Scalable-Production, Self-Powered TiO2 NanowellâOrganic Hybrid

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Scalable Production, Self-Powered TiO Nanowells/Organic Hybrids UV Photodetectors with Tunable Performances Lingxia Zheng, Pingping Yu, Kai Hu, Feng Teng, Hongyu Chen, and Xiaosheng Fang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b11012 • Publication Date (Web): 18 Nov 2016 Downloaded from http://pubs.acs.org on November 19, 2016

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ACS Applied Materials & Interfaces

Scalable Production, Self-Powered TiO2 Nanowells/Organic Hybrids UV Photodetectors with Tunable Performances Lingxia Zheng, Pingping Yu, Kai Hu, Feng Teng, Hongyu Chen, and Xiaosheng Fang* Department of Materials Science, Fudan University, Shanghai 200433, P. R. China E-mail: [email protected] (X.S. Fang) KEYWORDS. Self-powered photodetectors, polyaniline, TiO2, inorganic/organic, fast repsonse

ACS Paragon Plus Environment

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ABSTRACT. Hybrid inorganic/organic photoelectric devices draw considerable attention because of their unique features by combining the tunable functionality of organic molecules and the superior intrinsic carrier mobilities of inorganic semiconductors. An ordered thin-layer of TiO2 nanowells are formed in situ with shallowed nanoconcave patterns without cracking with scalable production by a facile and economic strategy, and used as building blocks to construct hybrid UV photodetectors (PDs). Organic conducting polymer (polyaniline (PANI) with various morphologies) has been exploited as p-type materials, enabling tunable photodetection performances at zero bias. The thin layer of n-type TiO2 nanowells is favorable for electron transport and light absorption with respect to their conventional nanotubular counterparts. While PANI acts as a hopping-state/bridge to largely enhance the transition probability of the valence electrons in TiO2 to its conduction band, resulting in an increase in photocurrent in a selfpowered mode. In particular, the lowest polyaniline loading sample (TP1) exhibits the highest responsivity (3.6 mA.W-1), largest on/off switching ratio (~103), excellent wavelengthselectivity, fast response speed (3.8/30.7 ms) and good stability under 320 nm light illumination (0.56 mW.cm-2) without an external energy supply. This work might be of great value in developing tunable UV photoresponse materials with respect to low-cost and large area for future energy-efficient optoelectronic devices.


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1. Introduction To meet the great demand in a large variety of applications including optical communications,1 biological/chemical sensing,2-4 imaging, and optoelectronic circuits,5,

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self-powered UV

photodetectors (PDs), without consuming an external energy supply, are attracting numerous attentions nowadays. Great efforts in fabricating self-powered devices have been demonstrated the potential to build independent, sustainable and zero-maintenance nanosystems, through the construction of p-n junctions, Schottky junctions and heterojunctions due to the efficient separation ability of photogenerated electron-hole pairs by the photovoltaic effect.5,

7-13

Unfortunately, it is still costly and sophisticated to fabricate highly crystalline junctions and thus not suitable for practical large-scale devices. Therefore, it would be greatly advantageous to explore novel junction configurations of self-powered PDs via a simple and low-cost strategy with high detecting performance.14 Junctions between p-type and n-type semiconductor materials have built-in potential difference acting like a driving force to direct the movement of photogenerated electrons and holes. To date, various inorganic semiconductor nanomaterials, such as TiO2,15 ZnO,16 SnO2,17 Nb2O518 and GaN10, have been extensively studied as n-type semiconductors during the last decade in low-cost heterojunctions for UV and visible photodetection. In particular, TiO2 has been extensively studied as an important n-type semiconductor in visible-blind UV light sensors owing to its distinct UV absorption characteristics with a wide bandgap.15, 19, 20 Anatase TiO2 films are proven to exhibit wider bandgap (~3.2 eV), larger electron mobility, and lower defect concentration at the film surface, promising for UV detectors.21, 22 Among numerous synthetic strategies, anodization represents a most elegant and versatile solution-based approach to grow one-dimensional TiO2 nanotubes (NTs) in an entirely self-organization manner with large


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scale.23,

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Owing to their good biocompatibility, high stability, abundant availability24-26 and

superior performances15,

27-29

, e.g., excellent light-trapping, large specific surface area, well-

defined charge carriers transport pathway and so on, anatase TiO2 NTs attracted considerable interest in the opto/electronic devices. For example, with a large surface area, TiO2 NTs-based PDs were found to demonstrate a high responsivity of 13 A.W-1 at 2.5 V bias.20 As p-type oxide semiconductor is rare, full oxide p-n junction photodetector is hard to achieve.30,31 One promising solution is to adopt organic semiconducting polymers with p-type conductivity to construct hybrid inorganic/organic heterojunction devices. The emergence of organic conducting polymers for photovoltaic devices has opened a new area in designing new materials for energy conversion owing to their unique properties that conventional inorganic materials do not possess, such as ease of processing, large device area, low cost and high flexibility.4 In particular, polyaniline (PANI) is a well-studied p-type conducting polymer, desirable for hole collection and transport layer in p-n junction configuration. For instance, Wu J. et al. accomplished a highly efficient p-n heterojunction diode comprising of p-type PANI microrods and n-type ZnO nanowires by a controlled electrochemical deposition method.32 Deng Y. et al. demonstrated a sandwich-structured UV photodetector based on one layer of PANI nanowires and two layers of n-type ZnO nanorods with high photocurrent (~1.4×105 A) and photosensitivity (>105) at zero bias.33 Yang S. et al. reported that the PANI functionalized MnO2 nanocomposite based photodetector exhibited reversible and highly efficient photoresponse.34 These studies suggested that the p-type conducting PANI can functions synergistically in the detection of optical signals in the inorganic/organic heterojunction devices. Herein, we report the development and application of novel heterojunctions consisting of ntype TiO2 nanowells and p-type PANI with tunable morphologies in PD devices. An array of


