High performance dye-sensitized solar cells using graphene modified fluorine-doped tin oxide glass by Langmuir–Blodgett technique

https://doi.org/10.1016/j.jssc.2014.04.022Get rights and content

Highlights

  • By LB technique, r-GO sheets were coated on FTO without physical deformation.

  • DSSCs were fabricated with, r-GO modified FTO substrates.

  • With surface modification by r-GO, the interface resistance of DSSC decreased.

  • Maximum PCE of the DSSC was increased up to 8.44%.

Abstract

Since the introduction of dye-sensitized solar cells (DSSCs) with low fabrication cost and high power conversion efficiency, extensive studies have been carried out to improve the charge transfer rate and performance of DSSCs. In this paper, we present DSSCs that use surface modified fluorine-doped tin oxide (FTO) substrates with reduced graphene oxide (r-GO) sheets prepared using the Langmuir–Blodgett (LB) technique to decrease the charge recombination at the TiO2/FTO interface. R-GO sheets were excellently attached on FTO surface without physical deformations such as wrinkles; effects of the surface coverage of r-GO on the DSSC performance were also investigated. By using graphene modified FTO substrates, the resistance at the interface of TiO2/FTO was reduced and the power conversion efficiency was increased to 8.44%.

Graphical abstract

DSSCs with graphene modified FTO glass were fabricated with the Langmuir Blodgett technique. GO sheets were transferred to FTO at various surface pressures in order to change the surface density of graphene and the highest power conversion efficiency of the DSSC was 8.44%.

  1. Download : Download high-res image (248KB)
  2. Download : Download full-size image

Introduction

Since they were introduced by the Grätzel group, dye-sensitized solar cells (DSSCs) have received interest for their high power conversion efficiency (PCE) and low fabrication costs [1], [2], [3]. One of the key considerations for preparing high performance DSSCs is to transport photoelectrons generated from the dye molecules to the collecting electrode while competing the charge recombination. DSSCs typically consist of a Pt counter-electrode, I/I3− liquid electrolyte, TiO2 mesoporous particle films covered with dye molecules and transparent conducting glass such as fluorine-doped tin oxide (FTO) glass [1], [4]. During the transportation of electrons in DSSC, the various interfaces between the materials mentioned above play important roles because they simultaneously act as electron transit paths and predominant locations for charge/hole recombination [5], [6].

Therefore, much attention has been paid to this area in extensive research to improve PCE by surface modification of photo- and counter-electrodes that has been carried out [7], [8], [9], [10], especially using methods that can fabricate addition coatings on the FTO glass, such as the deposition of a thin TiO2 layer by TiCl4 pre-treatment [11], [12], [13]. Recently, the research into coating FTO with two-dimensional (2D) structured graphene sheets has begun to improve the performance of DSSC by retarding the recombination at the interface of TiO2/FTO. Chen et al. reported a PCE of 8.1% using graphene-functionalized FTO and graphene/TiO2 composite anodes [14]; however, graphene sheets prepared by spin-coating in their report showed a few wrinkles and the resulting physically poor contact of the graphene with the FTO glass could affect the electron transport. Hence, cell performance would be further improved if a novel method to enhance graphene sheet adhesion on FTO were introduced.

In this paper, we coated reduced graphene oxide (r-GO) sheets on FTO glass without surface deformation using the Langmuir–Blodgett (LB) assembly technique to reduce the charge recombination at the TiO2/FTO interface. Since the LB technique is a typical process for forming a monolayer coating on substrates, it could be an ideal approach to achieve a large and flat area of single layer graphene films [15]. The distribution density of r-GO was tuned using different surface pressures and a high efficiency of 8.44% was achieved using only surface modified FTO with r-GO. Light harvesting and charge recombination kinetics are characterized using a solar simulator and electrochemical impedance spectroscopy (EIS) analysis.

Section snippets

Experimental

Colloidal graphene oxide (GO) has generally been prepared by oxidation of graphite powder using a modified Hummers׳ method [16]. In the first step, graphite (Alfa Aesar, UCP-1 grade), K2S2O8, and H2SO4 were stirred together in an 80 °C oil bath for the pre-oxidation process. Then, for the oxidation process, KMnO4 was slowly added in a 30 °C oil bath. This solution was transferred to an ice bath and formed a thick paste. Next, distilled water was carefully added, and the solution was stirred for 30

Results and discussion

We first deposited GO sheets on silicon wafers using the LB technique and observed sheets with AFM. It can be seen that the lateral dimensions of GO sheets were in the range of 0.5–3.0 μm; the line scan in Fig. 1b shows that the average thickness of the sheet was around 1 nm. These results confirm that 2D GO sheets were successfully synthesized from flake graphite using the modified Hummers’ method. GO coated FTO glass was also prepared by using the same LB dip-coating with a surface pressure of

Conclusions

We have demonstrated an effective method to deposit r-GO sheets on FTO glass without physical deformations using the LB technique. GO sheets were transferred to FTO at various surface pressures in order to change the surface density of r-GO; an excellent adhesion of the sheets to FTO was observed by SEM. DSSCs prepared using r-GO modified FTO substrates showed better performance than did those without pre-modification of r-GO. With the r-GO modification, the values of Rs and R2 of the DSSCs

Acknowledgments

This research was supported by the General Research Project of the Korea Institute of Geoscience and Mineral Resources (KIGAM), funded by the Ministry of Science, ICT and Future Planning.

