Electrochromic Photodetectors: Toward Smarter Glasses and Nano

Subscriber access provided by UNIV OF SOUTHERN INDIANA

Functional Inorganic Materials and Devices

Electrochromic photodetectors: toward smarter glasses and nano reflective displays via an electrolytic mechanism Zhenyin Hai, Mohammad Karbalaei Akbari, Zihan Wei, Jasper Zuallaert, Wesley De Neve, Chenyang Xue, Hongyan Xu, Francis Verpoort, and Serge Zhuiykov ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b06555 • Publication Date (Web): 15 Jul 2019 Downloaded from pubs.acs.org on July 17, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Electrochromic photodetectors: toward smarter glasses and nano reflective displays via an electrolytic mechanism Zhenyin Hai,*,†,‡ Mohammad Karbalaei Akbari,†,‡ Zihan Wei,†,‡ Jasper Zuallaert,§,∥ Wesley De Neve,§,∥ Chenyang Xue,⊥ Hongyan Xu,¶ Francis Verpoort,#,∇ and Serge Zhuiykov*,†,‡ †Center

for Environmental & Energy Research, Ghent University Global Campus, Incheon

21985, South Korea ‡Department §Center

of Green Chemistry and Technology, Ghent University, Ghent 9000, Belgium

for Biotech Data Science, Ghent University Global Campus, Incheon 21985, South

Korea ∥IDLab,

Department for Electronics and Information Systems, Ghent University, Ghent 9000,

Belgium ⊥Key

Laboratory of Instrumentation Science and Dynamic Measurement of Ministry of

Education, North University of China, Taiyuan 030051, P.R. China ¶School

of Materials Science and Engineering, North University of China, Taiyuan 030051, P.R.

China #National

Research Tomsk Polytechnic University, Tomsk 634050, Russian Federation

ACS Paragon Plus Environment

1

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

∇State

Page 2 of 26

Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan

University of Technology, Wuhan 430070, P.R. China

ABSTRACT: Electrochromic devices, serving as smart glasses, have not yet been intelligent enough to regulate lighting conditions independent of external photosensing devices. On the other hand, their bulky sandwich structures have been suffering setbacks utilized for reflective displays in an effort to compete with mature emissive displays. The key to resolve both problems lies in incorporating photosensing function into electrochromic devices while simplifying their configuration via replacing ionic electrolytes. However, so far it has not yet been achieved owing to the essential operating difference between the optoelectronic devices and the ionic devices. Herein, a concept of a smarter and thinner device: “electrochromic photodetector” is proposed to solve such problems. It is all-solid-state and electrolyte-free and operates with a simple thin Metal-Semiconductor-Metal (MSM) structure via an electrolytic mechanism. As a proof of concept, a configuration of electrochromic photodetector is presented in this work based on a tungsten trioxide (WO3) thin film deposited on Au electrodes via facile, low-cost solution processes. The electrochromic photodetector switches between its photosensing and electrochromic functions via voltage modulation within 5 V, which is the result of semiconductor-metal transition. The transition mechanism is further analyzed to be the voltagetriggered reversible oxygen/water vapor adsorption/intercalation from ambient air.

KEYWORDS: electrochromic, photodetectors, tungsten oxide, smart glasses, reflective display


2

Page 3 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION As the request for nanomaterials to be more intelligent and multifunctional, the electrochromic materials, such as tungsten trioxide (WO3), molybdenum trioxide (MoO3) and vanadium pentoxide (V2O5), have been intensively investigated to fabricate smart windows for sunlight regulation as well as explored for reflective displays against the mature liquid crystal /organic light-emitting diode-based emissive displays.1–5 So far, the electrochromic devices with high contrast and fast switching have been achieved.6,7 However,

the

realization

method

of

electrochromism,

depending

on

intercalation/deintercalation of ions such as H+, Li+ and Na+ commonly from liquid or gel electrolyte, still limits their performance improvements and applications.8,9 On one hand, the resulted bulky sandwich-like structure containing electrolyte severely obstructs the investigation of operation mechanism, as the in-situ examination to directly disclose the structural transition and ion migration processes is nearly out of the question. On the other hand, the bulky structure also hinders the miniaturization of the devices and thus restricts their application in Micro/NanoOpto-Electro-Mechanical Systems. Besides, the evolved electrochromic devices with adoption of organic active materials9 and introduction of solid-state ionic conductors10 are still under exploration, suffering from instability and slow switching speed. Moreover, as the main application of electrochromic devices, the smart glasses are yet not intelligent enough to adjust light transmittance on their own. Further integration of electrochromic devices with photodetectors would increase their complexity and cost of the systems. Herein, we propose the alternative concept of “electrochromic photodetector”, in which electrochromism and photodetection are realized within one simple all-solid-state, electrolytefree Metal-Semiconductor-Metal (MSM) structure and modulated via low bias voltage. The