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ordered TiO2 nanowells is used as the pathway for electron transport and light scattering structure. While p-type PANI nanostructures act as the hole transport layer. The results demonstrate that the incorporation of PANI into TiO2 system successfully realizes highly efficient self-powered PDs with high on/off switching ratio, excellent wavelength dependance, fast photoresponse speed and good stability. Moreover, the photocurrent/responsivity greatly decreases with the increasing amount of PANI owing to the dramatically reduced effective junction area under irradiation between TiO2 and PANI together with the decreased active sites of TiO2. The innovative strategy of constructing TiO2-based p-n junction configuration with scalable production into optoelectronic devices might envisage strong impact in future energysufficient optoelectronic applications. 2. Methods Preparation of anatase TiO2 nanowells: The Ti foils (99.7% purity, 0. 25 mm thick, Sigma Aldrich) were ultrasonically cleaned in acetone, ethanol and deionized water successively, and then dried in a nitrogen stream. The preparation of TiO2 nanotubes was carried out following the well-established anodization process35 in a two-electrode electrochemical cell with a Pt gauze as the counter electrode. The Ti working anode was pressed together with an Al foil against an Oring, defining a working area of ~1.77 cm2 (diameter of 1.5 cm). The Ti foils were anodized at 45 V for 7.5 h in the electrolyte containing 0.35 wt% NH4F (85% Lactic Acid), and 10 vol% DMSO (dimethyl sulphoxide, >99%, Sinopharm Chemical Reagent Co., Ltd, Shanghai, China) with a Keithley 2450 Sourcemeter. To obtain the anatase TiO2 nanowells, the as-anodized film was ultrasonicated in water to remove the nanotube layer and surface debris, leaving an ordered concave pattern, namely nanowells on the substrate. To increase the crystalline of TiO2, the asexposed nanowells substate was thermally treated at 450 oC in air for 2 h at a rate of 3 ºC·min−1.


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Synthesis of TiO2/PANI hybrids:The detailed fabrication process is illustrated in Scheme 1. The polymerization was carried out in an ice-water bath at a temperature of 10 °C and -5 °C, respectively, to yield TiO2/PANI hybrids with different PANI loading (denoted as TP1, TP2, respectively). At 10 °C, anatase TiO2 nanowells substrate was immersed into 1 M H2SO4 (20 mL) aqueous solution containing aniline monomer (ANI, 27.39 µL), and stirred for 10 min to ensure complete dispersion of the ANI onto the TiO2 nanowells. Then, another 20 mL of 1 M H2SO4 aqueous solution containing ammonium persulfate (APS, 68.48 mg) was rapidly added and the mixture was stirred for 30 s. The molar ratio of ANI to APS was 1:1. After reacting for 24 h, the TiO2/PANI hybrid (TP1) was taken out and washed with deionized water for several times. Sample TP2 was fabricated under similar conditions but at a temperature of -5 °C. To study the extreme case (the most loading amount of PANI), sample TP3 was prepared by performing in situ polymerization at -5 °C for twice. i.e., We used TP2 as the substrate and immersed it in ANI monomer acid solution, and then APS acid solution was added to react for another 24 h. Finally, the substrate was washed with distilled water and ethanol, respectively, and dried at 60 ºC for 6 h to produce TiO2/PANI hybrids (TP3). Charaterizations: Sample morphologies were characterized using field-emission scanning electron microscopy (FESEM, Zeiss Sigma). X-ray diffraction (XRD) patterns were collected on a Bruker D8-A25 diffractometer using Cu Kα radiation (λ = 1.5405 Å). Raman spectroscopy (Horiba Jobin Yvon XploRA, France) with a 532 nm Nd:YAG laser was employed to verify chemical bonding characteristics. The optical properties were investigated by optical diffuse absorption spectra using a UV-vis spectrophotometer (Hitachi U-3900H) with an integrating sphere attachment.


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Photoelectric measurements: To construct a detector device, small silver pastes with area (≈0.005 cm2) were doctoral-bladed onto the sample as electrodes. The irradiated sample area is estimated to be ~0.8 mm2. The photoelectric performance was analysed with an Xe lamp, monochromator, a program-controlled semiconductor characterization system (Keithley 4200, USA). The light intensity was measured with a NOVA II power meter (OPHIR photonics). The temporal response of the photodetector was measured by a Nd: YAG 355 nm pulsed laser (Continuum Electro-Optics, MINILITE II) with pulse width of 3-5 ns and an oscilloscope (Tektronix DPO 5140B). All the measurements were performed at room temperature under ambient conditions. 3. Results and Discussion

Scheme 1. Schematic illustration of the fabrication process. Figure 1 reveals the typical scanning electron microscopy (SEM) images of different TiO2based nanostructures. Self-ordered one-dimensional TiO2 NT arrays are obtained as shown in Figure 1a with outer tube diameters ranging from 160 nm to 250 nm. The inset indicates that all the nanotubes are vertically aligned on the Ti substrate with a film length of ~2.5 µm. Figure 1b shows that the TiO2 nanowells exhibit two-dimensional periodicity in a large scale without


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cracking, which are formed in situ with shallowed nanoconcave patterns in the Ti substrate. The average diameters are found to be ~200 nm, same as the top tube’s diameters. The thin layer of TiO2 nanowells (~150 nm-thick, Figure S1a) ensures a shorter diffusion path in contrast to TiO2 NTs counterparts,36 but maintaining the self-ordered features with large area. Moreover, it is worth noticing that the scale of the nanoconcaved structural basis can be readily adjusted by the size of Ti starting material for anodization, which guarantees its feasibility for scale-up in large area PD devices via a facile and low-cost route. Figure 1c,d present the structural morphology of sample TP1 with the lowest loading of PANI. Small PANI nanofibers with diameters ranging from 30 to 65 nm are randomly grown on top surface of TiO2 nanowells. Note that most part of TiO2 layer is exposed to the environment, which is favorable for UV light harvest by TiO2.

