conductivity. Inspired by our results that the electrochemical activity and electrical conductivity of ZnO nanowires were greatly improved after hydrogenation, we designed and fabricated hydrogenated single-crystal ZnO@amorphous ZnO-doped MnO2 core-shell nanocables (HZM) on carbon cloth as SC electrodes, showing excellent performance such as areal capacitance of 138.7 mF/cm(2) and specific capacitance of 1260.9 F/g. Highly flexible all-solid-state SCs were subsequently assembled with these novel HZM electrodes using polyvinyl alcohol/LiCl electrolyte. The working devices achieved very high total areal capacitance of 26 mF/cm(2) and retained 87.5% of the original capacitance even after 10 000 charge/discharge cycles. An integrated power pack incorporating series-wound SCs and dye-sensitized solar cells was demonstrated for stand-alone self-powered systems.

17.
Phys Chem Chem Phys ; 14(46): 16111-4, 2012 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-23108069

RESUMO

Compared to the p-n junction type device (Device A) with an n-type ZnO nanowire (n-ZnO)/p-type silicon (p-Si) hybrid structure, the newly designed device (Device B) with an n-ZnO/reduced graphene oxide sheet (rGO)/p-Si hybrid structure displays interesting electrical characteristics such as lower turn-on voltage and better current symmetry. The addition of rGO between n-ZnO and the p-Si substrate enables tuning of the p-n junctions into back-to-back Schottky junctions and lowering of the turn-on voltages, implying great potential applications in electronic and optoelectronic devices. The electrical characteristics and operating mechanism of these two devices are fully discussed.

18.
Nanoscale ; 4(18): 5755-60, 2012 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-22895660

RESUMO

In this work, we report on the detailed characterization and mechanism analysis of the improved wettability performance of a new type of ZnO nanostructure, the ultrathin ZnO nanotube, whose growth is induced by screw-dislocation. The newly discovered enhanced wettability properties are suggested to be caused by coupling the morphology and size effects of the nanostructured surface. These ultrathin nanotubes with low density and small dimension form a wet-hair-like hierarchical morphology, which shows a further improved superhydrophobic property with an 8.6 ± 1.6° larger contact angle than that of ZnO nanorods due to the morphology effect. In addition, owing to the large surface to volume ratio and increased effective UV-irradiated area of the ultrathin tubular structure, the ZnO nanotubes exhibit ∼5 times faster superhydrophobicity to superhydrophilicity conversion speed than nanorods under 254 nm UV illumination. Furthermore, UV light with a wavelength of 254 nm exhibits ∼40 times faster wettability conversion speed for nanotubes than that of 365 nm, which is suggested to be a result of the band gap shift at the nanoscale. The combined advantages of enhanced superhydrophobicity, improved sensitivity, and faster conversion speed by coupling morphology and size effects of these ZnO nanotubes should give them broad applications in self-cleaning surfaces and wettability switches.

19.
Appl Opt ; 51(23): 5718-23, 2012 Aug 10.
Artigo em Inglês | MEDLINE | ID: mdl-22885586

RESUMO

Optical modeling based on the transfer matrix method is employed to investigate the performance of the organic planar heterojunction solar cell with rubrene/C70 as the active layer. The detailed investigation is directed into the effects of layer thickness of the rubrene and C70 on the total absorbed photon density in the active layer. It is revealed that the optical interference plays important role in the performance of the device and the optimal device performance is achieved when the thicknesses of the rubrene and C70 are set as 33 and 28 nm. The simulated results are also confirmed by the experimental data.

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