3


Page 4 of 26

electrochromic photodetector functions as both light sensor and light actuator. It could automatically process light information independently according to the preset request, which is critical to the hardware realization of artificial intelligence. As a proof of concept, we use WO3 as an active material. The electrochromism of WO3 is explained by WO3|transparent + x(M+ + e-) ↔ MxWO3|blue, where M is either an alkali metal or hydrogen.11–16 The M+ ions contained in the liquid or gel electrolyte insert into/extract out the adjacent WO3 layer driven by bias voltage applied through two outer transparent electrodes. On the other side, WO3, as an n-type semiconductor with widely tunable optical bandgap of ca. 2.53.7 eV,17–23 has also gradually captured the attention for visible-blind UV-A photodetectors.24–28 WO3 photodetector could operate through adopting simple MSM structure under very low voltage. Therefore, combining WO3 electrochromism together with UV-A photoresponse properties into one device would window more functionalities for practical outdoor smart glasses and reflective displays. Consequently, we present the MSM structure WO3 electrochromic photodetector. The electrochromic photodetector was constructed with microwave-exfoliated WO3 nanosheets coated on Au electrode via solution process. The electrochromic photodetector switches between its photodetection and electrochromism functions via low voltage modulation. The operating mechanism is analyzed to be the voltage-triggered reversible oxygen/water vapor adsorption/intercalation from ambient air. The proposed all-solid-state, electrolyte-free electrochromic photodetector based on the electrolytic operation mechanism offers a unique pathway for further development of smarter, smaller, cheaper, and better-performing electrochromic devices.


4

Page 5 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


RESULTS AND DISCUSSION As schematically presented in Figure 1a, the electrochromic photodetector is based on microwave-exfoliated WO3 nanosheets, which were drop-casted on Al2O3 substrate with Au interdigitated electrodes. The WO3 electrochromic photodetector was stabilized via keeping substrate temperature of 380 °C for four hours before any test taken place. The detailed fabrication process is described in the Experimental Section. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) characterizations at a typical surface region indicated the relatively uniform dispersion of WO3 nanosheets on the whole target surface (Figure 1b). The SEM images in Figure S1 clearly depict that the WO3 film on Al2O3 substrate was comprised of nanosheets aggregating together after annealing. The thickness of the film was measured to be around 1 μm as displayed in Figure 1c. X-ray diffraction (XRD) pattern of the sample confirmed the monoclinic crystal structure of the annealed WO3 film (ICSD #80056) with no other WO3 crystal phase accompanied except Au metal electrode and α-Al2O3 substrate (Figure 1d). The monoclinic WO3 is the most stable phase of WO3 as indicated by its threedimensional (3D) network structure (Figure S2). Due to the resolution limit of EDS and XRD, X-ray Photoelectron Spectrometer (XPS) was further adopted to examine the chemical components of the sample. The high-resolution W 4f was deconvoluted into two main peaks W 4f5/2 (38.0 eV) and W 4f7/2 (35.9 eV), representative of the W element with an oxidation state of +6 (Figure 1e).29 Two small peaks located at 36.7 and 35.0 eV were attributed to the inevitable formation of few W5+ defects in the crystal structure under the facile and relatively lowtemperature annealing process.30 The as-prepared WO3 film should be precisely expressed as WO2.954, calculated from the area ratio of W6+ and W5+.31 Moreover, the XPS results pointed out the existence of the trace elements in the commercial substrate (Figure S3). Nevertheless, such a


5


Page 6 of 26

few defects and trace elements would not have a dominant influence on the performances of the samples.

Figure 1. Fabrication and characterization of the WO3 electrochromic photodetector. a) Schematic of the WO3 electrochromic photodetector on Al2O3 substrate. b) SEM image of a typical region indicated in a) and the corresponding EDS mapping results. c) Cross-sectional SEM image of WO3 film on Al2O3 substrate. d) XRD characterization of the device. e) Highresolution XPS spectrum of W 4f. f) UV-vis absorption spectrum of the WO3 film. Inset: plot of (αhν)0.5 against hν.

As the simple Au-WO3-Au MSM configuration was verified through the above measurements, the optical properties of the WO3 film, which is of great importance for the electrochromic photodetectors, were investigated via UV-vis spectra. The absorption spectrum in Figure 1f exhibited pronounced absorption edge at ca. 450 nm, corresponding to an optical


6

Page 7 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


bandgap of 2.76 eV for WO3 shown in the Inset of Figure 1f. The transmittance spectrum demonstrated extremely high visible light transparency of the prepared WO3 film (Figure S4a). The thin film also led to relatively high light transmittance in the UV range. Nevertheless, the optical bandgap and UV-vis transmittance of the film were found to be able to be tuned through thickness variation as presented in Figure S4. The optical bandgap increased to 2.83 eV in the thicker film while the light transmittance in most of the visible range decreased and the UV transmittance at 365 nm dropped sharply. This WO3 film with tunable optical properties could be further optimized for electrochromic photodetectors in response to different applications demand. The performances of the device based on the above-characterized WO3 film were measured as a demonstration of the operation modes of the proposed electrochromic photodetector. Cyclic Voltammetry (CV) test was initially conducted to investigate the electrical characteristics of the devices without UV illumination. As shown in Figure 2a and Figure S5, three typical CV curves displayed nearly symmetric patterns over the center at 0 V, which are highly distinguishable from those capacitive features of the conventional electrochromic devices.3,13,32 The electrical behaviors of the electrochromic photodetector also differ from those of the memristors,33–37 which follow classic “8”-shape loops with memory effects. The electrochromic photodetector obeys the same loop direction in both positive and negative voltages, indicating an entirely distinct operation mechanism. The current underwent steep increment at around 4 V as voltage scanned to higher value and displayed prominent hysteresis when voltage swept back. The CV curves evidently revealed the semiconductor-metal transition of WO3 under such a simple MSM structure, which offers a fresh new configuration for the generation of electrochromism.38–40 The linear region in the CV curves within ca. 3 V as presented in Figure 2b appeared to indicate the characteristics of linear resistors and thus implied the high stability of WO3 under such a voltage