Figure 1. Plane-view SEM images of (a) TiO2 NT arrays, (b) TiO2 nanowells and (c,d) TiO2/PANI hybrids (TP1). Inset in (a) shows the cross-section of TiO2 NTs. Insets in (b-d) are the corresponding magnified images.


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Figure 2a shows that a continous film of PANI forms ontop with the same porous morphology as the beneath TiO2 nanowells for sample TP2. i.e., the PANI film mostly covers the edges of each TiO2 nanowell, and leaving the bottom of the nanowell exposed to the environment, favorable for light absorption by TiO2 nanowells. The thickness of thin layer PANI is approximately 25 nm (inset in Figure S1b). At the extreme case for sample TP3, uniform small PANI nanoclusters film are found to fully cover the TiO2 underlayer. The layer thickness of PANI in TP3 is approximately 350 nm as revealed by the cross-sectional SEM image in Figure S1c,d. Therefore, sample TP1 has the largest part of TiO2 layer exposed to the environment with respect to samples TP2 and TP3, which takes most advantages of UV light absorption by TiO2, promising for the photoresponse properties.

Figure 2. SEM images of sample TP2 (a,b) and TP3 (c,d) at different magnifications. X-ray diffraction (XRD) patterns were studied to examine the structural features of TiO2 nanowells and three TiO2/PANI hybrids (Figure 3a). A major peak centred at 25.3º, assigning to


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(101) facet of anatase TiO2 (JCPDS card no. 21-1272) can be observed for TiO2 and TiO2/PANI hybrids. Other peaks agreed well with Ti metal (JCPDS no. 44-1294) are so strong and sharp that the signals for PANI species (Figure S2) in the TiO2/PANI hybrids are undetectable. Raman spectroscopy was performed to further examine the existense of PANI in the three hybrids. As shown in Figure 3b, all the three samples TP1-TP3 exhibit the same pattern in the 1000-2000 cm1

region while no obvious peaks for TiO2 nanowells can be observed, revealing the successful

incorpration of PANI species into the TiO2/PANI hybrids. The characteristic peaks loacted at 1164, 1236, 1337, 1507 and 1594 cm-1 for samples TP1-TP3 can be attributed to C-H bending of the quinoid ring, C-N vibration of the benzene diamine units, C=N vibration of the quinoid nanoprotonated diimine units, C=C vibration of the quinoid rings and C-C strentching of the benzenoid ring, respectively, owing to the presence of PANI.37 The inset in Figure 3b shows the Raman spectrum for TiO2 nanowells in the 100-1000 cm-1 region, and the three characteristic peaks, ascribing to O-Ti-O symmetric deformation vibration and Ti-O stretching viration, further confirmed the anatase phase of TiO2, consistent with the XRD data in Figure 3a.38, 39


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Figure 3. (a) XRD patterns (b) Raman spectra of pristine TiO2 nanowells, and samples TP1-TP3. The inset in (b) shows the Raman spectrum of TiO2 nanowells in the 100-1000 cm-1 region. The optical properties are determined by UV-vis diffuse absorption spectra as shown in Figure 4. Interestingly, all the samples exhibit strong light absorption in the visible range (400-700) due to their selective light absorption of the photonic bandgaps (periodicity of nanoconcaved patterns in the Ti surface), leading to colorful sample appearances, and could be possibly useful in preparing photonic crystal materials.40 Samples TP1-TP3 exhibit distinctly different colors: purple, blue and dark green, respectively, with increasing amount of PANI. For TP1, no obvious color change can be readily observed by naked eyes and no additional peaks assigning to PANI is detected. Therefore it has the same absorption characteristics as those of bare TiO2 nanowells


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but with dramatically increasing light absorption intensity within UV range (200-400 nm), which suggests enhanced generation of electron-hole pairs after the introduction of PANI into TiO2. The absorption intensities increase slightly for TP2 when increasing amount of PANI, comparing to that of TP1. A new peak centred at 215 nm emerges which can be assigned to the π–π* transition of the bezenoid rings of PANI.41 Interestingly, the spectrum pattern of sample TP3 is different from those of TP1 and TP2, while similar to that of pure PANI sample as displayed in the inset of Figure 4. The absorption peaks located at 223, 354 and 444 nm is attributed to the π– π* transition, the polaron band to π* transition, and π to localized polaron band of PANI, respectively. These bands indicate that the PANI is in their conducting form (i.e., the emeraldine salt form of PANI, consistent with the dark green appearance of TP3).34, 42 However, the high absorption intensities of both TP2 and TP3 are induced by the upper thicker layer of PANI instead of TiO2, as most portion of the light is absorbed by the continuous PANI film ontop and this non-transparent layer (~350 nm-thick) block the light to some extent, thus only very small portion of light can reach the beneath TiO2 (SEM images in Figure 2).


