In silico studies of OLED device architectures regarding their efficiency

Simulations have become increasingly important to understand and design organic optoelectronic devices, such as organic light emitting diodes (OLEDs) and to optimize their performance by selecting appropriate materials and layer arrangements. To achieve accurate device simulations, it is crucial to consider the interplay between material properties, device architecture, and operating conditions and to incorporate physical processes such as charge injection, transport, recombination, and exciton decay. Simulations can provide insights into device bottlenecks and streamline optimization cycles, eliminating the need for physical prototyping and rationalizing OLED design. In this study, we investigated three heuristic OLED architectures with a 3D kinetic Monte Carlo (kMC) model and compared their quantum efficiency at different operation voltages. Our investigation focused on examining the effects of various layer arrangements on charge and exciton dynamics in OLED devices and establishing design principles for achieving high efficiency, which are consistent with experimental observations. Notably, we find that increasing the thickness of the emissive layer (EML) led to higher luminance efficiency, and that an emitter concentration of approximately 5% results in optimal performance. By using this model, it is possible to rapidly study the influence of many device parameters and explore a broad range of parameter and architecture space within a reasonable time-frame

Systematic kMC Study of Doped Hole Injection Layers in Organic Electronics

Organic light emitting diodes (OLED) play an important role in commercial displays and are promising candidates for energy-efficient lighting applications. Although they have been continuously developed since their discovery in 1987, some unresolved challenges remain. The performance of OLEDs is determined by a multifaceted interplay of materials and device architectures. A commonly used technique to overcome the charge injection barrier from the electrodes to the organic layers, are doped injection layers. The optimization of doped injection layers is critical for high-efficiency OLED devices, but has been driven mainly by chemical intuition and experimental experience, slowing down the progress in this field. Therefore, computer-aided methods for material and device modeling are promising tools to accelerate the device development process. In this work, we studied the effect of doped hole injection layers on the injection barrier in dependence on material and layer properties by using a parametric kinetic Monte Carlo model. We were able to quantitatively elucidate the influence of doping concentration, material properties, and layer thickness on the injection barrier and device conductivity, leading to the conclusion that our kMC model is suitable for virtual device design

6. - 8. Sınıf Öğrencilerinin Fiziksel Aktiviteye Katılımında Algıladıkları Sosyal Desteğin Rolü

The purpose of this study was to investigate the role of perceived social support on 6th, 7th and 8th grade students’ physical activity levels with regard to gender and school type (private versus public). In this study, both qualitative and quantitative research methodologies were applied. The participants were 266 students from one public and one private school. It is found that perceived social support seems to be an important factor on students’ physical activity patterns. Participants reported that they received more social support from their peers when compared to their parents, wherein their mothers were the only significant social support provider. Results also revealed that students from the private school significantly received more social support from their family compared to students from the public school. Moreover, physically active students, especially girls, reported that they received more social support from their mothers.Bu çalışmanın amacı, 6., 7. ve 8. sınıfta öğrenim gören öğrencilerin fiziksel aktivite düzeylerine göre algıladıkları sosyal destek sağlayıcıları ve türlerini, farklı okul türü (özeldevlet) ve cinsiyetleri açısından nicel ve nitel araştırma yöntemlerini kullanarak incelemektir. Araştırmanın örneklemini bir devlet okulu ve bir özel okulda öğrenim gören 266 altıncn, 7. ve 8. sınıf öğrencisi oluşturmaktadır. Araştırma sonuçları, sosyal desteğin bireylerin fiziksel aktiviteye katılımında önemli bir etken olabileceğini göstermektedir. Bu yaş grubundaki bireylerin, ailelerine oranla arkadaşlarından daha çok destek aldıkları; fakat aileden, özellikle de anneden algılanan sosyal desteğin fiziksel aktiviteye birlikte katılım, fiziksel aktiviteye teşvik etme ve aktivitenin türünü seçmede belirleyici bir rol oynadığı görülmektedir. Özel okuldaki katılımcıların devlet okulundaki katılımcılara oranla fiziksel aktiviteye katılımda ailelerinden algıladıkları sosyal desteğin anlamlı olarak daha yüksek olduğu görülmüştür. Bununla birlikte, fiziksel aktivite düzeyi yüksek olan özellikle de kız öğrencilerin, annelerinden algıladıkları sosyal desteğin fiziksel aktiviteye katılımda anlamlı olarak farklılaştığı görülmektedir