7


Page 8 of 26

range. This makes multi-functionalization of electrochromic devices via voltage modulation possible, and therefore, on which the proposed electrochromic photodetectors toward outdoor smarter glasses and reflective displays were based. The weak humps near 0 V, attributed to the small capacitance induced by the interdigitated electrode employed in the device, could be minimalized through optimization design of electrode.

Figure 2. Voltage modulation of the electrochromic photodetector. a) CV characteristics of the device between ±5 V at a scan rate of 100 mV s-1 without UV illumination. b) The linear region of the CV curves. c) Time-dependent current response of the device under different voltages with UV illumination after 2k seconds. d) The response time of the current to voltage modulation.


8

Page 9 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The voltage modulation of the electrochromic photodetector within 5 V was further expounded through the time-dependent current response to voltage and UV illumination in Figure 2c. With the applied voltage less than 3 V, the current values stabilized below 1 μA and exhibited distinct photoresponsivity especially at 1 V while 365 nm UV illumination was on from around the 2000th second. This voltage region is feasible for photodetection, which will be elaborated in the following figure. Once the voltage is above 3 V, particularly reaching 5 V, the current will attain mA level, consequently transforming the active material into metallic state and exhibiting no photoresponse worthy of exploration. In addition, the device in both states was verified to have no observable response for indoor ambient light or daily lighting except the direct sunlight. This is in accordance with the above-mentioned UV-vis spectra characterization of WO3. However, the electrochromic photodetector could be tailored to response to the visible light for specific applications. Another performance metric for the electrochromic photodetector as a multifunctional device is the switching time. The response time of the current to the voltage modulation has yet been unsatisfying as indicated in Figure 2d. Despite of conspicuous changes within the first few seconds upon the applied voltages excluding the state transition voltage approximately ranging from 3 V to 4 V, the current experienced long stabilization processes, reaching a relatively stable stage at around tens to hundreds of seconds. Nevertheless, the switching time of electrochromic photodetector is able to be improved based on the following detailed investigation of the photoresponse and electrochromic performances of the device. Figure 3 displays the photoresponse performance metrics of the device. The photoresponse of the device under 365 nm UV illumination reached its peak within ca. 0.6-1.2 V and severely decayed after ca. 2 V with higher current instability for both positive and negative voltage ranges as presented in Figure 3a and Figure S6a, respectively. The device also possessed very low dark


9


Page 10 of 26

current. The photoswitching behaviors under the five typical positive voltages shown in Figure 3b represent the performance evolvement of the device while the full tests results with different applied voltages within 3 V were given in Figure S7. For the positive applied voltage range, the photocurrent ascended sharply and the response time improved as well when the voltage increased up to 0.8 V. Within the voltage range of ca. 0.8-2 V, the photocurrent decreased whereas the response time kept improving. This may result from the voltage-triggered defects generated in the WO3 thin film under the relative higher voltage over 0.8 V. Subsequently, the current started suffering from increasing turbulences after 2 V accompanying by photoresponse degeneration due to the local structural transformation. Whilst the applied voltage approached to 3 V, the semiconductor-metal transition of the WO3 film could be triggered although hours may need to take. The photoresponse evolvements in the negative voltage range were practically identical to those mentioned above.

Figure 3. Photoresponse performances of the electrochromic photodetector. a) UV light response of the device within 3 V. b) The representative photoswitching tests of the device under the


10

Page 11 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


typical voltages. c) The responsivity, d) response time, e) detectivity, and f) ON/OFF ratio of the device under UV illumination.

As demonstrated in Figure 3c-f and Figure S6b, the device maintained comparably superior performances within the voltage range of ca. 0.6-1.2 V in terms of all figures of merit. The optimal values obtained within the voltage range for the device were 17.5 μA W-1 @ 0.8 V, 5.9×10-3 % @ 0.8 V, 10.2 s/30.2 s @-0.6 V/-0.8 V, 77.5 M Jones @ 0.8 V, 4.7 @ -0.6 V with respect to responsivity, external quantum efficiency (EQE), response time, detectivity and ON/OFF ratio, correspondingly. Moreover, the response time of the device under applied voltage of near 2 V could reach to almost one second, even though other performances were rather low. The detailed testing conditions and calculation methods can be found in the Experimental Section and Supporting Information. The determinants of photoresponse performances in the electrochromic photodetector will be discussed combining with the evidences observed from the electrochromic processes depicted in the subsequent figures. Concerning the power consumption of the device, the nA level working current with the small bias voltage suggested the ultralow energy dissipation for photodetection. Compared to the other newly proposed photodetection mechanisms such as plasmonic and other nanophotonic light sensing mechanisms,41-45 which commonly couple with other novel sensing nanomaterials or nanostructures to enhance device performances, this photodetection mechanism in the work alters the optical properties via directly controlling crystal structures of the sensing material itself. The proposed mechanism offers a new voltage control approach for photodetection and multi-functionalization of photodetectors.