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Figure 4. UV-vis diffuse absorption spectra of TiO2 nanowells, and TiO2/PANI hybrids TP1TP3 and their corresponding optical graphs. The inset shows the spectrum of pure PANI sample. The photoelectrical and UV detection properties as photodetector devices were carefully examined under ambient condition and monochromatic illumination based on TiO2/PANI hybrids. To construct the device, small silver pads were doctor-bladed onto the sample and directly used as the electrodes as illustrated in Figure 5a. Figure 5b reveals the current-voltage (I-V) curves of device TP1 under dark and different wavelengths of light source at 500, 400, 350 and 320 nm with the applied bias from -1 V to 1 V. The dramatic photocurrent increase under 350 nm and 320 nm light illumination can be ascribed to the enhanced numbers of photoexccited electron-hole pairs when the photon’s energy is larger than the bandgap of TiO2 and TP1.38, 43 The non-lineararity of the I-V curves feature an excellent photovoltaic property with a shortcircuit current of ~34 nA and an open circuit voltage Voc =0.15 V. Thus, the hybrid device TP1 can work in a self-powered mode without any external power supply. As two types of junctions (Schottky junction and p-n junction) might be existed in this hybrid device, more information needs to obtain to understand the origin of the self-powered response. PDs based on both pure TiO2 nanowells and pure PANI sample were constructed, and the I-V curves were measured under dark condition and upon 350 nm light illumination. As shown in Figure S3a, the symmetric I-V curves for pristine TiO2 nanowells indicate that the Schottky junction from Ag/TiO2 is unable to induce self-powered behavior.36 While the linear I-V curves for pure PANI device under dark indicates good ohmic contacts at Ag/PANI and no photoresponse can be detected upon 350 nm light illumination (Figure S3b). Thus, it is safe to conclude that the builtin potential (Voc) in the hybrid device TP1 are the main result of p-n junction at PANI and TiO2 interface, which acts as a driving force to separate the photogenerated electron-hole pairs and


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produce large photocurrent, leading to self-powered response. For the other two types of hybrid PDs based on TP2 and TP3, similar self-powered characteristics are observed as revealed by the I-V curves in Figure 5c and 5d. Both exhibit similarly large current increase under 350 and 320 nm light irradiation, and the asymmetric curves at the negative and positive biases also suggest that the as-fabricated inorganic/organic heterojunction PDs should also be p-n junction contacts. Interestingly, much smaller values of Voc under 320 nm light illumination are found of device TP2 (Voc=0.01 V, inset in Figure 5c) and device TP3 (Voc=0.0075 V Figure 5d), suggesting a relatively weaker self-powered behaviors with inceasing loading amount of PANI. To further explore the signal-to-noise of device TP1, the linear dynamic range (LDR, typically quoted in dB) is a figure-of-merit for a PD and can be expressed as the equation:44 LDR (dB) = 20 log (Iph /Id)

(1)

Considering that the dark current should be zero for an ideal PD, a very small bias of 0.05 V is adopted to evaluate the signal-to-noise. The LDR is calculated to be ~101 dB at 320 nm, much larger than those of InGaAs PDs (66 dB),45 which indicates a relatively large ratio of photocurrent to dark current and a high signal-to-noise ratio.


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Figure 5. (a) Schematic diagram of PD devices based on TiO2/PANI hybrids. (b-d) Typical I-V curves of device TP1, TP2 and TP3, respectively, under different wavelengths light illumination of 500, 400, 350 and 320 nm, and under dark condition. The inset in (c) indicates the enlarged IV curves from -0.05 V and 0.05 V. The spectral responsivity (Rλ) is a critical parameter to determine the sensitivity of optoelectronic devices, which is defined as the number of carriers circularing through a photodetector per absorbed photon.18,

46

A larger Rλ represents a higher sensitivity and is

expressed as the following equation: Rλ= (Iph-Id)/(PS)

(2)

where Iph is the photocurrent, Id is the dark current, λ is the excition wavelength, P and S are the light power density and the effective irradiated area, respectively. The calculated Rλ is as high as 3.6 mA.W-1 under light illumination of 320 nm (light intensity of 0.87 mW.cm-2) at 0 V bias as shown in Figure 6a. The self-powered device TP1 is intrinsically “visible-light-blind” with a cut-off wavelength of about 400 nm. Note that the sharp cut-off edge and the relatively high UV-


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visible rejection ratio (R290nm/R400nm=~34) at zero bias indicate that our device is a highperformance intrinsic visible-blind self-powered UV photodetector. Accordingly, the spectral responsivity spectra for the other two devices are revealed in Figure 6b and 6c. Devices TP2 and TP3 exhibit the same spectral responsivity profiles with a maxima values of 785 and 70 µA.W-1 at zero bias, respectively. Both show a cut-off wavelength of ~400 nm and the highest responsitivity located at 290 nm at 0 V bias, indicating good wavelength selectivity. For comparison, the responsivities under 320 nm light illumination (R320 nm) for the threee devices are listed in Table 1 and they follow the order: TP1>TP2>TP3. Moreover, by assuming the shot noise from the dark current is the major contributor, the detectivity (D*) can be calculated as: 47-50 D*=Rλ/(2eIdS)1/2

(3)

which reflects the ability to detect weak signal from the noise environment. Owing to the suppressed dark current and enhanced responsivity, the D* is as high as 3.9×1011 Jones at the wavelength of 320 nm under a small bias of 0.05 V.

