Rubrene characteristics

The main features of the chemiluminescence mechanism are exemplarily illustrated in Scheme 11 for the reaction of bis(2,4,6-trichlorophenyl)oxalate (TCPO) with hydrogen peroxide in the presence of imidazole (IMI-H) as base catalyst and the chemiluminescent activators (ACT) anthracene, 9,10-diphenylanthracene, 2,5-diphenyloxazole, perylene and rubrene. In this mechanism, the replacement of the phenolic substituents in TCPO by IMI-H constitutes the slow step, whereas the nucleophilic attack of hydrogen peroxide on the intermediary l,l -oxalyl diimidazole (ODI) is fast. This rate difference is manifested by a two-exponential behavior of the chemiluminescence kinetics. The observed dependence of the chemiexcitation yield on the electrochemical characteristics of the activator has been rationalized in terms of the intermolecular CIEEL mechanism (Scheme 12), in which the free-energy balance for the electron back-transfer (BET) determines whether the singlet-excited activator, the species responsible for the light emission, is formed ... 

Figure 149 PL and EL spectra of the multi-layer structure shown in the inset. The principal maximum is characteristic of rubrene (Rb) doped in the thin (3nm) layer of Alq3 [10% Rb Alq3], Adapted from Ref. 565.

OFETs with parylene dielectric are very stable. For example, the characteristics of rubrene/parylene transistors remained unchanged after storing the devices for more than two years in air and in the dark. 

Figure 2.1.10 shows the transconductance characteristics (i.e., the dependence of the source-drain current on the gate voltage, 4j,( E ), measured at a constant source-drain voltage, E50) and /sd(V sd) characteristics typical for the p-type rubrene singlecrystal OFETs [29,30,39], The channel conductance per square. 

FIGURE 2.1.10 The transconductance IsoiV ) (the upper panel) and /sd( sd) (the lower panel) characteristics of rubrene single-crystal OFET (see, for example, Podzorov et al. [30] and Menard et al. [39]). 

A density-independent ft has been observed in devices based on single crystals of rubrene [30,35,36], pentacene [33,34], tetracene [31], and TCNQ [39]. This important characteristic of single-crystal OFETs contrasts sharply with a strongly Vg-dependent mobility observed in organic TFTs [64] and a-Si H FETs [65]. In the latter case, the density of localized states within the gap is so high that the Fermi level remains in the gap even at high jl/gl values. 

Single-crystal OFETs provide a unique tool for the express analysis of transport characteristics of new molecular materials with defect densities much smaller than those in TFTs. Therefore, even though large-scale applications will ultimately rely on thin films, research on single-crystal OFETs can play an important role in the material selection for applied devices. The case of rubrene perfectly illustrates this point. The unprecedented quality of OFETs based on vapor-grown rubrene crystals has stimulated work on the deposition of rubrene thin-films from solution Stingelin-Stutzmann et al. have recently demonstrated solution-processed rubrene TFTs with high mobility (up to 0.7 cmWs at room temperature) [111]. 

The simulated current-voltage characteristic (Fig. 8.30) corresponds roughly to the experimentally-determined characteristics for rubrene and tetracene crystals in the non-ohmic range (Fig. 8.27). For the ultrapure tetracene crystals, the values fx 1 cm /Vs for the mobility at room temperature and Nt<5-10 cm , Et 700 meV for the density and the depth of the charge-carrier traps were found [37]. 

First, OLEDs fabricated by vacuum process are discussed. Four kinds of OLEDs fabricated by OMBD are discussed and the emission characteristics are summarized. There are two types of organic materials for OLEDs one for undoped type such as a-NPD and Alqg, and the other is for doped type such as rubrene and porphine derivative (TPP), which are doped in a carrier transporting material. In case of a device in which a-NPD is... 

Emission characteristics of OLED with rubrene doped in Alqj emissive layer, (a) Emission spectrum and the molecular structure of rubrene. (From Ohmori, Y. et al., IEEE J. Selected Top. Quantum Electron., 10, 70,2004. With permission.) (b) Current-voltage and EL intensity-voltage characteristics of OLEDs, and (c) EL output signal at lOOMHz directly modulated by pulsed voltage application. (From Ohmori, Y. et al., IEEE. Selected Top. Quantum Electron., 10, 70, 2004. With permission.)... 

The high quality of rubrene crystals has allowed detailed measurements of the transport characteristics, including the recent observation of the Hall effect [26]. Charge transport in rubrene single crystals, while trap-limited at low temperature, appears to occur via delocalized states over the 150-300 K temperature range with an (anisotropic) hole mobility of up to 20 cm /V s at room temperature [27,28]. 

In order to investigate the referenced inkjet-printed film in an OLED, some inkjetted PEDOT-PSS films were used as the anode. On top of the inkjet-printed anode, the hole transport layer (HTL) solution (TPD, [M, M, -bis(3-methylphenyl)-N JV dimethyl benzidine] 67.6 wt.%, polycarbonate (PC) 29.0 wt.%, rubrene 3.4 wt.%, 10.35 mg/ml chloroform) was spin-coated at 1000 rpm for 1 min in a class 100 cleanroom. A 60 nm layer of tris-(8-hydroxyquinoline)-aluminum (Alq3) was then thermally deposited under the high vacuum at the rate of 0.7 A/s. Then, a 300 nm layer of Mg Ag (magnesium -silver) was thermally coevaporated at the ratio of 10 1 on the top of electron transport layer (ETL) layer (Figure 3.10). The thickness of spin-coated layers was matched to one of the inkjet-printed layers (L = 0). Additionally, Figure 3.10 shows results of OLED characteristics with the same layer configuration except that ITO is used as the anode layer. 

Dufraisse, C. and Horclois, R., Synthesis of naphthacenes with the characteristics of rubrenes. Bull. 

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