11


Page 12 of 26

The electrochromic performances of the device were analyzed as presented in Figure 4. At the absence of any applied voltage, the initial color in the region between Au electrodes was the white color of Al2O3 substrate due to the high transparency of the WO3 film (Figure 4a). Once 4 or 5 V was applied to trigger the semiconductor-metal transition of WO3, the color changed to blue. When the voltage turned back to 0 V, the film was bleached back to its original transparency. The whole coloration and bleaching processes under positive and negative voltages were presented in Figure S8 and S9, respectively. The position and area of coloration region could vary in different coloration processes, which originated from the difficulty of meeting the high demand of uniform resistance distribution due to the film coating process on the interdigitated electrodes. This problem could be eliminated by improving the coating techniques and modifying the electrode structures. Therefore, as a verification of the proposed concept in this paper, the analyses of the electrochromic performances focused only on the coloration region. The contrasts at the regions of interest under different voltages and typical transition periods were depicted in Figure 4b and 4c, through the calculation of the Euclidean distances of the images in Figure S8 and S9 as introduced in the Supporting Information. The images on the right side of the curves, chopped from the photos shown in Figure S10, indicated the regions of interest with the small rectangles inside. Here, the maximum contrast, 100%, is defined as the Euclidean distance between the highest pixel value within the region of interest of a reference grayscale image (the image at 0 V in this case) and a chosen threshold (35 in this case, on a scale from 0 to 255). The curves demonstrated prominently increased contrasts from nearly 0% at ±1 V and ±2 V to over 90% at ±5 V. The very high color contrast at ±5 V validated the device’s application feasibility for electrochromic glasses and displays, whilst the contrast of nearly 0% at ±1 V and ±2 V indicated the stability of the device for the potential high-performance


12

Page 13 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


photodetection as discussed above. After the voltage was withdrawn, the contrast could be recovered to its initial status. The images in Figure S11 and S12 acquired based on calculation of the Euclidean distances illustrated the contrast changes, corresponding to the curves in Figure 4b and 4c, respectively. For visibility purposes, the images with the inverse color were shown. In addition, applying low voltage in the same or opposite direction could also postpone or accelerate the bleaching process to some extent.


13


Page 14 of 26

Figure 4. Electrochromic performances of the electrochromic photodetector. a) The steady coloration and bleaching photos of the device. b) The contrast analyses of the coloration and bleaching processes under positive voltages in the specific region as marked in the image. T1-


14

Page 15 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


T12 are the typical photos of the coloration process after the voltage was adjusted from 2 V to 4 V. B1-B6 are the typical photos of the bleaching process while the voltage was modulated to 0 V from 5 V. c) The contrast analyses of the coloration and bleaching processes under negative voltages in the specific region as marked in the image. T1-T9 are the typical photos of the coloration process after the voltage was adjusted from -2 V to -4 V. B1-B4 are the typical photos of the bleaching process while the voltage was modulated to 0 V from 5 V. d) The dynamic analyses of the electrochromic process. The sections in the images divided by dotted lines and indicated by orange rectangles with “+” and “-” signs denote positive and negative electrodes, respectively. For visibility purposes, the images with the inverse color were shown.

The operation mechanism was further explored based on the evidences observed from the electrochromic processes. The images extracted from Figure S8 after chopped for the region of interest were displayed in Figure 4d to represent the typical dynamic electrochromic process. The detailed image extraction technique about Figure 4d was given in the Section 3 of Supporting Information. As clearly indicated in the images, no apparent color change occurred at 1 and 2 V, which corresponds to the description of Figure 4b. To investigate the dynamic coloration process, the voltage was initially modulated to 4 V from 2 V in order to obtain the relatively slow transition process. At the beginning stage of the application of 4 V, the surroundings of negative electrodes were altered to the darker color, whereas these of positive electrodes kept almost unchanged, suggesting that the reduction reactions occurring in the WO3 film started from the negative electrodes. The reactions spread from the negative to positive electrodes, first forming grayish arc-shaped strips along the edges of negative electrodes. Then the grayish areas extended towards positive electrodes from the center of the strips and developed into round areas near


15


Page 16 of 26

positive electrodes. The areas further grew and darkened until reaching steady patterns. Those dark areas unable to reach the positive electrodes or further darken turned back to transparent. Increasing voltage from 4 V to 5 V only further broadened the coloration area. Upon the removal of applied voltage, the dark area promptly faded over the whole surface. Then the bleaching process continued at a relatively slow speed until the whole film turned back to transparent state. This could be explained by the participation of oxidant gas in the oxidation reaction of the active film, where the reaction on the surface proceeded rather easier and faster compared to the deeper region. As finally illustrated in Figure S13, the same phenomena were observed when the polarity of the applied voltage changed to negative. Therefore, considering the above analyses, the operation mechanism of electrochromism with the modulation of voltage can be resolved into the following two reversible steps. The first step was the water vapor splitting via the relatively high bias voltage: 2 H2O – 4 e- ⇌ 4 H+ + O2

