Construction of 3-dimensional ZnO-nanoflower structures for high quantum and photocurrent efficiency in dye sensitized solar cell

doi:10.1016/j.apsusc.2013.12.065

Applied Surface Science

Volume 318, 1 November 2014, Pages 32-36

https://doi.org/10.1016/j.apsusc.2013.12.065 Get rights and content

Highlights

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The structural and optical characterizations of ZnO nanoflowers were carried out on ITO by hydrothermal method.
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Dye sensitized solar cell based ZnO nanoflowers were constructed on substrate.
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The surface morphology effect on quantum efficiency and solar conversion efficiency were investigated.

Abstract

3-dimensional ZnO nanoflower were obtained on FTO (F:SnO₂) substrate by hydrothermal method in order to produce high efficiency dye sensitized solar cells (DSSCs). We showed that nanoflowers structures have nanoscale branches that stretch to fill gaps on the substrate and these branches of nano-leaves provide both a larger surface area and a direct pathway for electron transport along the channels. It was found that the solar conversion efficiency and quantum efficiency (QE) or incident photon to current conversion efficiencies (IPCE) is highly dependent on nanoflower surface due to high electron injection process. The highest solar conversion efficiency of 5.119 and QE of 60% was obtained using ZnO nanoflowers/N719 dye/I⁻/I⁻₃ electrolyte. In this study, three dimensional (3D)-nanoflower and one dimensional (1D)-nanowires ZnO nanostructures were also compared against each other in respect to solar conversion efficiency and QE measurements. In the case of the 1D-ZnO nanowire conversion efficiency (η) of 2.222% and IPCE 47% were obtained under an illumination of 100 mW/cm². It was confirmed that the performance of the 3D-nanoflowers was better than about 50% that of the 1D-nanowire dye-sensitized solar cells.

Graphical abstract

Introduction

Dye-sensitized solar cells (DSSCs) have attracted much attention in the last decade due to low cost and relatively efficient photovoltaic energy conversion [1], [2], [3]. The highest efficiency, to the best of our knowledge, reported on DSSCs was produced by Gratzel et al. and it was obtained 11% on nanoporous TiO₂ by using ruthenium complex dye, containing I⁻/I⁻₃ redox couple electrolytes and platinum counter electrode [2], [3], [4]. Although the conversion efficiency for TiO₂ are much higher than that achieved with ZnO based cells (0.3–6%), ZnO nano-semiconductor materials are considered as an alternative to TiO₂ due to its ease of crystallization and anisotropic growth [5]. ZnO nanostructures are one of the most promising semiconductor materials for optoelectronic and photonic applications due to its wide, direct band gap (3.37 eV), a large exciton binding energy (60 meV) and a huge magneto-optic effect [6], [7]. Many different ZnO nanostructures have been synthesized under specific experimental conditions and investigated for DSSC applications due to the large specific surface area offered by these nanostructures [8]. The large specific surface area is one of the most important requirements for the photo-electrode films in DSSCs mainly because of the need to maximize dye molecule adsorption on semiconductor materials [9]. Therefore, it was reported that the surface structure, high surface area and the porosity are all important factors for obtain high solar conversion efficiency in DSSCs [10], [11].

Especially, three-dimensional nanoflower and one-dimensional nanowire have attracted great interest for DSSC applications due to their unique optical, electronic, mechanical properties [12], [13], [14], [15]. However, the uses of ZnO nanoflowers consisting of outstretched branches have been also reported for high efficiency in DSSC [16]. This is based on the consideration that the one-dimensional structures may not capture the photons completely due to the existence of intervals inherent in the morphology [16]. Therefore, nanoflower structures have nanoscale branches that stretch to fill these intervals and, provide both a larger surface area and a direct pathway for electron transport along the channels from the branched petals [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17].

In this study, ZnO nanoflowers were growth on FTO substrate by hydrothermal method. X-ray diffraction (XRD) studies of the ZnO nanoflowers showed a high crystallinity and preferred orientation along the (0 0 1) plane of the wurtzite structures. Scanning electron microscopy (SEM) images showed that the nanoflowers can be obtained with average diameters of 10–50 nm and in the range of 1–5 μm in size. Raman spectra of the ZnO nanoflowers showed that the peaks at around 582 cm⁻¹ to be related to the E₁ mode of the ZnO nanoflowers. The room temperature photoluminescence (PL) measurements confirm that the nanoflower samples have near band edge emissions and broad deep level emission. The UV–Visible absorbance spectrums of the ZnO nanoflower show a strong absorption edge between 360 and 400 nm and high transmittance of higher than 92%. As a result, wide band gaps ZnO nanoflowers were successfully used as photoanode in DSSCs and it was compared with one-dimensional nanowire in terms of solar conversion efficiency.

Section snippets

Preparation of ZnO nanoflowers

ZnO nanoflowers were grown on FTO (SnO₂:F), substrate by hydrothermal method using ammonia as the base source. The growth was carried out at 175 °C for 24 h with Zn (NO₃)₂ as a source of Zn²⁺ ions. First of all, FTO substrates were cleaned carefully by dipping for 2 min each in Propan-2-ol, de-ionized water, methanol and de-ionized water, in sequential manner. After the cleaning process, 10 mM Zn(NO₃)₂·6H₂O (aq) solution was prepared and pH of the solution was adjusted to ∼10 using ammonia

Results and discussion

SEM images with different magnification (Fig. 1a–c) show that ZnO nanocrystals with flower-like shapes were successfully obtained uniformly throughout on FTO substrate using an ammonia solution with a pH of 10.0. The diameters of the ZnO nanoflowers were observed to be (from the SEM images) varying between 50 and 1000 nm. When increase in the pH of the solution (pH 11) were obtained ZnO nanowire on substrate as shown before study [11]. The morphology of ZnO obtained from aqueous solution is

Conclusion

The growth of ZnO nanoflower was performed on FTO substrates by hydrothermal method. Structural characterizations showed that the morphology of ZnO nanostructures changed as a function of pH value, from nanoflower (pH 10.0) to nanowire (pH 11.0). The highest solar-to-electric energy conversion efficiency of 5.119% and IPCE of 60% was obtained by using the ZnO nanoflowers/N719 dye/I⁻/I⁻₃ electrolyte. The nanoflowers structures leads to a significant increase of sample conductivity. It was found

Acknowledgment

The authors gratefully acknowledge the Scientific and Technological Research Council of Turkey (TUBITAK) for the grant 2214- PhD research scholarship program.

References (22)

P. Rosenits et al.
Thin Solid Films
(2011)
Z.L. Wang
Mater. Today
(2004)
A. Umar et al.
J. Cryst. Growth
(2005)
A. Yella et al.
Science
(2011)
B.O’ Regan et al.
Nature
(1991)
M.K. Nazereruddin et al.
J. Am. Chem. Soc.
(1993)
Q. Zhang et al.
Adv. Mater.
(2009)
S.H. Lee et al.
Stat. Sol.
(2007)
S. Tüzemen et al.
J. Appl. Phys.
(2006)
A.S. Arico et al.
Nat. Mater.
(2005)

B. Kılıç¸ et al.

J. Nanomater.

(2012)

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View full text

Construction of 3-dimensional ZnO-nanoflower structures for high quantum and photocurrent efficiency in dye sensitized solar cell

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Preparation of ZnO nanoflowers

Results and discussion

Conclusion

Acknowledgment

Thin Solid Films

Mater. Today

J. Cryst. Growth

Science

Nature

J. Am. Chem. Soc.

Adv. Mater.

Stat. Sol.

J. Appl. Phys.

Nat. Mater.

J. Nanomater.