Electrochimica Acta 55 (2010) 6731–6742 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Enhanced photoelectrochemistry and interactions in cadmium selenide–functionalized multiwalled carbon nanotube composite films M. Deepa a,∗ , Ruchi Gakhar b , A.G. Joshi b , B.P. Singh b , A.K. Srivastava b a Department of Chemistry, Indian Institute of Technology Hyderabad, Ordnance Factory Estate, Yeddumailaram 502205, Andhra Pradesh, India b National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi 110012, India article info Article history: Received 9 December 2009 Received in revised form 31 March 2010 Accepted 29 May 2010 Available online 8 June 2010 Keywords: Cadmium selenide Multiwalled carbon nanotubes Photoelectrochemical Electrodeposition abstract Cadmium selenide–functionalized multiwalled carbon nanotube (CdSe–f-MWCNT) composite films have been synthesized by the percolation of a f-MWCNT dispersion through the macropores of electrode- posited CdSe thin films during electrophoretic deposition. Evidence for efficient charge transfer from CdSe to f-MWCNTs was obtained by photoluminescence quenching and proof for strong interactions was provided by X-ray photoelectron spectroscopy analyses, which revealed a significant decrease in the reduced Se 2- content and evolution of new signals due to oxidized Se, and high resolution transmission electron microscopy and atomic force microscopy images of CdSe decorated f-MWCNTs in the composite film. Sputter depth profiling of the composite confirmed a homogeneous mixing of nanoparticulate CdSe and f-MWCNTs. A quasi solid-state photoelectrochemical cell fabricated by coupling the composite film with an ionic liquid based gel polymer electrolyte containing the I 3 /I - redox pair not only showed larger photocurrents, photovoltage and incident photon to current conversion efficiency as compared to the analogous CdSe cell but also showed a remarkably enhanced stability to photoerosion. The ability of f- MWCNTs to mediate fast charge transfer and retard charge recombination rate in the composite was also evident from electrochemical impedance spectroscopy (EIS) results. Cell degradation upon exposure was also reflected in the altered EIS parameters such as increased charge transfer resistance and the reduced ease of charge transport through the composite. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction The last decade has witnessed a surge of research interest in designing photoanodes for optimal device performance in photo- electrochemical solar cells. In this context, the interactions between the components play an important role. Relevant aspects include (i) improving the absorption cross-section for efficient solar light harvesting, (ii) identifying the materials which will serve as donors and acceptors and (iii) optimizing the layer and interfacial mor- phologies [1,2]. To this end the most commonly used strategies are to integrate a photoactive compound with a wide gap semicon- ductor like the ruthenium dye adsorbed in mesoscopic titanium dioxide (TiO 2 ) in the dye sensitized solar cells (DSSC) [3–6] or to combine a photosensitive semiconductor with an electron trans- porting scaffold like quantum dots (QDs) in single-walled carbon nanotube (SWCNT) scaffolds or TiO 2 [7,8]. The challenge common to both approaches is to direct the flow of photogenerated electrons efficiently so as to minimize the possibility of their recombination ∗ Corresponding author. Tel.: +91 40 23016053. E-mail address: mdeepa@iith.ac.in (M. Deepa). with the oxidized sensitizer or the oxidized species of the redox couple in the electrolyte. Though dye sensitized solar cells have been investigated exhaustively in the recent years [5,6,9,10], but reports on solid-state photoelectrochemical cells other than DSSC are exceedingly rare. For instance, SWCNTs have been shown to be advantageous for facilitating electron transport in photoelec- trochemical cells [7–9]; but these cells generally make use of liquid electrolytes. But SWCNTs are difficult to process and are expensive [11]. Multiwalled carbon nanotubes (MWCNTs) are comparatively easier to synthesize and purify, have high electronic conductivities and also impart good mechanical integrity to the assembly to which they are introduced [12]. Although the hydrophobic surface of pristine carbon nanotubes (CNTs) can act as a deterrent to its co-deposition with a photoactive material like cadmium selenide (CdSe) but this can be overcome by acid functionalization. Upon functionalization, the oxygen con- taining carboxylate groups not only enable the formation of a processable dispersion of CNTs [13] but also serve as preferable binding sites on the outer walls of the nanotubes for nanoparticu- late CdSe. Here, we report a relatively low cost, facile method for the synthesis of a photoactive composite involving firstly the surfactant mediated electrodeposition of a nanostructured CdSe film, fol- lowed by electrophoretic deposition of functionalized (f)-MWCNTs 0013-4686/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2010.05.097