(1)

The second step was the intercalation of protons into the active film: WO3 + x H+ + x e- ⇌ HxWO3 (0 < x < 1)

(2)

Hence, the total reaction included the participation of two gases from ambient air, water vapor and oxygen: 4 WO3 + 2x H2O ⇌ 4 HxWO3 + x O2 (0 < x < 1)

(3)

CONCLUSIONS

In summary, the new concept of electrochromic photodetector operating via voltage modulation aiming at fabrication of smarter glasses and nano reflective displays was proposed. The concept was demonstrated on an all-solid state, electrolyte-free, WO3-based device with a


16

Page 17 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


simple MSM configuration, which works through an electrolytic mechanism. The electrochromic photodetector switches between its photosensing and electrochromic functions via voltage modulation within 5 V, which is the result of semiconductor-metal transition. The transition mechanism was further analyzed to be the voltage-triggered reversible oxygen/water vapor adsorption/intercalation from ambient air. This work offers a fresh new pathway for further development of smarter electrochromic devices and points towards new possibilities in the design of multifunctional electronics.

EXPERIMENTAL SECTION Exfoliation of 2D WO3 nanosheets: 0.3 g commerical tungstic acid powder (H2WO4, ≥ 99%, ACROS Organics) was mixed into 25 mL solvent of 50:50 v/v EtOH/H2O. The mixtures were then transfered in a 30 ml glass vessel for microwave-assitant exfoliation. The microwave reactor (Discover SP, CEM Corporation) operated at 2.45 GHz and used a single-mode microwave setting. The vessel was placed in the reactor with high-speed strring under intial power of 120 W. The inner temperature was increased to 170 °C over 8 mins and kept constant for an additional 22 mins thereafter with the pressure in the vessel monitered to be ca.185 psi. After the process, the vessel was cooled to the room temperature and a homogeneous light yellow dispersion was formed with sediment remaining on the bottom. The sediment was discarded and the dispersion was kept for device fabrication. Device fabrication: The above-mentioned exfoliated dispersion was dried at 80 °C until the volume decreased to 5.6 mL. 10 μL of the concentrated dispersion was dropped on the alumina substrate with interdigitated electrode. The interdigitated electrode has 5 Au pairs, with 6 mm in


17


Page 18 of 26

length and 300 μm in both width and spacing. The substrate was heated at 120 °C for 30 mins on a hotplate and then increased to 380 °C for 4h. Characterization: The morphology and the elements of the sample were characterized using Field-Emission SEM (FE-SEM, JSM-7100F, Jeol) mounted with EDS. High-Resolution XRD (HR-XRD, SmartLab, Rigaku) were employed to analyze the crystal lattice structure of the sample. The UV-vis spectra were recorded on a UV-Vis-NIR Spectrophotometer (Cary 5000, Agilent Technologies). The chemical components in the sample were examined by a Thermo Scientific K-Alpha XPS. Device performance measurements: All the electric measurements including I-V characteristics, photoresponse and electrochromic response were performed using a Keithley 2614B sourcemeter. A λ=365 nm UV LED was used as the light source and modulated into ON/OFF interval of 80s/80s with an OMRON DH48S-S time relay for photoresponse tests. The incident powder on the surface of the device was measured to be 25 mW cm-2 by a Ranbond VLP-2000 power meter. The photos for the electrochomic phenomenon study were taken on an Olympus SZX16 stereo microscope mounted with an IMT IMTcamCCDPro2 camera.

ASSOCIATED CONTENT Supporting Information Detailed and additional results about material characterization, CV characteristics, photoresponse performances, and electrochromic performances of the WO3-based electrochromic photodetectors. AUTHOR INFORMATION Corresponding Author


18

Page 19 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


*Email:

[email protected]

*Email:

[email protected]

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT The work is supported by the Research and Development Program of Ghent University Global Campus, Korea. F.V. acknowledges the support from the Tomsk Polytechnic University Competitiveness Enhancement Program grant (VIU-316/2017). S.Z. acknowledges the support from the “100 Talents Program” of Shanxi Province, P.R. China. REFERENCES (1)

Mortimer, R. J. Electrochromic Materials. Chem. Soc. Rev. 1997, 26 (3), 147. https://doi.org/10.1039/cs9972600147.

(2)

Lee, S. H.; Deshpande, R.; Parilla, P. A.; Jones, K. M.; To, B.; Mahan, A. H.; Dillon, A. C. Crystalline WO3 nanoparticles for Highly Improved Electrochromic Applications. Adv. Mater. 2006, 18 (6), 763–766. https://doi.org/10.1002/adma.200501953.