Figure 6. (a-c) Spectral responsivity spectra for devices TP1-TP3 under zero bias, repectively. Besides sensitity and selectivity, stability is also a very significant factor for PD devices. The time-dependent photocurrent curves (Figure 7a-c) suggests good stability and reversibility without notable photocurrent-decay for all the three devices TP1-TP3. For device TP1 in Figure 7a, when the condition changes from dark to light, the current increases quickly to a stable value


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around 32 nA, and decays dramatically to the original value when the light switched off. The photo-to-dark current ratio ((Iph-Id)/Id) is estimated to be 1.3×103. The photocurrent values decrease greatly for devices TP2 and TP3 (Table 1) due to the weaker self-powered response, consistent with the I-V results in Figure 5. The response speed is a key parameter to determine the properties of a PD to react to a fast-changing optical signal. Obviously, the rise time τr and decay time τd of all the three devices from the I-t curves are less than 0.3 s (limitation of the measurement system) as no data points can be collected upon light switching. Thus, a 355 nm pulsed Nd:YAG laser as the optical source with an oscilloscope was used to measure the timeresolved response at 0 V51 and the results are shown in Figure 7d-f and Table 1. The time interval between two collected data points was 50 µs. The rise time (defined as the time required for the peak photocurrent to increase from 10% to 90%) and decay time (peak photocurrent to drop from 90% to 10%) are estimated to be 3.8 and 30.7 ms for device TP1, respectively, indicating ultrafast response speed with high photosensitivity as a self-powered device. Similarly, both the other devices exhibit a fast response speed with times in milliseconds (4.5/33.6 ms for device TP2, Figure 7e; 1.2/22.8 ms for device TP3, Figure 7f; Table 1). The high sensitivity and good stability as well as fast response speed of the self-powered hybrid inorganic/organic devices are promising for large-area photodetector applications. Table 1 is a comparison among various hybrid inorganic/organic PDs related to this work. Although some devices showed higher photocurrent/responsivity, they either required higher appied voltage or exhibited slower photoresponse speed. While our devices have the advantages of ease of fabrication and zero-bias operation.


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Figure 7. (a-c) The I-t curves at 0 V bias under 320 nm light illumination of devices TP1-TP3, respectively, and (d-f) their corresponding time-resolved responses measured by a 355 nm laser . In addition, the photosensitivity of device TP1 to 320 nm UV light illumination was further examined using a range of irradiances of 0.1-0.56 mW.cm-2 light intensities (Figure 8a). Note that a steadily increasing photocurrent response in relation to the light intensity, achieving a photocurrent of 40 nA at 0.56 mW.cm-2, consistent with the fact that the charge carrier photogeneration efficiency is proportional to the absorbed photon flux. The nonlinear relationship for the variation of photocurrent against light intensity upon 320 nm light illumination (inset in Figure 8a) suggests a complex process of electron–hole generation, recombination, and trapping within the self-powerd device.15, 18, 52, 53


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Table 1. Comparison of the characteristic parameters for TiO2/PANI hybrid photodetectors and other hybrid inorganic/organic photodetectors related to this work. Photodetector

Light of detection

Bias

Photocurre nt

Responsivi ty

Rise timea)

Decay time b)

TiO2/spiroMeOTAD

410 nm; 75 μW cm-2

0V

~0.1 μA

0.01 A W-1

0.12s

0.06 s

30

TiO2/PANI/TiO2

365 nm; 8 W

0V

~0.8 μA

—

1s

2s

54

ZnO/PANI

350 nm

5V

0.4×10-6 A

—

47 s

58 s

55

ZnO/PANI/ZnO

365 nm; 8W

0V

~1.4×10-5 A

—

—

—

33

TiO2/mCP

335 nm

-10 V

—

240 A W-1

21 ms

23 ms

56

P3HT:CdSe

140 mW cm-2

3V

320 nA

—

TP3. It can be explained by the decreasing effective junction area under irradiation between PANI and TiO2, which largely reduces the generation of electron-hole pairs, verified by the SEM images of TP1-TP3 (Figure 1 and 2). The effective junction area exposed to UV light is the largest for TP1, leading to the highest Voc and greatest self-powered response. On the other hand, as no photoresponse can be detected upon 350 nm light illumination of pure PANI device (Figure S3b), TiO2 plays a more vital role in the good UV light sensing performance. However, the thicker PANI films of both TP2 and TP3 samples block the light irradiation to some extent, and thus less effective sites of underneath TiO2 layer can be reach by UV light.


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4. Conclusion In summary, three types of inorganic/organic hybrids PDs based on an array of ordered TiO2 nanowells and p-type conducting PANI (TP1-TP3) were successfully prepared and realized as self-powered devices with enhanced photoresponse including high responsivity, excellent wavelength selectivity, fast speed and good stability. The thin layer of n-type TiO2 nanowells is used as the pathway for electron transport and light scattering. While PANI acts as a hoppingstate/bridge to largely enhance the transition probability of the valence electrons in TiO2 to its conduction band, resulting in an increase in photocurrent in a self-powered mode. Interestingly, the performances can be easily tuned by adjusting the loading amount of PANI in the nanohybrids. It is found that the photocurrent/responsivity greatly decreases with the increasing PANI amount due to the reduced effective junction area under irradiation between TiO2 and PANI and the decreased active sites of TiO2. The fast transient response (milliseconds) for the three devices is highly desirable for practical applications in high-frequency/high-speed devices. This work presents us an economic strategy to develop future tunable inorganic/organic heterojunction devices in a self-powered mode. ASSOCIATED CONTENT Supporting Information. SEM images, XRD patterns and I-V curves. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author E-mail: [email protected] (X.S. Fang) Author Contributions


