Abstract
Light emission properties of a fluorene cross-conjugated polymer (PF–1) based on the monomer 4,7-bis[2-(9,9-dimethyl)fluorenyl] benzo[1,2,5]thiadiazole are reported. This polymer exhibits solubility at high concentrations, good processability into thin solid films of good quality and a broad emission band with a fluorescence quantum yield of approximately 1. Based on these features, in this paper we implemented the use of PF–1 as an active layer in polymer light-emitting diodes (PLEDs) and as a laser gain medium in solution. To get insight on the conducting properties of PF–1, two different electron injectors, poly [(9,9-bis(3′-(N,N-dimethylamino) propyl)-2,7-fluorene)-alt-2,7-(9,9–dioctylfluorene)] (PFN) and lithium fluoride (LiF), were used in a simple PLED architecture. PLEDs with the PFN film were found to exhibit better performance with a maximum luminous efficiency of 40 cd/A, a turn-on voltage (Von) of approximately 4.5 V and a luminance maximum of 878 cd/m2 at 5.5 V, with a current density of 20 A/m2. For the lasing properties of PF–1, we found a lasing threshold of around 75 μJ and a tunability of 20 nm. These values are comparable with those of rhodamine 6G, a well-known laser dye.
Highlights
Since the first report of electroluminescence in conjugated polymers in 1990 [1], numerous materials of this kind have been designed and synthesized to be used as active compounds for polymer light-emitting diodes (PLEDs)
PLEDs were fabricated using an Indium Tin Oxide (ITO)-covered glass substrate ultrasonically cleaned for 30 min in each of the following baths: distilled water, ethanol and an alkaline solution (Hellmanex II mixed with water)
PLEDs fabricated with current density are shown in Figure 5a,b, respectively
Summary
Since the first report of electroluminescence in conjugated polymers in 1990 [1], numerous materials of this kind have been designed and synthesized to be used as active compounds for polymer light-emitting diodes (PLEDs). Polymers 2016, 8, 43 electro-luminance devices are to improve the manufacturing process including deposition methods, and theimprove design of chemical structures with highdeposition fluorescence quantum yield are to thenovel manufacturing process including methods, and the which designincreases of novel the emission spectrum characteristics [6,7,8,9].increases. The use the of emission highly fluorescent chemical structures withand highcurrent-voltage fluorescence quantum yield which spectrum materials, such as characteristics oligomers and[6,7,8,9]. Among the wide variety of materials used for PLEDs, fluorene-based polymers and polymers, opens the possibility of improving the PLEDs’ performance [8,10]. Among the wide show and unique chemical and physical polymers propertiesshow suchinteresting as a rigid planar biphenyl unit, varietyinteresting of materials used for PLEDs, fluorene-based and unique chemical which improves solubility, as well as thermal stability and processability [10,11,12]; they comprise and physical properties such as a rigid planar biphenyl unit, which improves solubility, as well as aromatic segments which help to reduce the turn-on voltagearomatic (Von) thatsegments results from a good in thermal stability and processability they comprise which helpbalance to reduce electron and hole injection [13,14]
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