Organometallic Coatings for Electroluminescence Applications

Abstract

Organometallic compounds embedded in thin films are widely used for Organic Light-Emitting Diodes (OLED), but their functionalities are strongly correlated with the intrinsic properties of those films. Controlling the concentration of the organometallics in the active layers influences the OLED performances through the aggregation processes. These aggregations could lead to crystallization processes that significantly modify the efficiency of light emission in the case of electroluminescent devices. For functional devices with organometallic-based thin films, some improvements, such as the optimization of the charge injection, are needed to increase the light output. One dual emitter IrQ(ppy)2 organometallic compound was chosen for the aggregation correlations from a multitude of macromolecular organometallics that exist on the market for OLED applications. The choice of additional layers like conductive polymers or small molecules as host for the active layer may significantly influence the performances of the OLED based on the IrQ(ppy)2 organometallic compound. The use of the CBP small molecule layer may lead to an increase in the electroluminescence versus the applied voltage.

Detailed Molecular and Structural Analysis of Dual Emitter IrQ(ppy)2 Complex

“…The signals in the 1D NMR spectra showed the expected number of protons: 22 protons (eight ppy H resonances twice and six quinoline H resonances). The proton signals were assigned to their position in the bicycling system of the ligand by COSY, HMBC, HSQC, TOCSY and NOESY and In the powder form, a π-π stacking process between the adjacent IrQ(ppy) 2 takes place and distances between quinoline ligands compete with the intermolecular interactions [18,47] which induces inter-ligand energy transfer (ILET) [48]. The emission processes follow the excitation in the 1 MLCT state and an efficient transfer to the 3 MLCT due to the strong spin-orbit coupling.…”

“…In the powder form, a π-π stacking process between the adjacent IrQ(ppy)2 takes place and distances between quinoline ligands compete with the intermolecular interactions [18,47] which induces inter-ligand energy transfer (ILET) [48]. The emission processes follow the excitation in the 1 MLCT state and an efficient transfer to the 3 MLCT due to the strong spin-orbit coupling.…”

“…The use of organometallic compounds in new technologies such as organic light-emitting diodes (OLED) [1][2][3][4][5][6][7][8], photovoltaic applications [9] or catalysis [10], requires different approaches during the chemical synthesis of these compounds, going from the photoluminescence, electroluminescence and internal quantum efficiency to the charge transport and the amorphous-crystalline interplay between these organometallic molecules [11][12][13][14][15][16][17][18].…”

Photophysical and Electro-Optical Properties of Copolymers Bearing Blue and Red Chromophores for Single-Layer White OLEDs

“…Further analysis of the J-V characteristics enables the evaluation of the carrier mobility in the respective devices. In general, J and V relationship in a semiconducting layer is expressed by J ∝ V m and has been known to be composed of several distinctive regions, which are defined by the value of exponent m. More specifically, these regions include: (a) the low-voltage zone, that corresponds to ohmic conduction across the sandwich structure Ohmic current, where J is linearly proportional to V (J ∝ V), (b) the Trap-limited Space Charge Limited Current (T-SCLC) zone, where the exponent is around 1-2 (J ∝ V 1-2 ), (c) the Trap-Filled Limited (TFL) current zone, being characteristic of amorphous materials, in which induced traps are filled with charges and the exponent is between 2 and 100 (J ∝ V 2-100 ) and finally (d) the Space Charge Limited Current (SCLC) zone, which is the high-voltage zone where the exponent is close to 2 (J ∝ V 2 ) and it is dominated by the trap filling process since the increase of current causes a gradual filling of the states [43][44][45][46][47][48][49][50]. In our results, we cannot distinguish the Ohmic and T-SCLC regions.…”

“…Especially, in the case of CzHom and CzCop devices, the slope of TFL zone (3-6 V) is ~7.32 and ~8.44, respectively, whereas in the case of the WCop1 and Wcop2 devices (1-8 V) it is ~2.87 and ~3.41, respectively. The difference in the voltage range of the TFL zone between the devices is related to their different turn-on voltage (4 V for CzHom and CzCop to 2 V for Wcop1 and Wcop2) due to the higher activation energy [43][44][45].…”