Elsevier

Journal of Power Sources

Volume 274, 15 January 2015, Pages 937-942
Journal of Power Sources

The construction of tandem dye-sensitized solar cells from chemically-derived nanoporous photoelectrodes

https://doi.org/10.1016/j.jpowsour.2014.10.125Get rights and content

Highlights

  • Fabrication of tandem-DSSCs by simple sputtering deposition and selective etching.

  • Parameters (Voc, Jsc, FF, Rsh, and Rshrecom) fitted with an ideal one-diode model.

  • Successfully-designed tandem construction confirmed by impedance analysis.

Abstract

A tandem dye-sensitized solar cell (tandem-DSSC) was synthesized on the basis of thin-film semiconductor electrodes. The nanoporous p-type NiO films were successfully obtained by simultaneous deposition of Al and Ni, followed by selective etching of Al and oxidation. Likewise, the n-type photoanode was made where Ag was etched in nitric acid after the initial formation of Ag/TiO2 nanocomposites. Such dye-sensitized photoelectrodes were combined to construct a tandem solar cell which exhibited an enhanced open-circuit voltage. Also, the tandem devices were subjected to various light fluxes to correlate the experimental cell parameters (open-circuit voltage, short-circuit current, fill factor, recombination shunt resistance, etc.) with the ideal one-diode model. Interestingly, impedance spectra of the tandem cell was well matched with the parameters from each of the n-type or p-type DSSC, indicative of successfully-designed tandem structure.

Introduction

Dye-sensitized solar cells (DSSCs) have attracted considerable interest as a low cost and renewable means of harnessing solar energy [1], [2]. For this type of device to be competitive to other solar cells, many attempts have been made in terms of enhancing the conversion efficiency [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]. Recently, the concept of ‘tandem-DSSC’ has started evolving where both working and counter electrodes in the DSSC are photoactive [13], [14], [15], [16]. The tandem-DSSC consists of an n-type photoanode linked to a p-type photocathode via the electrolyte, and this configuration can offer improved open-circuit voltage compared to the single-junction (half cell) DSSCs.

For the fabrication of photoelectrodes of DSSCs, doctor-blade method [17] and screen printing [18] of hydrothermally-synthesized TiO2 nanoparticles have been widely used. As another candidate for the photoelectrodes, sputtering deposition has the merits of high uniformity, large-area deposition, and enhanced reproducibility. Therefore, sputtering has been extensively utilized in industrial fields to obtain various coating layers and high-quality functional films, which are typically considered as advantages of dry process sputter deposition [19], [20], [21], [22], [23], [24], [25]. However, electrodes grown by sputtering cannot adsorb a large number of dye molecules, because of the lower specific surface area resulting from the compact nanostructures, compared to the nanoparticle-based films [23], [24]. In order to modify the inefficient surface area, we adopted a selective etching process in sputter-deposited films [26], [27].

In this study, both nanoporous photocathode (NiO) and photoanode (TiO2) were successfully fabricated by simple sputtering deposition and selective etching. Through combining these two electrodes with an intermediate electrolyte layer, we originally suggest sputter-deposited tandem-DSSCs. The photovoltaic properties of tandem-DSSCs were analyzed under various fluxes of the incident light, by comparing the cell parameters in both the experimental and ideal cases. Also, the recombination resistance was investigated with the modified one-diode model to understand the working principles of the tandem-DSSCs. Furthermore, impedance spectra of the tandem cell was correlated with the parameters from each of the n-type or p-type DSSC, to confirm the design of the fabricated tandem structures.

Section snippets

Experimental procedure

To fabricate nanoporous NiO film, Ni–Al alloy films were deposited on fluorine-doped tin oxide (FTO, Pilkington, Japan) substrates by rf magnetron sputtering using Ni and Al targets. Sputtering was performed in an Ar atmosphere with a working pressure of 10 mTorr at room temperature. The optimized sputtering power condition was found to be 40 W for Ni and 160 W for Al. To remove Al from Ni–Al alloy films, the as-deposited Ni–Al alloy films were first immersed in 0.1 M sodium hydroxide (NaOH,

Results and discussion

After the Ni–Al-alloy films being immersed in NaOH, the Ni–Al phase disappeared (diffraction in Fig. S1), indicating a complete removal of Al, and subsequent heat treatment of the as-dealloyed sample led to the crystalline NiO phase. The film morphologies for the before/after dealloying were confirmed by FE-SEM (Fig. S2). The dealloyed-NiO film clearly shows porous characteristics compared to the compact Ni–Al alloy. The porous characteristics of the NiO films were also evaluated by small-angle

Conclusions

The nanoporous electrodes were rendered by a simple chemical dealloying, and they were combined to construct a p-n junction tandem cell. The analysis of recombination resistance from the ideal one-diode model for the flux-dependent J–V curves, together with modeling the impedance spectra provided clues on the principle of the tandem-cell operation. The optimization of tandem-DSSC is a breakthrough challenge to effectively combine two photoactive working and counter electrodes.

Acknowledgments

This research was supported by the National Research Foundation of Korea (NRF): 2013R1A1A2065793 and 2010-0029065.

References (55)

  • J. Kim et al.

    J. Power Sources

    (2011)
  • H. Choi et al.

    Curr. Appl. Phys.

    (2012)
  • J. Kim et al.

    J. Power Sources

    (2012)
  • H. Choi et al.

    Curr. Appl. Phys.

    (2013)
  • B. Hu et al.

    J. Power Sources

    (2014)
  • P. Xu et al.

    Electrochim. Acta

    (2014)
  • J. He et al.

    Sol. Energy Mat. Sol. C

    (2000)
  • M. Gomez et al.

    Sol. Energy Mat. Sol. C

    (1999)
  • S. Takeda et al.

    Thin Solid Films

    (2001)
  • Z. Qi et al.

    J. Power Sources

    (2011)
  • H. Choi et al.

    Nano Energy

    (2013)
  • K. Hara et al.

    Sol. Energy Mat. Sol. C

    (2003)
  • C. Kim et al.

    J. Power Sources

    (2013)
  • A. Jain et al.

    Sol. Energy Mat. Sol. C

    (2004)
  • D.U. Kim et al.

    Sol. Energy Mat. Sol. C

    (2013)
  • F. Fabregat-Santiago et al.

    Sol. Energy Mat. Sol. C

    (2005)
  • B. O'Regan et al.

    Nature

    (1991)
  • M. Grätzel

    Inorg. Chem.

    (2005)
  • S.-J. Roh et al.

    Appl. Phys. Lett.

    (2006)
  • C. Nahm et al.

    Appl. Phys. Lett.

    (2011)
  • E. Palomares et al.

    J. Am. Chem. Soc.

    (2003)
  • Y. Duan et al.

    J. Mater. Chem. A

    (2014)
  • A. Nattestad et al.

    Nat. Mater.

    (2010)
  • E.A. Gibson et al.

    Angew. Chem. Int. Ed.

    (2009)
  • A. Nakasa et al.

    Chem. Lett.

    (2005)
  • S. Ito et al.

    Prog. Photovoltaics

    (2007)
  • M.K. Nazeeruddin et al.

    J. Am. Chem. Soc.

    (1993)
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