(3)

Wen, R.-T.; Granqvist, C. G.; Niklasson, G. A. Eliminating Degradation and Uncovering Ion-Trapping Dynamics in Electrochromic WO3 Thin Films. Nat. Mater. 2015, 14 (10),


19


Page 20 of 26

996–1001. https://doi.org/10.1038/nmat4368. (4)

de Castro, I. A.; Datta, R. S.; Ou, J. Z.; Castellanos-Gomez, A.; Sriram, S.; Daeneke, T.; Kalantar-zadeh, K. Molybdenum Oxides – From Fundamentals to Functionality. Adv. Mater. 2017, 29 (40), 1701619. https://doi.org/10.1002/adma.201701619.

(5)

Kalantar-zadeh, K.; Ou, J. Z.; Daeneke, T.; Mitchell, A.; Sasaki, T.; Fuhrer, M. S. Two Dimensional and Layered Transition Metal Oxides. Appl. Mater. Today 2016, 5, 73–89. https://doi.org/10.1016/j.apmt.2016.09.012.

(6)

Xu, T.; Walter, E. C.; Agrawal, A.; Bohn, C.; Velmurugan, J.; Zhu, W.; Lezec, H. J.; Talin, A. A. High-Contrast and Fast Electrochromic Switching Enabled by Plasmonics. Nat. Commun. 2016, 7, 1–6. https://doi.org/10.1038/ncomms10479.

(7)

Jensen, J.; Hösel, M.; Kim, I.; Yu, J. S.; Jo, J.; Krebs, F. C. Fast Switching ITO Free Electrochromic

Devices.

Adv.

Funct.

Mater.

2014,

24

(9),

1228–1233.

https://doi.org/10.1002/adfm.201302320. (8)

Azam, A.; Kim, J.; Park, J.; Novak, T. G.; Tiwari, A. P.; Song, S. H.; Kim, B.; Jeon, S. Two-Dimensional WO3 Nanosheets Chemically Converted from Layered WS2 for HighPerformance

Electrochromic

Devices.

Nano

Lett.

2018,

18

(9),

5645–5651.

https://doi.org/10.1021/acs.nanolett.8b02150. (9)

Zhang, P.; Zhu, F.; Wang, F.; Wang, J.; Dong, R.; Zhuang, X.; Schmidt, O. G.; Feng, X. Stimulus-Responsive Micro-Supercapacitors with Ultrahigh Energy Density and Reversible

Electrochromic

Window.

Adv.

Mater.

2017,

29

(7),

1604491.

https://doi.org/10.1002/adma.201604491.


20

Page 21 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(10)

Patel, K. J.; Bhatt, G. G.; Ray, J. R.; Suryavanshi, P.; Panchal, C. J. All-Inorganic SolidState Electrochromic Devices: A Review. J. Solid State Electrochem. 2017, 21 (2), 337– 347. https://doi.org/10.1007/s10008-016-3408-z.

(11)

Wei, X.; Shen, P. K. Electrochromics of Single Crystalline WO3·H2O Nanorods. Electrochem.

Commun.

2006,

8

(2),

293–298.

https://doi.org/10.1016/j.elecom.2005.12.008. (12)

Avendaño, E.; Berggren, L.; Niklasson, G. A.; Granqvist, C. G.; Azens, A. Electrochromic Materials and Devices: Brief Survey and New Data on Optical Absorption in Tungsten Oxide and Nickel Oxide Films. Thin Solid Films 2006, 496 (1), 30–36. https://doi.org/10.1016/j.tsf.2005.08.183.

(13)

Yang, P.; Sun, P.; Mai, W. Electrochromic Energy Storage Devices. Mater. Today 2016, 19 (7), 394–402. https://doi.org/10.1016/j.mattod.2015.11.007.

(14)

Bange, K.; Gambke, T. Electrochromic Materials for Optical Switching Devices. Adv. Mater. 1990, 2 (1), 10–16. https://doi.org/10.1002/adma.19900020103.

(15)

Granqvist, C. G. Oxide Electrochromics: An Introduction to Devices and Materials. Sol. Energy Mater. Sol. Cells 2012, 99, 1–13. https://doi.org/10.1016/j.solmat.2011.08.021.

(16)

Thummavichai, K.; Xia, Y.; Zhu, Y. Recent Progress in Chromogenic Research of Tungsten Oxides towards Energy-Related Applications. Prog. Mater. Sci. 2017, 88, 281– 324. https://doi.org/10.1016/j.pmatsci.2017.04.003.

(17)

Kalantar-Zadeh, K.; Vijayaraghavan, A.; Ham, M. H.; Zheng, H.; Breedon, M.; Strano, M.


21


Page 22 of 26

S. Synthesis of Atomically Thin WO3 Sheets from Hydrated Tungsten Trioxide. Chem. Mater. 2010, 22 (19), 5660–5666. https://doi.org/10.1021/cm1019603. (18)

Cheng, Y.; Guan, G.; Zhang, Y.-W.; Han, M.-Y.; Liu, S.; Bai, S.; Tee, S. Y.; Xia, J. Electrostatic-Driven Exfoliation and Hybridization of 2D Nanomaterials. Adv. Mater. 2017, 29 (32), 1700326. https://doi.org/10.1002/adma.201700326.