Understanding excited state properties of host materials in OLEDs: simulation of absorption spectrum of amorphous 4,4-bis(carbazol-9-yl)-2,2-biphenyl (CBP)

4,4-Bis(carbazol-9-yl)-2,2-biphenyl (CBP) is widely used as a host material in phosphorescent organic light-emitting diodes (PhOLEDs). In the present study, we simulate the absorption spectra of CBP in gas and condensed phases, respectively, using the efficient time-dependent long-range corrected tight-binding density functional theory (TD-LC-DFTB). The accuracy of the condensed-phase absorption spectra computed using the structures obtained from classical molecular dynamics (MD) and quantum mechanical/molecular mechanical (QM/MM) simulations is examined by comparison with the experimental absorption spectrum. It is found that the TD-LC-DFTB gas-phase spectrum is in good agreement with the GW-BSE spectrum, indicating TD-LC-DFTB is an accurate and robust method in calculating the excitation energies of CBP. For the condensed-phase spectrum, we find that the electrostatic embedding has a minor influence on the excitation energy. Computing accurate absorption spectra is a particular challenge since static and dynamic disorders have to be taken into account. The static disorder results from the molecular packing in the material, which leads to molecule deformations. Since these structural changes sensitively impact the excitation energies of the individual molecules, a proper representation of this static disorder indicates that a reasonable structural model of the material has been generated. The good agreement between computed and experimental absorption spectra is therefore an indicator for the structural model developed. Concerning dynamic disorder, we find that molecular changes occur on long timescales in the ns-regime, which requires the use of fast computation approaches to reach convergence. The structural models derived in this work are the basis for future studies of charge and exciton transfer in CBP and related materials, also concerning the degradation mechanisms of CBP-based PhOLEDs

Anne sütüyle beslenen yenidoǧanlarda hipernatremik dehidratasyon

Introduction: Since it can cause life-threatening complications in newborns, diagnosis and treatment of hypernatremic dehydration associated with inadequate breastfeeding is important. Materials and Methods: Records of exclusively-breastfed newborns (37-42 weeks) with hypernatremic dehydration (serum Na ≥ 150mEq/L) admitted between 2006 and 2012 were reviewed retrospectively. Results: The mean gestational age, birth weight, weight loss, maternal age, and age at diagnosis of 26 newborns with hypernatremic dehydration were 38.8±1.1 weeks, 3292±458 gr, 13.5±5.5%, 27.6±4.9 years, and 3.9±3.5 days, respectively. The percentages of female patients, caesarean delivery, and primipar mothers were 57.6%, 61.6%, and 57.6% respectively. Admission complaints were fever (30.7%), poor feeding and jaundice (26.9%), restlessness and hypoactivity (7.6%). Hypernatremic dehydration frequency within first five days, in summer season, during hospitalization were 84.6%, 73%, and 42.3%, respectively. The mean serum BUN, creatinine, Na levels were found 45.6±64.1 mg/dl, 1.5±2.3 mg/dl, and 157±11.9 mEq/L, respectively. Of 26 mothers, 57.6% had received breastfeeding education and 84% had inadequate fluid intake. Among four patients with seizures, three had prerenal failure, one had renal failure requiring dialysis, and brain edema developed in one. Serum Na levels were higher in infants who were baby of primipar mother (p=0.002), born in another hospital (p=0.012), from young mothers (p=0.035), from mothers with no breastfeeding education (p=0.007), and with delayed hospital admission (p<0.01). Serum Na concentrations ≥160mEq/L were associated with complications (p<0.01). Serum Na levels were negatively correlated with maternal age (p=0.035) and positively correlated with (p=0.016) weight loss. Conclusions: Hypernatremic dehydration can be prevented in newborns by close monitoring of weight loss and by teaching successful breastfeeding techniques and signs of dehydration to the mothers within first week. © The Journal of Current Pediatrics, published by Galenos Publishing