Polymer 230 (2021) 124092 Available online 9 August 2021 0032-3861/© 2021 Elsevier Ltd. All rights reserved. Chitosan as a paradigm for biopolymer electrolytes in solid-state dye-sensitised solar cells Noriah Abdul Rahman a , Sharina Abu Hanifah a, b , Nadhratun Naiim Mobarak a, b , Azizan Ahmad a, b, c , Norasikin Ahmad Ludin d , Federico Bella e, * , Mohd Sukor Su’ait d, ** a Department of Chemical Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600, Bangi, Selangor Darul Ehsan, Malaysia b Polymer Research Center (PORCE), Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600, Bangi, Selangor Darul Ehsan, Malaysia c Research Center for Quantum Engineering Design, Faculty of Science and Technology, Universitas Airlangga, 60115, Surabaya, Indonesia d Solar Energy Research Institute (SERI), Universiti Kebangsaan Malaysia, 43600, Bangi, Selangor Darul Ehsan, Malaysia e Electrochemistry Group, Department of Applied Science and Technology, Politecnico di Torino, 10129, Turin, Italy A R T I C L E INFO Keywords: Biopolymer electrolyte Chitosan Dye-sensitised solar cell Solid-state electrolyte Biosourced polymer Solid-state photovoltaics ABSTRACT Biopolymers are among the most promising electrolyte hosts for different electrochemical devices in the energy conversion and storage felds. In this work, the potential of chitosan as a biopolymer laden with NaI salt is explored and applied as solid polymer electrolyte for dye sensitised solar cells. The chitosan-NaI electrolyte is successfully prepared via a simple and upscalable solution casting technique. Infrared spectroscopy analysis highlights interactions between chitosan and NaI, that weaken the semi-crystalline domains of chitosan and favour the conduction of the redox shuttle ions between cell electrodes. At room temperature, the best ionic conductivity was obtained for the samples laden with NaI 30 wt%, with values equal to 1.11 × 10 4 S cm 1 . Na + transference number determination indicates that only 0.9% of the ionic conductivity is determined by these cations, thus highlighting that I  anions represent the active species in the newly proposed solid-state electrolyte. This result is highly desired considering that these anions are those responsible for the regeneration of oxidized dye molecules in the cell and, overall, for the cell effciency. Current-voltage measurement of solid-state photovoltaic devices under simulated sunlight led to a reproducible and stable power conversion effciency of 0.06%, along with a short-circuit current density of 0.32 mA cm 2 , an open circuit voltage of 0.7 V and a fll factor 0.3. 1. Introduction Solar cells are getting every day more attention due to issues like the pollution and shortage of energy sources from carbon-based fuels [1,2]. Solar energy can be the promising future energy source since it is abundant, clean, safe and silent [3–6]. Dye-sensitised solar cells (DSSCs), famously known as Gr¨ atzel cells, are categorised as an emerging generation of solar cell possessing low manufacturing cost, high conversion effciency and simple preparation technique [7,8]. Most of the DSSCs with high effciency up to ≈14% use liquid electrolytes (LEs), typically based on organic solvents solubilizing a redox shuttle [9, 10]. Although these LEs lead to high effciency values, they cause rele- vant issues such as leakage, diffculties in sealing and fabrication pro- cesses, safety problems and corrosion of metal components, leading to an overall poor long-term stability [11]. Therefore, solid polymer elec- trolytes (SPEs) represent a strong solution to this issue and are now considered as a Holy Grail in the feld of DSSCs, since they would be able to freeze the degradation of cell performance upon time [12,13]. SPEs consisting of complexes of alkali metal ions within a polymeric matrix were proposed by Fenton and Wright [14]. They used sodium- and potassium-based salts and poly(ethylene oxide) (PEO) for the preparation of the frst polymer electrolytes. The research on SPEs has continued and today is a cutting edge topic in the feld of solid-state electrochemistry [15,16]. SPEs are able to form good interfaces with electrodes surfaces and they are leakage-free, easy to seal and typically show wide electrochemical stability windows [17]. Additionally, SPEs possess desirable properties such as easy assembly of flms in various shapes, sizes and designs, which are suitable for various electrochemical * Corresponding author. ** Corresponding author. E-mail addresses: federico.bella@polito.it (F. Bella), mohdsukor@ukm.edu.my (M.S. Su’ait). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer https://doi.org/10.1016/j.polymer.2021.124092 Received 3 June 2021; Received in revised form 6 August 2021; Accepted 8 August 2021