Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.elsevier.com/locate/synmet Screen-printed PEDOT:PSS/halloysite counter electrodes for dye-sensitized solar cells Pavol Gemeiner a, ⁎ , Jaroslav Kuliček b , Tomáš Syrový c,d , Aleš Ház e , Viera Khunová f , Michal Hatala a , Milan Mikula a , Matej Hvojnik a , Lukáš Gál a , Michal Jablonský e , Mária Omastová b a Department of Graphic Arts and Applied Photochemistry, Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava, Radlinského 9, 812 37 Bratislava, Slovakia b Polymer Institute, Slovak Academy of Sciences, 845 41 Bratislava, Slovakia c Department of Graphic Arts and Photophysics, Faculty of Chemical Technology, University of Pardubice, Studentská 95, 532 10 Pardubice, Czech Republic d Center of Materials and Nanotechnologies, Faculty of Chemical Technology, University of Pardubice, nám. Cs. legií 565, 53 002 Pardubice, Czech Republic e Department of Wood, Pulp and Paper, Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava, Radlinského 9, 812 37 Bratislava, Slovakia f Department of Plastics, Rubber and Fibres, Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava, Radlinského 9, 812 37 Bratislava, Slovakia ARTICLE INFO Keywords: PEDOT:PSS Halloysite nanotubes Dye-sensitized solar cells Counter electrode Screen-printing Printed electronics ABSTRACT In this work, water-based and viscous screen-printing inks composed of conducting polymer poly(3,4-ethyle- nedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) and insulating halloysite nanotubes as a filler (HNTs) with different organic additives were prepared by simply homogenization process. PEDOT:PSS/HNTs inks were screen-printed onto FTO substrates and were used as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). Incorporation of HNTs leads to a significant increase in ink thermal stability evaluated by TGA. XPS results indicate that simple homogenization process of PEDOT:PSS and HNTs led to the formation of compact PEDOT:PSS/HNTs nanocomposite structure where components are linked by physical interactions. Screen- printed PEDOT:PSS/HNTs CEs with 1 wt% of HNTs reached the highest conductivity (381 S/cm). Moreover, the positive effect of HNTs filler in CEs was confirmed by electrochemical measurements (CV and EIS). DSSCs with screen-printed PEDOT:PSS/HNTs CEs have overall better photovoltaic properties with ≈15% increase in the conversion efficiency (η = 4.5%) compared to PEDOT:PSS CEs. 1. Introduction A dye-sensitized solar cells (DSSCs) belongs to the very promising 3 rd generation of photovoltaics which has several advantages compared to the conventional crystalline silicon-based solar cell such as simple fabrication processes, low-cost materials, the possibility of bifacial il- lumination and high conversion efficiency particularly under low light intensity and diffuse light conditions [1–4]. Moreover, the possibility of using low-cost and environmentally friendly materials which can be prepared in the form of printable inks has a great perspective for broad- scale application of DSSCs on a wide range of plastic and paper flexible or rigid substrates [5]. The standard structure of DSSC is based on the three fundamental components: mesoscopic metal-oxide layer de- posited on TCO (transparent conducting oxide) substrate and sensitized with dye with the function of photoanode (standardly TiO 2 and ru- thenium-based dyes), liquid electrolyte of iodide/triiodide redox couple, and Pt catalytic layer prepared on TCO substrate with the function of counter electrode [1]. The counter electrode (CE) has a key role during the reduction of triiodide to iodide ions, which subsequently regenerate the oxidized dye molecules [6]. Therefore, parameters of CE catalytic layer such as high catalytic activity and conductivity, low charge transfer resistance, high surface area, and transparency, good mechanical and chemical stability have a great impact on the overall performance of DSSC [7,8]. Due to the excellent catalytic activity in the presence of iodide/triiodide electrolyte, the noble metal Pt has been used as the standard and re- ference catalytic layer of CE [9]. However, the high cost, corrosion of Pt in a liquid electrolyte and the requirement of high-temperature post- treatment of Pt CE prepared from printable inks which prevent from its application on the flexible polymeric substrates have been leading to the research of different alternative materials. Among them conducting polymers [6,10], carbon-based nanomaterials [11], transition metal https://doi.org/10.1016/j.synthmet.2019.116148 Received 30 May 2019; Received in revised form 31 July 2019; Accepted 15 August 2019 ⁎ Corresponding author. E-mail address: pavol.gemeiner@stuba.sk (P. Gemeiner). Synthetic Metals 256 (2019) 116148 Available online 04 September 2019 0379-6779/ © 2019 Elsevier B.V. All rights reserved. T