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The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ACKNOWLEDGMENT The work was supported by the National Natural Science Foundation of China (Grant Nos. 51471051 and 61505033), Science and Technology Commission of Shanghai Municipality (15520720700), Shanghai Shu Guang Project (12SG01), the Programs for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning, China Postdoctoral Science Foundation (2014M560294). Part of the experimental work have been carried out in Fudan Nanofabrication Laboratory. REFERENCES (1)

Elgala, H., Mesleh, R., Haas, H., Indoor Optical Wireless Communication: Potential and

State-of-the-Art. IEEE Commun. Mag. 2011, 49, 56-62. (2)

Tian, B., Lieber, C. M., Design, Synthesis, and Characterization of Novel Nanowire

Structures for Photovoltaics and Intracellular Probes. Pure Appl. Chem. 2011, 83, 2153-2169. (3)

Wang, J.; Yan, C.; Kang, W.; Lee, P. S., High-Efficiency Transfer of Percolating

Nanowire Film for Stretchable and Transparent Photodetectors, ACS Nano 2014, 8, 6038-6046. (4)

Wang, X., Song, W., Liu, B., Chen, G., Chen, D., Zhou, C., Shen, G., High-Performance

Organic-Inorganic Hybrid Photodetectors Based on P3HT:CdSe Nanowire Heterojunctions on Rigid and Flexible Substrates.Adv. Funct. Mater. 2013, 23, 1202-1209. (5)

Bie, Y. Q., Liao, Z. M., Zhang, H. Z., Li, G. R., Ye, Y., Zhou, Y. B., Xu, J., Qin, Z. X.,

Dai, L., Yu, D. P., Self-Powered, Ultrafast, Visible-Blind UV Detection and Optical Logical Operation Based on ZnO/GaN Nanoscale P-N Junctions. Adv. Mater. 2011, 23, 649-653.


22

Page 23 of 30

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


(6)

Chen, H. Y., Liu, H., Zhang, Z. M., Hu, K., Fang, X. S., Nanostructured Photodetectors:

From Ultraviolet to Terahertz. Adv. Mater. 2016, 28, 403-433. (7)

Fang, X. S., Hu, L. F.; Huo, K. F.; Gao, B.; Zhao, L. J.; Liao, M. Y.; Chu, P. K.; Bando,

Y., Golberg, D., New Ultraviolet Photodetector based on Individual Nb2O5 Nanobelts, Adv. Funct. Mater. 2011, 21, 3907-3915. (8)

Chen, H. Y., Liu, K. W., Hu, L. F., Al-Ghamdi, A. A., Fang, X. S., New Concept

Ultraviolet Photodetectors. Mater. Today 2015, 18, 493-502. (9)

Huang, S., Wu, H., Matsubara, K., Cheng, J., Pan, W., Facile Assembly of n-SnO2

Nanobelts-p-NiO Heterojunctions with Enhanced Ultraviolet Photoresponse. Chem. Commun. 2014, 50, 2847-2850. (10)

Bilousov, O. V., Carvajal, J. J., Geaney, H., Zubialevich, V. Z., Parbrook, P. J., Martinez,

O., Jimenez, J., Diaz, F., Aguilo, M., O'Dwyer, C., Fully Porous GaN P-N Junction Diodes Fabricated by Chemical Vapor Deposition. ACS Appl. Mater. Interfaces 2014, 6, 17954-17964. (11)

Dai, W., Pan, X., Chen, S., Chen, C., Wen, Z., Zhang, H., Ye, Z., Honeycomb-Like

NiO/ZnO Heterostructured Nanorods: Photochemical Synthesis, Characterization, and Enhanced UV Detection Performance. J. Mater. Chem. C 2014, 2, 4606-4614. (12)

Choi, M. S., Qu, D., Lee, D., Liu, X., Watanabe, K. T., Takashi , Yoo, W. J., Lateral MoS2

P–N Junction Formed by Chemical Doping for Use in High-Performance Optoelectronics. ACS Nano 2014, 8, 9332-9340. (13)

Briscoe, J., Stewart, M., Vopson, M., Cain, M., Weaver, P. M., Dunn, S., Nanostructured

P-N Junctions for Kinetic-to-Electrical Energy Conversion. Adv. Energy Mater. 2012, 2, 12611268. (14)

Zhai, T. Y., Li, L., Ma, Y., Liao, M. Y., Wang, X., Fang, X. S., Yao, J. N., Bando, Y.,


23


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

Page 24 of 30

Golberg, D., One-Dimensional Inorganic Nanostructures: Synthesis, Field-Emission and Photodetection. Chem. Soc. Rev. 2011, 40, 2986-3004. (15)

Liu, G., Hoivik, N., Wang, X., Lu, S., Wang, K., Jakobsen, H., Photoconductive, Free-

Standing Crystallized TiO2 Nanotube Membranes. Electrochim. Acta 2013, 93, 80-86. (16)

Jin, Y., Wang, J., Sun, B., Blakesley, J. C., Greenham, N. C., Solution-Processed

Ultraviolet Photodetectors Based on Colloidal ZnO Nanoparticles. Nano Lett. 2008, 8, 16491653. (17)

Fang, X. S., Yan, J., Hu, L. F., Liu, H., Lee, P. S., Thin SnO2 Nanowires with Uniform

Diameter as Excellent Field Emitters: A Stability of More Than 2400 Minutes. Adv. Funct. Mater. 2012, 22, 1613-1622. (18)

Liu, H., Gao, N., Liao, M. Y., Fang, X. S., Hexagonal-Like Nb2O5 Nanoplates-Based

Photodetectors and Photocatalyst with High Performances. Sci. Rep. 2015, 5, 7716. (19)

