Handheld and automated ultrasonic spray deposition of conductive PEDOT:PSS films and their application in AC EL devices

In this contribution we explore the spray deposition technique to achieve smooth films based on the conductive polymer PEDOT:PSS. Two different spray systems were used and compared namely: (a) handheld airbrush and (b) automated ultrasonic spray system. For each system a number of parameters were pre-adjusted during coating control experiments such as spray head distance, angle and cone for airbrush as well as flow rate, power and focus for ultrasonic nozzle. Water-based solutions of PEDOT:PSS having 20% of N-methylpyrrolidone (NMP) were sprayed on glass substrates at temperatures ranging from 75 to 150 degrees C. The resulting films were further chemically treated with ethylene glycol (EG) and evaluated with respect to their morphological, electrical and optical properties. Before EG-treatment the ultrasonic spraying resulted in smoother films with conductivity up to 2-3.9 times higher than their airbrushed counterparts. Deposition temperature proved to have minor effect on the morphological and electro-optical properties of PEDOT:PSS films. On the other hand, the film conductivity was enhanced, peaking at 610.1 S cm (1) for ultrasonic spraying, when further chemically modified by EG. IR microspectroscopy mapping analysis, Raman spectroscopy and XRD data indicated a phase-separation between PEDOT and PSS chains and increasing crystallinity in the ultrasonically sprayed films. The application of such PEDOT:PSS films as transparent electrode in flexible AC EL devices is demonstrated. (C) 2014 Elsevier B.V. All rights reserved.