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.
Highlights
Semiconductor polymers and organic materials have been increasingly used in electrical and optical devices [1,2,3,4,5]
In polymer light emitting diodes (PLED), different factors, e.g., type of solvent, spinning speed and substrate material affect the performance of the device [16,17,18]
H holes are inj njected from m the indium tin oxide (ITO) electrode e innto the PED
Summary
Semiconductor polymers and organic materials have been increasingly used in electrical and optical devices [1,2,3,4,5]. The properties of a solvent have a critical role in the performance of devices fabricated through the spin coating method [11,13,14,15] Tuning these properties could be an effective route for changing the behavior and improving the electrical and optical performance of the devices. In polymer light emitting diodes (PLED), different factors, e.g., type of solvent, spinning speed and substrate material affect the performance of the device [16,17,18]. The effect of thermal annealing in different steps of the fabrication process on the electrical and optical properties of the device and its underlying mechanism is investigated. The optimized parameters and conditions for device performance are concluded
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