Tsai, T.-Y., Chang, S.-J., Weng, W.-Y., Hsu, C.-L., Wang, S.-H., Chiu, C.-J., Hsueh, T.-J.,

Chang, S.-P., A Visible-Blind TiO2 Nanowire Photodetector. J. Electrochem. Soc. 2012, 159, J132-J135. (20)

J. Zou, Q. Zhang, K. Huang, Marzari, N., Ultraviolet Photodetectors Based on Anodic

TiO2 Nanotube Arrays. J. Phys. Chem. C 2010, 114 10725-10729. (21)

Tang, H., Prasad, K., Sanjinès, R., Schmid, P. E., Lévy, F., Electrical and Optical

Properties of TiO2 Anatase Thin Films. J. Appl. Phys. 1994, 75, 2042-2047. (22)

Cheng, H., Selloni, A., Surface and Subsurface Oxygen Vacancies in Anatase TiO2 and

Differences with Rutile. Phys. Rev. B 2009, 79, 2101. (23)

Lee, K., Mazare, A., Schmuki, P., One-Dimensional Titanium Dioxide Nanomaterials:

Nanotubes.Chem Rev. 2014, 114, 9385-9454.


24

Page 25 of 30

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)

Roy, P., Berger, S., Schmuki, P., TiO2 Nanotubes: Synthesis and Applications.Angew.

Chem. Int. Ed. 2011, 50, 2904-2939. (25)

Li, H., Chen, Z., Tsang, C. K., Li, Z., Ran, X., Lee, C., Nie, B., Zheng, L., Hung, T., Lu,

J., Pan, B., Li, Y. Y., Electrochemical Doping of Anatase TiO2 in Organic Electrolytes for HighPerformance Supercapacitors and Photocatalysts. J. Mater. Chem. A 2014, 2, 229-236. (26)

Zheng, L. X., Cheng, H., Liang, F., Shu, S., Tsang, C. K., Li, H., Lee, S.-T., Li, Y. Y.,

Porous TiO2 photonic Band Gap Materials by Anodization. J. Phys. Chem. C 2012, 116, 55095515. (27)

Jennings, J. R., Ghicov, A., Peter, L. M., Schmuki, P., Walker, A. B., Dye-Sensitized Solar

Cells Based on Oriented TiO2 Nanotube Arrays: Transport, Trapping, and Transfer of Electrons. J. Am. Chem. Soc. 2008, 130, 13364-13372. (28)

Wang, L., Yang, W., Chong, H., Wang, L., Gao, F., Tian, L., Yang, Z., Efficient

Ultraviolet Photodetectors Based on TiO2 Nanotube Arrays with Tailored Structures. RSC Adv. 2015, 5, 52388-52394. (29)

El Ruby Mohamed, A., Rohani, S., Modified TiO2 Nanotube Arrays (TNTAs):

Progressive Strategies Towards Visible Light Responsive Photoanode, A Review. Energy Environ. Sci. 2011, 4, 1065. (30)

Xie, Y., Wei, L., Li, Q., Wei, G., Wang, D., Chen, Y., Jiao, J., Yan, S., Liu, G., Mei, L.,

Self-Powered Solid-State Photodetector Based on TiO2 Nanorod/Spiro-MeOTAD Heterojunction. Appl. Phys. Lett. 2013, 103, 261109. (31)

Peng, L., Hu, L. F., Fang, X. S., Energy Harvesting for Nanostructured Self-Powered

Photodetectors. Adv. Funct. Mater. 2014, 24, 2591-2610. (32)

Tang, Q., Lin, L., Zhao, X., Huang, K., Wu, J., P-N Heterojunction on Ordered ZnO


25


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

Page 26 of 30

Nanowires/Polyaniline Microrods Double Array. Langmuir 2012, 28, 3972-3978. (33)

Yang, S., Gong, J., Deng, Y., A Sandwich-Structured Ultraviolet Photodetector Driven

Only by Opposite Heterojunctions. J. Mater. Chem. 2012, 22, 13899-13902. (34)

Yang, S., Yang, H., Ma, H., Guo, S., Cao, F., Gong, J., Deng, Y., Manganese Oxide

Nanocomposite Fabricated by a Simple Solid-State Reaction and Its Ultraviolet Photoresponse Property. Chem. Commun. 2011, 47, 2619-2621. (35)

Prakasam, H. E., Shankar, K., Paulose, M., Varghese, O. K., Grimes, C. A., A New

Benchmark for TiO2 Nanotube Array Growth by Anodization. J. Phys. Chem. C 2007, 111, 72357241. (36)

Zheng, L. X., Teng, F., Zhang, Z. M., Zhao, B., Fang, X. S., Large Scale, Highly Efficient

and Self-Powered UV Photodetectors Enabled by All-Solid-State n-TiO2 Nanowell/p-NiO Mesoporous Nanosheet Heterojunctions. J. Mater. Chem. C 2016, 4, 10032-10039. (37)

Fan, H., Wang, H., Zhao, N., Zhang, X., Xu, J., Hierarchical Nanocomposite of

Polyanilinenanorods Grown on the Surface of Carbon Nanotubes for High-Performance Supercapacitor Electrode.. J. Mater. Chem. 2012, 22, 2774-2780. (38)

Zheng, L. X., Han, S. C., Liu, H., Yu, P. P., Fang, X. S., Hierarchical MoS2 Nanosheet@

TiO2 Nanotube Array Composites with Enhanced Photocatalytic and Photocurrent Performances. Small 2016, 12, 1527-1536. (39)

Xie, Y., Xia, C., Du, H., Wang, W., Enhanced Electrochemical Performance of

Polyaniline/Carbon/Titanium Nitride Nanowire Array for Flexible Supercapacitor. J. Power Sources 2015, 286, 561-570. (40)

Li, Z., Xin, Y., Zhang, Z., Colorful Titanium Oxides: A New Class of Photonic Materials.

