Optical characterization of organic material bromoindium phthalocyanine thin films grown by electron beam evaporation Salar Pourteimoor • M. E. Azim Araghi • Sobhenaz Riyazi • Ali Askari Received: 24 February 2014 / Accepted: 13 March 2014 / Published online: 22 March 2014 Ó Springer Science+Business Media New York 2014 Abstract This paper presents the optical properties of organic material bromoindium phthalocyanine (BrInPc) thin films grown by electron beam evaporation technique. The paper describes the optical characteristics of BrInPc thin films, which have been determined using spectropho- tometric measurements of the absorbance, transmittance and reflectance at normal incident of light in the spectral range 300–1,100 nm. The optical band gap energy and type of the electronic transition have been determined by ana- lysis of spectral behavior of absorption coefficient, which reveals the probability of both direct and indirect transi- tions. Other optical constants, such as refractive index, extinction coefficient, complex dielectric constant and optical conductivity of thin films have been evaluated. Moreover, the width of band tails of localized states (Ur- bach energy), steepness parameter and width of the defect states have been determined by studying the absorption coefficient spectra just below the fundamental absorption edge. 1 Introduction In recent years, organic molecular materials that are com- posed of p-conjugated molecules are intensively investi- gated in regard to their wide range of applications in opto and microelectronics. Among these materials, phthalocyanines thin films, due to their low cost and interesting optical properties like photovoltaic [1], elec- trochromic [2] or even optical nonlinear behavior (optical limiting) [3], are widely used to build high quality elec- tronic devices [4–6]. The accurate determination of the optical properties of these materials is important, not only in order to know the basic mechanisms underlying these phenomena, but also to exploit and develop their interest- ing technological applications. It is well known that Metal-phthalocyanines (MPc’s) are semiconductor and have p-electron system [7]. The con- jugated p system of MPc leads to intense electronic absorption bands in the UV–Visible region (intense absorption in the red and blue spectrum range, which makes them very pure blue pigments) [8]. Because of the excellent resistance in chemical degradation, ease of syn- thetic modification, high thermal stability and low subli- mation temperature, the molecules of MPc can be sublimed as thin films with high quality without dissociation. If MPc’s are evaporated onto substrates at room temperature, the a-form will normally be obtained. Moreover, it was reported that a-form can be converted into b-form by successive sublimation [9], annealing or depositions at higher substrate temperatures [10]. Moreover, the optical properties of a functional organic material with a p-con- jugated system depend strongly the deposition method, substrate identity, substrate temperature during deposition, post-deposition annealing, the film thickness and rate of deposition [11]. Optical studies of phthalocyanines in condensed media are of special significance because of the effectiveness of these systems as potential candidates in a variety of tech- nological applications. The optical constants of thin films provide us with information concerning microscopic characteristics of the material and its determination is very S. Pourteimoor (&)  M. E. Azim Araghi  S. Riyazi Applied Physics Division, Physics Department, Kharazmi University, 43 Mofateh Avenue, Tehran, Iran e-mail: salar.tmu@gmail.com S. Pourteimoor  A. Askari Physics Department, Shahrood University of Technology, Shahrood, Iran 123 J Mater Sci: Mater Electron (2014) 25:2325–2332 DOI 10.1007/s10854-014-1879-1