(19)

Zhuiykov, S.; Kats, E.; Carey, B.; Balendhran, S. Proton Intercalated Two-Dimensional WO3 Nano-Flakes with Enhanced Charge-Carrier Mobility at Room Temperature. Nanoscale 2014, 6 (24), 15029–15036. https://doi.org/10.1039/c4nr05008h.

(20)

Cong, S.; Geng, F.; Zhao, Z. Tungsten Oxide Materials for Optoelectronic Applications. Adv. Mater. 2016, 28 (47), 10518–10528. https://doi.org/10.1002/adma.201601109.

(21)

Deb, S. K. Opportunities and Challenges in Science and Technology of WO3 for Electrochromic and Related Applications. Sol. Energy Mater. Sol. Cells 2008, 92 (2), 245–258. https://doi.org/10.1007/s10452-014-9495-y.

(22)

Barton, D. G.; Shtein, M.; Wilson, R. D.; Soled, S. L.; Iglesia, E. Structure and Electronic Properties of Solid Acids Based on Tungsten Oxide Nanostructures. J. Phys. Chem. B 2002, 103 (4), 630–640. https://doi.org/10.1021/jp983555d.

(23)

Saenger, M. F.; Höing, T.; Robertson, B. W.; Billa, R. B.; Hofmann, T.; Schubert, E.; Schubert, M. Polaron and Phonon Properties in Proton Intercalated Amorphous Tungsten Oxide Thin Films. Phys. Rev. B - Condens. Matter Mater. Phys. 2008, 78 (24), 245205. https://doi.org/10.1103/PhysRevB.78.245205.


22

Page 23 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(24)

Cook, B.; Liu, Q.; Butler, J.; Smith, K.; Shi, K.; Ewing, D.; Casper, M.; Stramel, A.; Elliot, A.; Wu, J. Heat-Assisted Inkjet Printing of Tungsten Oxide for High-Performance Ultraviolet Photodetectors. ACS Appl. Mater. Interfaces 2018, 10 (1), 873–879. https://doi.org/10.1021/acsami.7b15391.

(25)

Hai, Z.; Akbari, M. K.; Xue, C.; Xu, H.; Hyde, L.; Zhuiykov, S. Wafer-Scaled Monolayer WO3 Windows Ultra-Sensitive, Extremely-Fast and Stable UV-A Photodetection. Appl. Surf. Sci. 2017, 405, 169–177. https://doi.org/10.1016/j.apsusc.2017.02.031.

(26)

Moudgil, A.; Dhyani, V.; Das, S. High Speed Efficient Ultraviolet Photodetector Based on 500 nm Width Multiple WO3 Nanowires. Appl. Phys. Lett. 2018, 113 (10), 101101. https://doi.org/10.1063/1.5045249.

(27)

Liu, Q.; Cook, B.; Shi, K.; Butler, J.; Smith, K.; Gong, M.; Ewing, D.; Casper, M.; Stramel, A.; Elliot, A.; Wu, J. Interface Nanojunction Engineering of Electron-Depleted Tungsten Oxide Nanoparticles for High-Performance Ultraviolet Photodetection. ACS Appl. Nano Mater. 2018, 1 (1), 394–400. https://doi.org/10.1021/acsanm.7b00217.

(28)

Liu, J.; Zhong, M.; Li, J.; Pan, A.; Zhu, X. Few-Layer WO3 nanosheets for HighPerformance

UV-Photodetectors.

Mater.

Lett.

2015,

148,

184–187.

https://doi.org/10.1016/j.matlet.2015.02.088. (29)

Wang, Y.; Wang, X.; Xu, Y.; Chen, T.; Liu, M.; Niu, F.; Wei, S.; Liu, J. Simultaneous Synthesis of WO3−x Quantum Dots and Bundle-Like Nanowires Using a One-Pot Template-Free Solvothermal Strategy and Their Versatile Applications. Small 2017, 13 (13), 1603689. https://doi.org/10.1002/smll.201603689.


23


(30)

Page 24 of 26

Zheng, T.; Sang, W.; He, Z.; Wei, Q.; Chen, B.; Li, H.; Cao, C.; Huang, R.; Yan, X.; Pan, B.; Zhou, S.; Zeng, J. Conductive Tungsten Oxide Nanosheets for Highly Efficient Hydrogen

Evolution.

Nano

Lett.

2017,

17

(12),

7968–7973.

https://doi.org/10.1021/acs.nanolett.7b04430. (31)

Bai, S.; Zhang, K.; Wang, L.; Sun, J.; Luo, R.; Li, D.; Chen, A. Synthesis Mechanism and Gas-Sensing Application of Nanosheet-Assembled Tungsten Oxide Microspheres. J. Mater. Chem. A 2014, 2 (21), 7927–7934. https://doi.org/10.1039/c4ta00053f.

(32)

Hwang, E.; Seo, S.; Bak, S.; Lee, H.; Min, M.; Lee, H. An Electrolyte-Free Flexible Electrochromic Device Using Electrostatically Strong Graphene Quantum Dot-Viologen Nanocomposites.

Adv.

Mater.

