Effect of Annealing Induced Morphology on Mobility of Copper Phthalocyanine Thin Films
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Effect of Annealing Induced Morphology on Mobility of Copper Phthalocyanine Thin Films Rosemary Davis1 · Avinash Nelson Asokan2 · P. Predeep1 Received: 12 March 2020 / Accepted: 12 May 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Post deposition annealing of copper phthalocyanine (CuPc) films develops nano-rod structures on the surface of the film and the length and uniformity of nano-rods depend on the annealing temperature. The proposed methodology combines scanning electron microscopy (SEM) and atomic force microscopy (AFM) with impedance spectroscopy to give new insights into the influence of thermally developed nano structures on the charge carrier mobility of CuPc films. The impedance spectroscopy provides a non-invasive and cost-effective study which finds that the hole mobility of CuPc films improves upon increasing annealing temperature, reaches maximum of (5.3 ± 0.7) × 10–5 cm2V−1 s−1 at 150 °C and reduces at higher temperatures. These results will benefit future strategies for the surface modification of small molecular films for improved charge transport in organic and hybrid devices. Keywords Organic electronics · Impedance spectroscopy · Copper phthalocyanine (CuPc) · Charge carrier mobility · Nanorod structure
1 Introduction The field of organic electronics is rapidly expanding due to their flexibility, ease of fabrication, lightness and surpassing performance in every year [1, 2]. Active materials in organic electronics fall into two categories; polymers and small molecules. In comparison with polymer films, small molecule films exhibits higher purity and reproducibility [3] because they are mainly processed through vacuum techniques while polymers are solution processed. Different from solutionprocessing, vacuum deposition allows control over the thickness and enables very thin and uniform film formation [4]. Small molecular films find a vast range of applications including organic and perovskite solar cells [5, 6], organic light-emitting diodes (OLED) [7] and organic field-effect transistors (OFET) [8, 9]. The mobility of charge carriers is a crucial factor deciding the performance of an organic electronic device. It has * P. Predeep [email protected] 1
LAMP, Department of Physics, National Institute of Technology, Calicut, India
Department of Electrical Engineering, National Institute of Technology, Calicut, India
2
a prime role in deciding exciton dissociation [10] and short circuit current [11] in solar cells, luminescent efficiency in LEDs [12] and transistor action in organic transistors [9]. Lower mobility of organic semiconducting materials in comparison with the inorganic materials becomes the chief cause of inferior performance of organic electronics. It is reported that proper alignment and uniformity in organic semiconducting films enhance the mobility of charge carriers [13]. Applying electric field [13] or temperature [14],templating with suitable materials [15, 16] and solvent treatment [17] on the organic layer are used to obtain
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