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Organic Small-Molecule Materials for Organic Light-Emitting Diodes
Published in Zhigang Rick Li, Organic Light-Emitting Materials and Devices, 2017
Shijian Su, Norman Herron, Hong Meng
A highly efficient and chromatically stable WOLED based on an anthracene derivative blue emitter doped with yellow–orange 5,6,11,12-tetraphenylnaphthacene (rubrene) was reported by Qiu’s group [572]. By simple deposition of the mixture of the predoped rubrene and two anthracene derivatives in the host material NPD, a maximum brightness of 20,100 cd/m2 with a peak EQE of 2.4% (5.6 cd/A) at 9 V and luminance-independent CIE coordinates of (0.32, 0.34) has been achieved in an OLED with the device structure of ITO/NPD/ADN:2.5% TBADN:0.025% rubrene/Alq3/Mg:Ag. The results also indicate that using two anthracene derivatives improves the morphology of the doped films and depresses the crystallization of the dopant, which in turn contributes to the high performance and stability of the device. This strategy has also been applied to achieve a high-efficiency blue OLED by the same group.
Organic Semiconducting Single Crystals as Novel Room-Temperature, Low-Cost Solid-State Direct X-Ray Detectors
Published in Salah Awadalla, Krzysztof Iniewski, Solid-State Radiation Detectors, 2017
It is important here to remember how the use of single crystals has been fundamental to the development of semiconductor microelectronics and solid-state science. Whether based on inorganic [23,24] or organic [25,26] materials, the devices that show the highest performance rely on single-crystal interfaces, due to their nearly perfect translational symmetry and exceptionally high chemical purity. Moreover, organic single crystals show band-like transport behavior [27], and top-performing rubrene single crystals (vapor grown, only a few microns thick) have been recently reported to reach hole mobilities of 40 cm2 V-1 s-1 [28] and electron mobilities up to 11 cm2 V-1 s-1, measured in a field-effect transistor configuration, which allows the current flowing through the crystal to be controlled and amplified [29–32]. The same crystals, when sufficiently thin (i.e., less than 3 μm), are reportedly conformable/flexible [33].
Correcting π-delocalisation errors in conformational energies using density-corrected DFT, with application to crystal polymorphs
Published in Molecular Physics, 2023
Bhaskar Rana, Gregory J. O. Beran, John M. Herbert
Dispersion-corrected density functional theory (DFT+D) had made enormous strides towards making crystal structures predictable from first principles [22,29–34], but this success is mitigated in certain cases by overstabilisation of delocalised π-electron systems [26,28,35,36], which is a consequence of self-interaction error (SIE) [37]. This issue is thought to impact polymorph prediction in well-known examples such as the anti-cancer drug axitinib [26], the organic semiconductor molecule rubrene [38], the well-studied ROY molecule [26,28,35,39,40], molecule X [26,41] from the third blind test of crystal structure prediction [42], as well as other systems [26,36,43]. Structures for several of these molecules are shown in Figure 1. Each of these molecules exhibits conformational polymorphism whereby changes in intramolecular conformation access different intermolecular crystal packing motifs. Notably, in each of these molecules, the extent of π-electron delocalisation changes as a function of one or more intramolecular torsional coordinates. To the extent that delocalisation error may overstabilise the more highly-conjugated conformations, we expect that DFT will produce erroneous conformational energy profiles for these flexible monomers. Those errors propagate into errors in the relative energies for the crystal polymorphs formed from these monomers [26,28,35,39]. Given the small energy differences between polymorphs, even modest conformational energy errors can have a qualitative impact on polymorph stability ordering.