Elsevier

Synthetic Metals

Volume 200, February 2015, Pages 58-65
Synthetic Metals

Self-powered UV photodetector based on heterostructured TiO2 nanowire arrays and polyaniline nanoflower arrays

https://doi.org/10.1016/j.synthmet.2014.12.030Get rights and content

Highlights

  • Polyaniline nanoflower array on TiO2 nanowire array was synthesized.

  • The morphology and thickness of polyaniline layer can be adjusted.

  • The sandwich-structured UV photodetectors had good UV sensitivity at 0 V bias.

  • Intensity of photocurrent increased with the thickness of PANI layer increasing.

  • The sandwich-structured UV photodetectors is low cost.

Abstract

A novel self-powered ultraviolet (UV) photodetector with low cost and large area was successfully constructed which was composed of heterostructured arrays of TiO2 nanowires (NWs)/polyaniline nanoflowers (PANI NFs)/TiO2 NWs. The heterostructured arrays of TiO2 NWs/PANI NFs/TiO2 NWs were prepared by combining the hydrothermal and in-situ multiple wet chemical deposition methods. The control methods for the morphology and thickness of PANI on TiO2 NW array were systematically investigated, and their application in UV photodetector was discussed. The results showed that PANI NFs on TiO2 NW array could be obtained by multiple deposition method, and the thickness of PANI NF layer can be adjusted. Furthermore, compared with bare TiO2 NW array, the sensitivity and photocurrent of the UV photodetectors based on TiO2 NWs/PANI NFs/TiO2 NWs heterostructured arrays were both improved greatly at 0 V bias due to the two heterojunctions of n-type TiO2 NWs and p-type PANI NFs, and the intensity of photocurrent could be improved with the thickness of PANI layer increasing.

Introduction

As important members of the optoelectronic device family, ultraviolet (UV) photodetectors have attracted considerable attention recently due to their applications in scientific, military, and commercial applications, for example, UV astronomy, missile early warning, UV imaging, flame detection, environmental and biological research, etc [1], [2], [3], [4]. Generally, most of the traditional photodetectors need an external power sources, such as batteries and other energy storage/supply systems, which not only largely increase the system size but also greatly limit their mobility and independence for applications [5], [6], [7], [8], [9], [10]. For a large-area nanosystem that contain huge numbers of small UV photodetectors, energy supply will be one of the main challenges. In fact, the purpose of using external power sources is to provide potential difference as driving force to restrain the recombination of the photogenerated electron–hole pairs and generate photocurrent. In terms of the charge separation features of the interface, the self-powered photodetectors have basically three structure types: p–n junction type [11], [12], [13], [14], Schottky junction type [5], [15], [16] and photoelectrochemical type [17], [18]. Self-powered photodetectors based on p–n junctions have particularly received a great deal of attention due to their ability to control the directional movement of the photogenerated electrons and causes the generation of photocurrent. So far, great effort has been made to improve the performance of the self-powered p–n junction type photodetectors. For example, Yang et al. [11] fabricated a UV photodetector composed of ZnO NWs/polyaniline nanofibers p–n and PANI nanofibers/ZnGa2O4 film type-II heterojunctions. Though the UV photodetectors could generate opposite photocurrent when illuminated at different wavelengths, the highest photocurrent value was only in the region of 10−7 A at 0 V bias. Our group [12] also reported a self-powered UV photodetector driven only by opposite ZnO/PANI heterojunctions, and showed good sensitivity to UV light at a bias of 0 V. However, it can not work well in acid environment and the PANI layer can not be prepared by in-situ deposition method, because the ZnO layer can be dissolved in acid solution. Thus, it can be seen that fabrication of high performance and self-powered UV photodetectors still remains a challenge.

In recent years, UV photodetectors based on semiconductor nanomaterials, such as TiO2 [17], [18], [19], ZnO [20], [21], [22], [23], SnO2 [7], [24], ZnS [6], [25], BiOBr [26], GaN [8], [27] and Ga2O3 [28], etc, as building blocks have been investigated. In particular, nanostructural TiO2 has been intensively studied as functional parts in UV photodetectors because of its low cost, abundance, non-toxicity, structural stability and good optoelectronic properties [29], [30], [31]. Hussain et al. reported a solar-blind flexible ultraviolet photodetector using nanocomposite film of plasma polymerized aniline-titanium dioxide [29]. Furthermore, one-dimensional single-crystalline TiO2 has been intensively investigated due to the greatly enhanced electrochemical properties and large specific surface area. Cao et al. reported a UV sensor based on TiO2 nanorod arrays [19]. Han et al. reported a self-powered, visual and self-recovered UV photodetector by combining Pt-modified TiO2 nanotubes and Prussian blue (PB)-modified ITO, in which the existence of UV could be judged easily by naked eye with the aid of PB for electrochromic display [17]. Yang et al. reported an UV photoresponse based on TiO2-PANI core–shell nanofibers, and its photocurrent was about 1.9 μA at 0.01 V bias in an environment without O2 [32]. However, self-powered UV photodetectors with a high tolerance of acid conditions based on TiO2 NWs and PANI NFs heterostructured arrays have not been reported. Particularly, low cost and convenient preparation of large-area TiO2 NWs and PANI NFs heterostructured arrays have not been reported.

