Contents lists available at ScienceDirect Solar Energy journal homepage: www.elsevier.com/locate/solener Polyaniline nanotube/reduced graphene oxide aerogel as efficient counter electrode for quasi solid state dye sensitized solar cell Kiranjyoti Mohan a , Anindita Bora a , Raj Sekhar Roy a , Bikash Chandra Nath b , Swapan Kumar Dolui a, ⁎ a Department of Chemical Sciences, Tezpur University, Napaam, Assam 784028, India b Department of Physics, Tezpur University, Napaam, Assam 784028, India ARTICLE INFO Keywords: Dye sensitized solar cell Graphene based aerogel Polyaniline nanotube Counter electrode ABSTRACT Polyaniline nanotube/reduced graphene oxide aerogel (PAniNT/rGOA) is studied as a potential counter elec- trode material for a quasi-solid-state dye-sensitized solar cell (DSSC) fabricated with poly(methyl methacrylate) based polymer gel electrolyte. The aerogel, prepared via an organic sol–gel route, having a high surface area of 294.73 m 2 g -1 exhibits excellent electro-catalytic activity towards the reduction of triiodide ions in the elec- trolyte. The excellent catalytic activity of the aerogel based electrodes is manifested with cyclic voltammetry based analyses. Electrochemical impedance analyses and current density vs voltage plots are employed to gauze the photovoltaic performance of the DSSCs fabricated with PAniNT/rGOA counter electrode. The thickness of the counter electrode is a crucial factor that affects the performance of the DSSC: thicker films offer more surface area for electro-catalytic reduction reaction whilst increasing the charge and mass transport resistances si- multaneously. At an optimum PAniNT/rGOA electrode film thickness of 8.68 μm, a power conversion efficiency of 5.47% is achieved. In addition, an improvement of open circuit voltage is observed due to the capacitance involved at the electrolyte/electrode interface. 1. Introduction Dye sensitized solar cell (DSSC) has attracted significant attention after its first demonstration by M. Grätzel and B. O’Regan in 1991 due to its high photo-conversion efficiency, easy fabrication technique and low cost (Bach et al., 1998; Grätzel, 2001; O’Regan and Grätzel, 1991). Generally, an electrolyte is sandwiched between a dye adsorbed TiO 2 photoanode and platinum counter electrode to fabricate the DSSC. In the typical structure of DSSC, photon induced oxidation of dye mole- cule occurs at the TiO 2 photoanode, while at the counter electrode re- duction of redox couple helps to regenerate the dye. Usually, iodide and triiodide (I - /I 3 - ) redox couple is used to regenerate the dye molecule (Kebede and Lindquist, 1999; Nasr et al., 1998). Pt as a counter elec- trode material is very popular because it can catalyze the reduction of triiodide ions present in the redox couple. However, high cost and possible chemical degradation of Pt in the corrosive iodine environment demand more cost effective, electrolyte resistance and earth abundant alternatives (Kay and Grätzel, 1996). Conducting polymers, such as polyaniline (PAni), poly(3,4-ethyle- nedioxythiophene) (PEDOT) and polypyrrole have great potential to be used as alternatives for the Pt counter electrode (Bu et al., 2013; Jeon et al., 2011; Trevisan et al., 2011; Wang et al., 2013; Xiao et al., 2012). PAni is considered as one of the most preferred alternatives amongst them because of its low cost, high electrochemical activity and en- vironmental stability. The suitability of PAni as Pt free counter elec- trode was first reported by Li et al. (2008). They prepared microporous PAni with diameter < 100 nm to obtain an efficiency of 7.15% (Li et al., 2008). Since then, many other reports of PAni as counter electrode have been published. For instance, Zhang et al. (2010) grew nanostructured PAni films on fluorine doped tin oxide (FTO) coated glass substrates by employing cyclic voltammetry (CV) technique (Zhang et al., 2010). They obtained an efficiency of 11.6%, which is the highest reported efficiency of a single component PAni based counter electrode device till date. Others have been able to attain efficiencies of 5.19% by using PAni nanofibers prepared by pulse potentiostatic electro-polymeriza- tion of aniline onto FTO coated glass substrate (Xiao et al., 2013), 6.32% by using porous PAni nanobelts (Lan et al., 2014), 6.21% by using PAni nanofibers prepared by two-step CV based electro-poly- merization of aniline onto FTO coated glass substrate (Xiao et al., 2014) and 5.57% by using porous PAni nanotubes (PAniNTs) (Park et al., https://doi.org/10.1016/j.solener.2019.05.030 Received 28 January 2019; Received in revised form 7 May 2019; Accepted 13 May 2019 ⁎ Corresponding author. E-mail address: dolui@tezu.ernet.in (S.K. Dolui). Solar Energy 186 (2019) 360–369 0038-092X/ © 2019 International Solar Energy Society. Published by Elsevier Ltd. All rights reserved. T