Electrical, dielectric and electrochemical measurements of bulk aluminum phthalocyanine chloride (AlPcCl)

Highlights

• Study Ac conductivity and dielectric behavior of bulk material.

• Investigation of applied theoretical conduction mechanism.

• Calculation of density of states at certain conditions.

• Investigation dielectric properties through electric modulus.

• Determination frontier energy gap.

Abstract

AC conductivity and the related dielectric properties of bulk aluminum phthalocyanine chloride (AlPcCl) have been studied over a temperature range (303–403 K) and frequency range (42–10⁶ Hz). The universal power law ${\mathit{\sigma }}_{\mathrm{ac}}$(ω)=Aω^s has been used to investigate dependence of AC conductivity on frequency. The variation of the frequency exponent (s) with temperature was analyzed in terms of different conduction mechanisms; the predominant conduction mechanism was found to be the correlated barrier hopping (CBH) model. The barrier height was calculated by using (CBH) model, it was found to be 1.41 eV. Dependence of ${\mathit{\sigma }}_{\mathrm{ac}}$(ω) on temperature refers to a linear increase with increasing temperature at different frequencies. The density of states N ($E_{\mathrm{F}}$) was calculated to be equal 4.11×10¹⁹ cm⁻³ using Elliott model. It has been found that AC activation energy decreases with increasing frequency. Dielectric values were analyzed using complex permittivity and complex electric modulus for bulk AlPcCl at different temperatures. The obtained value of HOMO–LUMO energy gap was found to be 1.48 eV.

Introduction

Phthalocyanine and its derivatives play an essential role in various biological processes; both of them have unique chemical properties. These compounds play a key role in various industrial and biological processes. The interest in their properties is still attractive because of their potential applications as semiconducting devices such as: photovoltaic cells [1], laser printers [2], optical data storage systems [3], and light emitting diodes [4]. Phthalocyanines are conjugated aromatic compounds; where the molecule contains four isoindole rings. Many derivatives of phthalocyanines have been synthesized either by changing the central atom or adding some terminal function groups [5]. Among the various halogenated metal phthalocyanine, aluminum phthalocyanine chloride AlPcCl has received considerably less attention; although there is evidence that they exhibit properties suitable for gas sensing applications [6]. Metal Pc׳s characterized by their noteworthy morphological and thermal stability over a larger temperature range compared with unhalogenated Pc׳s [7].

The AC conductivity, ${\mathit{\sigma }}_{\mathrm{ac}}$, for most semiconductors shows a frequency dependence with ${\omega }^s$, where ω is the angular frequency [8]. Various models such as large polaron tunneling (LPT) model, atomic hopping model and correlated barrier hopping (CBH) model have been proposed to explain AC conduction mechanism for different materials [9]. Ac conductivity enables us to investigate internal time dependent processes with AC measurements.

Impedance spectroscopy plays an important role in solid state electronics field as it can resolve the conduction mechanism by differentiating among the transport properties of complex systems [10]. Dielectric relaxation studies enable us to understand the nature and the origin of dielectric losses, which could be useful in determination of defects and structure in solids. The magnitude of geometric and measured capacitance may differ if the electric field at the metal insulator interface varies with the insulator over the region. The objective of the present work is to study the dark alternating current AC conductivity and the related dielectric properties of bulk AlPcCl. Cyclic voltammetry of AlPcCl has been studied to determine band gap of the substance through electrochemical technique.