Herein, we report a low cost and simple method to fabricate acid tolerant and self-powered UV photodetectors based on heterostructured arrays of TiO2 NWs/PANI NFs/TiO2 NWs made by the combination of the hydrothermal and in-situ multiple wet chemical deposition methods. They can work without any bias voltage due to the build-in electric field formed by two heterojunctions. Scheme 1 shows a schematic illustration of the fabrication of TiO2 NWs/PANI NFs/TiO2 NWs heterostructured arrays. Firstly, highly oriented n type TiO2 NW array was grown on fluorine doped tin oxide (FTO) glass substrate by the hydrothermal method. Then, p-type PANI was deposited on as-grown TiO2 NW array by in-situ wet chemical deposition method at about 0–5 °C. In order to control the thickness and morphology of PANI layer, the reaction solution was changed to fresh solution per hour for depositing multiple times. After that, another as-grown TiO2 NW array was covered on TiO2 NWs/PANI NFs heterostructured arrays face to face to obtain the heterostructured arrays of TiO2 NWs/PANI NFs/TiO2 NWs.

Section snippets

Materials

Aniline(C6H7N, 99+%), ammonium peroxyd sulfate (APS, 98%) and poly(styrene sulfonic acid) sodium salt(PSS, M.W. 70000) were purchased from Alfa Aesar. Titanium butoxide([CH3(CH2)3O]4Ti, 98%) was purchased from Tianjin Fuchen Chemical Reagents Factory. Hydrochloric acid (analytical grade) was purchased from Guangzhou Chemical Reagent No. 2 Factory. Absolute ethanol (analytical grade) was purchased from Tianjin Yongda Chemical Reagent Co. Ltd. FTO substrates were purchased from Nippon Sheet Glass

Results and discussion

TiO2 NW array was prepared on FTO glass from a hydrothermal method grown at 150 °C for 20 h. Fig. 1 shows the morphologies of the as-grown TiO2 NWs on FTO glass substrate. It is clearly seen from the low-magnification image in Fig. 1a that the high-aspect-ratio TiO2 NWs are grown in very high density over the whole substrate surface. The high- magnification image in Fig. 1a shows that the TiO2 NWs are tetragonal in shape with square top facets. The top surface of the TiO2 nanowires appears to

Conclusion

In conclusion, we have successfully fabricated a low cost, acid tolerant and high-performance self-powered UV photodetector based on TiO2 NWs/PANI NFs/TiO2 NWs heterostructured arrays which was prepared by combining hydrothermal and in-situ wet chemical deposition methods. And the morphology and thickness of PANI on TiO2 NW array can be adjusted by repeating wet chemical deposition for different times. The resulting photodetector exhibited excellent UV sensitivity and fast response speed with

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grant No. 51203025, 51273048 and 51203191), the Natural Science Foundation of Guangdong province (Grant No. S2012040007725) and Foundation for Distinguished Young Talents in Higher Education of Guangdong, China (2012LYM-0059). X. Zu and H. Wang have contributed equally to this work.

References (34)

  • Z.M. Bai et al.

    Prog. Nat. Sci.

    (2014)
  • C.L. Cao et al.

    Sens. Actuators B

    (2011)
  • G.H. Liu et al.

    J. Alloys Comp.

    (2014)
  • Y.N. Hou et al.

    Appl. Phys.

    (2013)
  • D.L. Shao et al.

    Nanotechnology

    (2013)
  • B.C. Cheng et al.

    Opt. Express

    (2013)
  • Q. Li et al.

    Analyst

    (2012)
  • Z.M. Bai et al.

    Phys. Chem. Chem. Phys.

    (2014)
  • W. Tian et al.

    Adv. Mater.

    (2014)
  • W. Tian et al.

    Adv. Mater.

    (2013)
  • X. Li et al.

    Appl. Phys. Lett.

    (2014)
  • D.L. Shao et al.

    Nanoscale

    (2013)
  • J.W. Liu et al.

    Adv. Funct. Mater.

    (2013)
  • S.X. Yang et al.

    Appl. Phys. Lett.

    (2013)
  • S.X. Yang et al.

    J. Mater. Chem.

    (2012)
  • Y.Q. Bie et al.

    Adv. Mater.

    (2011)
  • O. Game et al.

    Nanoscale

    (2014)
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