References (21)

  • J. Yu et al.

    J. Power Sources

    (2011)
  • V. Thavasi et al.

    Mater. Sci. Eng., R

    (2009)
  • S. Ito et al.

    Thin Solid Films

    (2008)
  • T. Sawatsuk et al.

    Diamond Relat. Mater.

    (2009)
  • H. Xu et al.

    Electrochim. Acta

    (2010)
  • J. Xi et al.

    Electrochim. Acta

    (2011)
  • M.-S. Wu et al.

    Electrochim. Acta

    (2011)
  • B. O’Regan et al.

    Nature

    (1991)
  • M. Grätzel

    Acc. Chem. Res.

    (2009)
  • J.G. Yu et al.

    Nanoscale

    (2010)
There are more references available in the full text version of this article.

Cited by (14)

  • Recent development in two-dimensional material-based advanced photoanodes for high-performance dye-sensitized solar cells

    2023, Solar Energy
    Citation Excerpt :

    Graphene with Pt or Ni grids, rGO with FTO or ZnO, and graphene-like carbon or GNPLs with FTO have been studied. The results show that the use of rGO/FTO as the TCO in DSSC photoanodes can provide the highest PCE (8.44 %) compared with other materials (Chen, T. et al., 2012b; Muchuweni et al., 2020; Neo and Ouyang, 2013; Roh et al., 2015; Shahid et al., 2017). Therefore, further efforts have been made to improve rGO/FTO-based photoanodes in DSSCs.

  • Linking bridge improvement of ZnO/N719 interfaces via ammonia treatment for efficiency enhancement of dye-sensitized solar cell

    2021, Surfaces and Interfaces
    Citation Excerpt :

    This result implies a longer movement lifetime of the excited electrons in the conduction band of ZnO in the treated-film devices (as also reflected by the larger Rct2 in the EIS result). The large Rct2 and slow decay of the time-dependent Voc indicate either that electron recombination was suppressed [23] or that electron transport was enhanced at the ZnO/dye/electrolyte interfaces [24,25]. These behaviors imply that treatment improved the linkage between the dye molecules and ZnO films, thus facilitating electron transport and reducing electron recombination in the DSSC devices [21,26,27].

  • Electrophoretic deposition of graphene nanosheets: A suitable method for fabrication of silver-graphene counter electrode for dye-sensitized solar cell

    2017, Colloids and Surfaces A: Physicochemical and Engineering Aspects
    Citation Excerpt :

    Generally, defects and functional groups have critical effects on the electrocatalytic behavior of graphene and graphene oxide; especially by considering their effect on electrostatic interaction between the electrode’s surface and the redox couples in the electrolyte medium [25,26]. The hydrophilicity of exfoliated GO nanosheets which is due to its oxygen-rich functional groups like hydroxyl OH, carboxyl COOH, epoxide and carbonyl CO moieties, primarily facilitates film coating on the hydrophilic RCA-treated FTO, during the EPD procedure [23,26]. However, higher concentration of oxidized functionalities causes quiet sluggish electrochemical activity toward the iodine species [27].

  • Effect of ion doping on catalytic activity of MWCNT-polyaniline counter electrodes in dye-sensitized solar cells

    2016, Materials and Design
    Citation Excerpt :

    However, Pt is an expensive noble metal [7–10]. Therefore, extensive explorations have been made to find other low-cost catalytic materials that could potentially be used, including carbonaceous materials, conductive polymers, transition metal compounds, and alloy materials such as carbon black [11], carbon nanotubes [12], graphene [13,14], porous carbons [15,16], mesoporous carbon-graphene composite Film [17], polypyrrole (PPy) [18,19], poly(3.4-ethylenedioxythiophene) (PEDOT) [20], polyaniline (PANI) [21], carbide [22], nitride [23], oxide [24], sulphide [25], phosphide [26], silicide [27], multiple compounds [28,29] and alloys [30,31]. Recently, the use of composite CE materials such as VC/carbon, MoS2/graphene, and PEDOT/exfoliated graphite were demonstrated to allow achievement of high catalytic activity, [32–34].

  • Carbon Nanotubes and Graphene in Photovoltaics

    2023, Emerging Applications of Carbon Nanotubes and Graphene
View all citing articles on Scopus
1

These authors are equally contributed to this paper.

View full text