Synthetic Metals 272 (2021) 116659 Available online 17 December 2020 0379-6779/© 2020 Elsevier B.V. All rights reserved. Research paper Electrical impedance spectroscopy study of unsubstituted palladium (II) phthalocyanine A. Timoumi a, b, * , M.A. Wederni c , N. Bouguila d , B. Jamoussi e , M.K. AL Turkestani a , R. Chakroun e , B. Al-Mur e a Department of Physics, Faculty of Applied Science, Umm AL-Qura University, P. O. Box 715, Makkah, Saudi Arabia b LPMS, National Engineering School of Tunis, Belvedere, P. O. Box 37, Tunis 1002, Tunisia c Unit´ e de recherche Mat´ eriaux Avanc´ es et Nanotechnologies (URMAN), Institut Sup´ erieur des Sciences Appliqu´ ees et de Technologie de Kasserine, Universit´ e de Kairouan, BP 471, Kasserine 1200, Tunisia d Laboratoire de Physique des Mat´ eriaux et des Nanomat´ eriaux appliqu´ ee ` a l’Environnement, Universit´ e de Gab` es, Facult´ e des Sciences, Cit´ e Erriadh, Zrig, 6072 Gab` es, Tunisia e Department of Environmental Sciences, Faculty of Meteorology, Environment and Arid Land Agriculture, King Abdulaziz University, Jeddah, Saudi Arabia A R T I C L E INFO Keywords: Electrical analysis Unsubstituted PdPc Impedance spectroscopy Pellet form Absorbance ABSTRACT A pressed pellet of unsubstituted palladium (II) phthalocyanine (PdPc) was synthesized and characterized by UV- Vis transmittance and impedance spectroscopy. Optical absorbance analysis revealed that upon increasing the concentration, the absorption at 630 nm became more intense, demonstrating strong aggregation at high con- centrations. For the synthesized PdPc pellet, the absorbance decreased beyond 800 nm, and the direct band gap energy was 1.95 eV. The electric properties of the sample were studied for a range of frequency (40–10 7 Hz) and temperature (300–660 K) using complex impedance analysis. The activation energy and the relaxation time values for both time and frequency ranges were close to each other, suggesting that the electrical conduction and relaxation phenomena were controlled by the same type of charge carrier in the sample. Notably, the sample exhibited a semiconductor–metal transition at temperature T SM = 560 K. The AC-conductance was satisfactorily explained using the Jonscher universal power law. The electrical transport mechanism was dominated by the overlapping large polaron tunneling (OLPT) model. Furthermore, impedance spectroscopy analysis revealed a non-Debye-type relaxation. The Nyquist plot indicates the presence of grains and grain boundary effects. The results demonstrate that this material may be a promising candidate for photovoltaic applications. 1. Introduction The family of aromatic macrocycles that have a delocalized 18-π electron system forms phthalocyanine (Pc) compounds, which can act as effective functional materials because of their remarkable physical properties and stability [1]. These special characteristics have encour- aged their applications in various technological and scientifc domains, such as chemical sensors [2,3], catalysis [4], liquid crystals [5], solar energy conversion [6], semiconductors [7], optical data storage [8], dye-sensitized solar cells [9,10], and supercapacitors [11]. Phthalocy- anines (Pcs) are also characterized by their electron delocalization, high symmetry, planarity, and thermal stability [12,13]. Currently, metal phthalocyanines (MPcs) have generated consider- able interest in various domains because of their unique performance and properties [14]. Among MPcs, palladium (II) phthalocyanine (PdPc) is a divalent metal characterized by its greater exciton diffusion length than that of CuPc and ZnPc, respectively [15], making it a promising compound for various devices, especially photovoltaic [16–18]. Therefore, enhancing the electrical conductivity of Pcs by utilizing the complexity of bivalent metal ions is an important procedure. Accordingly, signifcant interest has been devoted to studying the opti- cal and electrical properties of Pc compounds and derivatives thereof. This is because the processes of dielectric relaxation and electrical conductivity of these compounds are crucial for their effective usage. Some of the dielectric properties of PdPcs have been reported [19,20]. Notably, studying dielectric relaxation is signifcant for analyzing the dielectric losses, determination of defects, and structure in solids [21]. The electrochemical characterization of certain PdPcs was reported in * Corresponding author at: Department of Physics, Faculty of Applied Science, Umm AL-Qura University, P. O. Box 715, Makkah, Saudi Arabia. E-mail addresses: timoumiabdelmajid@yahoo.fr, aotemoume@uqu.edu.sa (A. Timoumi). Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.elsevier.com/locate/synmet https://doi.org/10.1016/j.synthmet.2020.116659 Received 9 August 2020; Received in revised form 29 October 2020; Accepted 29 November 2020