2014,

26

(30),

5129–5136.

https://doi.org/10.1002/adma.201401201. (33)

Strukov, D. B.; Snider, G. S.; Stewart, D. R.; Williams, R. S. The Missing Memristor Found. Nature 2008, 453 (7191), 80–83. https://doi.org/10.1038/nature06932.

(34)

Ji, Y.; Yang, Y.; Lee, S. K.; Ruan, G.; Kim, T. W.; Fei, H.; Lee, S. H.; Kim, D. Y.; Yoon, J.; Tour, J. M. Flexible Nanoporous WO3-x Nonvolatile Memory Device. ACS Nano 2016, 10 (8), 7598–7603. https://doi.org/10.1021/acsnano.6b02711.

(35)

Liang, L.; Li, K.; Xiao, C.; Fan, S.; Liu, J.; Zhang, W.; Xu, W.; Tong, W.; Liao, J.; Zhou, Y.; Ye, B.; Xie, Y. Vacancy Associates-Rich Ultrathin Nanosheets for High Performance and Flexible Nonvolatile Memory Device. J. Am. Chem. Soc. 2015, 137 (8), 3102–3108. https://doi.org/10.1021/jacs.5b00021.

(36)

Qian, K.; Cai, G.; Nguyen, V. C.; Chen, T.; Lee, P. S. Direct Observation of Conducting


24

Page 25 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Filaments in Tungsten Oxide Based Transparent Resistive Switching Memory. ACS Appl. Mater. Interfaces 2016, 8 (41), 27885–27891. https://doi.org/10.1021/acsami.6b08154. (37)

Wu, W. T.; Wu, J. J.; Chen, J. S. Resistive Switching Behavior and Multiple Transmittance States in Solution-Processed Tungsten Oxide. ACS Appl. Mater. Interfaces 2011, 3 (7), 2616–2621. https://doi.org/10.1021/am200430y.

(38)

Mitchell, J. B.; Lo, W. C.; Genc, A.; Lebeau, J.; Augustyn, V. Transition from Battery to Pseudocapacitor Behavior via Structural Water in Tungsten Oxide. Chem. Mater. 2017, 29 (9), 3928–3937. https://doi.org/10.1021/acs.chemmater.6b05485.

(39)

Liang, L.; Zhang, J.; Zhou, Y.; Xie, J.; Zhang, X.; Guan, M.; Pan, B.; Xie, Y. HighPerformance Flexible Electrochromic Device Based on Facile Semiconductor-To-Metal Transition Realized by WO3·2H2O Ultrathin Nanosheets. Sci. Rep. 2013, 3, 1936. https://doi.org/10.1038/srep01936.

(40)

Wang, F.; Di Valentin, C.; Pacchioni, G. Semiconductor-to-Metal Transition in WO3-x: Nature of the Oxygen Vacancy. Phys. Rev. B - Condens. Matter Mater. Phys. 2011, 84 (7), 073103. https://doi.org/10.1103/PhysRevB.84.073103.

(41)

Ahmadivand, A.; Sinha, R.; Vabbina, P. K.; Karabiyik, M.; Kaya, S.; Pala, N. Hot Electron Generation by Aluminum Oligomers in Plasmonic Ultraviolet Photodetectors. Opt. Express 2016, 24 (12), 13665. https://doi.org/10.1364/OE.24.013665.

(42)

De Sanctis, A.; Jones, G. F.; Wehenkel, D. J.; Bezares, F.; Koppens, F. H. L.; Craciun, M. F.; Russo, S. Extraordinary Linear Dynamic Range in Laser-Defined Functionalized Graphene

Photodetectors.

Sci.

Adv.

2017,

3

(5),

e1602617.


25


Page 26 of 26

https://doi.org/10.1126/sciadv.1602617. (43)

Tanzid, M.; Ahmadivand, A.; Zhang, R.; Cerjan, B.; Sobhani, A.; Yazdi, S.; Nordlander, P.; Halas, N. J. Combining Plasmonic Hot Carrier Generation with Free Carrier Absorption for High-Performance Near-Infrared Silicon-Based Photodetection. ACS Photonics 2018, 5 (9), 3472–3477. https://doi.org/10.1021/acsphotonics.8b00623.

(44)

Paria, D.; Jeong, H.-H.; Vadakkumbatt, V.; Deshpande, P.; Fischer, P.; Ghosh, A.; Ghosh, A. Graphene–Silver Hybrid Devices for Sensitive Photodetection in the Ultraviolet. Nanoscale 2018, 10 (16), 7685–7693. https://doi.org/10.1039/C7NR09061G.

(45)

Li, D.; Zhou, D.; Xu, W.; Chen, X.; Pan, G.; Zhou, X.; Ding, N.; Song, H. Plasmonic Photonic Crystals Induced Two-Order Fluorescence Enhancement of Blue Perovskite Nanocrystals Photodetectors.

and

Its

Application

Adv.

Funct.

for

High-Performance

Mater.

2018,

28

Flexible (41),

Ultraviolet 1804429.

https://doi.org/10.1002/adfm.201804429.

TOC


26

Electrochromic Photodetectors: Toward Smarter Glasses and Nano

Recommend Documents