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Effect of Solvents, Their Mixture and Thermal Annealing on the Performance of Solution Processed Polymer Light-Emitting Diodes
Nanoelectronics Research Group, Academic Center for Education, Culture and Research (ACECR), Khajeh Nasir Toosi University of Technology, Tehran 15569-14846, Iran
Institute for Experimental Physics, Ulm University, Ulm D-89081, Germany
Faculty of New Sciences and Technologies, University of Tehran, Tehran 14395-1374, Iran
* Author to whom correspondence should be addressed.
Received: 11 February 2013; in revised form: 29 March 2013 / Accepted: 3 May 2013 / Published: 15 May 2013
Abstract: In this study, we first investigated changes seen in electrical and optical properties of a polymer light-emitting diode due to using different kinds of solvents and their mixture. Two-layer light emitting diodes with organic small molecules doped in a PVK polymer host were fabricated using (i) non-aromatic solvent chloroform with a high evaporation rate; (ii) aromatic solvent chlorobenzene with a low evaporation rate, and (iii) their mixture with different relative ratios. The effect of nano-scale layer thickness, surface roughness and internal nano-morphology on threshold voltage and the amount of electric current, the luminance and efficiency of a device were assessed. Results indicated the importance of majority charge carriers’ type in the selection of solvent and tuning its properties. Then, the effect of thermal annealing on electrical and optical properties of polymer light emitting diodes was investigated. During the device fabrication, pre-annealing in 80 and/or 120 °C and post-annealing in 120 °C were performed. The nano-scale effect of annealing on polymer-metal interface and electric current injection was described thoroughly. A comparison between threshold voltage, luminance and electric current efficiency of luminescence for different annealing processes was undertaken, so that the best electric current efficiency of luminescence achieved at 120 °C pre-annealing accompanied with 120 °C post-annealing.
Keywords: aromatic solvent; post-thermal annealing; pre-thermal annealing; polymer light emitting diode; interface; semiconductor polymer; solvent mixture
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Rezvani, M.H.; Farajollahi, F.; Nikfarjam, A.; Bakhtiarpour, P.; Saydanzad, E. Effect of Solvents, Their Mixture and Thermal Annealing on the Performance of Solution Processed Polymer Light-Emitting Diodes. Materials 2013, 6, 1994-2006.
Rezvani MH, Farajollahi F, Nikfarjam A, Bakhtiarpour P, Saydanzad E. Effect of Solvents, Their Mixture and Thermal Annealing on the Performance of Solution Processed Polymer Light-Emitting Diodes. Materials. 2013; 6(5):1994-2006.
Rezvani, Mohammad H.; Farajollahi, Farid; Nikfarjam, Alireza; Bakhtiarpour, Parisa; Saydanzad, Erfan. 2013. "Effect of Solvents, Their Mixture and Thermal Annealing on the Performance of Solution Processed Polymer Light-Emitting Diodes." Materials 6, no. 5: 1994-2006.