Nanoscale 2015, 7, 19894-19898.


26

Page 27 of 30

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


(41)

Tang, Q., Wu, J., Sun, X., Li, Q., Lin, J., Shape and Size Control of Oriented Polyaniline

Microstructure by a Self-Assembly Method. Langmuir 2009, 25, 5253-5257. (42)

Ansari, M. O., Khan, M. M., Ansari, S. A., Raju, K., Lee, J., Cho, M. H., Enhanced

Thermal Stability under Dc Electrical Conductivity Retention and Visible Light Activity of Ag/ TiO2@Polyaniline Nanocomposite Film. ACS Appl. Mater. Interfaces 2014, 6, 8124-8133. (43)

Wang, H., Yi, G., Zu, X., Jiang, X., Zhang, Z., Luo, H., A Highly Sensitive and Self-

Powered Ultraviolet Photodetector Composed of Titanium Dioxide Nanorods and Polyaniline Nanowires. Mater. Lett. 2015, 138, 204-207. (44)

Zhao, B., Wang, F., Chen, H. Y., Wang, Y., Jiang, M., Fang, X. S., Zhao, D. X., Solar-

Blind Avalanche Photodetector Based on Single ZnO-Ga2O3 Core-Shell Microwire. Nano Lett. 2015, 15, 3988-3993. (45)

Liu, S., Wei, Z., Cao, Y., Gan, L., Wang, Z., Xu, W., Guo, X., Zhu, D., Ultrasensitive

Water-Processed Monolayer Photodetectors. Chem. Sci. 2011, 2, 796. (46)

Li, L., Fang, X. S., Zhai, T. Y., Liao, M. Y., Gautam. U. K., Wu, X. C., Koide, Y., Bando,

Y., Golberg, D., Electrical Transport and High-Performance Photoconductivity in Individual ZrS2 Nanobelts. Adv. Mater. 2010, 22, 4151–4156. (47)

Hussain, A. A., Sharma, B., Barman, T., Pal, A. R., Self-Powered Broadband

Photodetector Using Plasmonic Titanium Nitride. ACS Appl. Mater. Interfaces 2016, 8, 42584265. (48)

Xiang, D., Han, C., Hu, Z., Lei, B., Liu, Y., Wang, L., Hu, W. P., Chen, W., Surface

Transfer Doping-Induced, High-Performance Graphene/Silicon Schottky Junction-Based, SelfPowered Photodetector. Small 2015, 11, 4829-4836. (49)

Hong, Q., Cao, Y., Xu, J., Lu, H., He, J., Sun, J. L., Self-Powered Ultrafast Broadband


27


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

Page 28 of 30

Photodetector Based on P-N Heterojunctions of Cuo/Si Nanowire Array. ACS Appl. Mater. Interfaces 2014, 6, 20887-20894. (50)

Zhao, C., Liang, Z., Su, M., Liu, P., Mai, W., Xie, W., Self-Powered, High-Speed and

Visible-near Infrared Response of MoO3-X/n-Si Heterojunction Photodetector with Enhanced Performance by Interfacial Engineering. ACS Appl. Mater. Interfaces 2015, 7, 25981-25990. (51)

Hu, K.; Chen, H. Y.; Jiang, M. M.; Teng, F.; Zheng, L. X.; Fang, X. S., Broadband

Photoresponse Enhancement to High Performance t-Se Microtube Photodetector by Plasmonic Metallic Nanoparticles. Adv. Funct. Mater. 2016, 26, 6641-6648. (52)

Chen, H. Y., Liu, K. W., Chen, X., Zhang, Z., Fan, M., Jiang, M., Xie, X., Zhao, H.,

Shen, D. Z., Realization of a Self-Powered ZnO MSM UV Photodetector with High Responsivity Using an Asymmetric Pair of Au Electrodes. J. Mater. Chem. C 2014, 2, 96899694. (53)

Liu, H., Zhang, Z. M., Hu, L. F., Gao, N., Sang, L. W., Liao, M. Y., Ma, R. Z., Xu, F. F.,

Fang, X. S., New UV-A Photodetector Based on Individual Potassium Niobate Nanowires with High Performance. Adv. Opt. Mater. 2014, 2, 771-778. (54)

Zu, X., Wang, H., Yi, G., Zhang, Z., Jiang, X., Gong, J., Luo, H., Self-Powered UV

Photodetector Based on Heterostructured TiO2 Nanowire Arrays and Polyaniline Nanoflower Arrays. Synthetic Met. 2015, 200, 58-65. (55)

Mridha, S., Basak, D., Zno/Polyaniline Based Inorganic/Organic Hybrid Structure:

Electrical and Photoconductivity Properties. Appl. Phys. Lett. 2008, 92, 142111. (56)

Shao, D., Yu, M., Sun, H., Xin, G., Lian, J., Sawyer, S., High-Performance Ultraviolet

Photodetector Based on Organic-Inorganic Hybrid Structure. ACS Appl. Mater. Interfaces 2014, 6, 14690-14694.


28

Page 29 of 30

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


(57)

Yang, S., Cui, X., Gong, J., Deng, Y., Synthesis of TiO2-Polyaniline Core-Shell

Nanofibers and Their Unique Uv Photoresponse Based on Different Photoconductive Mechanisms in Oxygen and Non-Oxygen Environments. Chem. Commun. 2013, 49, 4676-4678.


29


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