Routes for efficiency enhancement in fluorescent TADF exciplex host OLEDs gained from an electro‐optical device model

Fluorescence-based organic light-emitting diodes (OLEDs) using thermally activated delayed fluorescence (TADF) have increasingly attracted attention in research and industry. One method to implement TADF is based on an emitter layer composed of an exciplex host and a fluorescent dopant. Even though the experimental realization of this concept has demonstrated promising external quantum efficiencies, the full potential of this approach has not yet been assessed. To this end, a comprehensive electro-optical device model accounting for the full exciton dynamics including triplet harvesting and exciton quenching is presented. The model parameters are fitted to multiple output characteristics of an OLED comprising a TADF exciplex host with a fluorescent emitter, showing an external quantum efficiency of >10%. With the model at hand, an emission zone analysis and a parameter study are performed, and possible routes for further efficiency enhancement are presented

Dental age diagnostics by means of radiographical evaluation of the growth stages of lower wisdom teeth

The main criterion for dental age estimation in living adolescents and young adults is mineralization of third molars. A total of 1,260 orthopantomograms of 669 female and 591 male subjects aged between 15 and 22years was examined. Of the orthopantomograms, 1,137 were from patients with Swiss citizenship and 123 were from other European countries. The mineralization status of lower third molars was evaluated based on Demirjian's classification of stages. For the statistical assessment of data, logistic regression and mean value testing were used. The findings show that completed growth in wisdom teeth is observable at ages less than 18. Male individuals were approximately 1year ahead of females at stage H, and South East Europeans were approximately 6months ahead of Swiss (Central Europe) at stage H. Mean values led to false conclusions regarding the question of the attained age of 18. Therefore, regression analysis should be used for the statistical assessment of data in dental age diagnostic

Measuring frontier orbital energy levels of OLED materials using cyclic voltammetry in solution

The operation of organic light emitting diodes (OLEDs) is governed by a range of material parameters, such as frontier orbital energy levels, charge carrier mobility and excitonic rate parameters. In state-of-the art numerical simulations of OLED devices, more than 30 parameters must be considered to describe the behavior of a multilayer device. Independent measurement techniques to reliably determine each material parameter individually are therefore highly desirable. While several techniques have been established in the OLED community to determine some of them, the highest occupied and lowest unoccupied molecular orbital (HOMO and LUMO) energy levels are not measured or reported on a regular basis, despite their significant influence on device performance. In this work, we show how cyclic voltammetry in solution can be used as a simple technique to measure the HOMO and LUMO energy levels of organic semiconductors. This easily performed experiment allows a fairly accurate estimation of the energy levels of the layers in a device stack. Cyclic voltammetry measurements of four typical OLED materials in solution are presented and their analysis is described in detail to encourage more such measurements in future OLED studies. Four distinctly different voltammograms were obtained, ranging from relatively ideal reversible behavior to a very non-ideal behavior, lacking electrochemical reverse reactions. Two methods for extracting the HOMO and LUMO energy levels from cyclic voltammetry are discussed and compared. The measured HOMO and LUMO levels compare well with reported values measured on thin films, showing that cyclic voltammetry in solution provides a viable means to determine this important, yet underinvestigated material property

Oxaliplatin combined with irinotecan and 5-fluorouracil/leucovorin (OCFL) in metastatic colorectal cancer: a phase I-II study

Background:: A phase I-II multicenter trial was conducted to define the maximal tolerated dose and describe the activity of an OCFL combination using oxaliplatin (OHP), irinotecan (CPT-11) and 5-fluorouracil (FU)/leucovorin (LV) in metastatic colorectal cancer (CRC). Patients and methods:: CRC patients not pretreated with palliative chemotherapy, with performance status ≤1 and adequate haematological, kidney and liver function, were eligible. Treatment consisted in weekly 24-h infusion 5-FU (2300 mg/m2)/LV (30 mg) and alternating OHP (70-85 mg/m2, days 1 and 15) and CPT-11 (80-140 mg/m2, days 8 and 22) repeated every 5 weeks. OHP and CPT-11 were escalated in cohorts of three to six patients. Results:: Thirty patients received a median of five cycles. Dose-limiting toxicity occurred at dose level 3, and the recommended dose was OHP 70 mg/m2, CPT-11 100 mg/m2, LV 30 mg and 5-FU 2300 mg/m2/24 h. Grade ≥3 toxicities were diarrhea 23%, neutropenia 20%, fatigue 7%, and neurologic 7%. Two febrile neutropenia episodes (one fatal) were recorded. Among 28 patients with measurable disease (90%), we observed two complete and 20 partial responses; overall RR was 78% (95% CI, 59% to 92%). Median time to progression and overall survival were 9.5 and 25.4 months, respectively. Seven patients underwent liver metastases resection. Conclusion:: OCFL is an overall well tolerated regimen with very high efficacy, which makes it most suitable for tumour control before surgery of metastatic diseas

Pinpointing the origin of the increased driving voltage during prolonged operation in a phosphorescent OLED based on an exciplex host

We report on the origin of the reduced power efficiency in a red phosphorescent OLED with an exciplex host after prolonged operation. The power efficiency is reduced solely by an increased driving voltage while the radiant flux remains constant. An electrical model describing the driving voltage increase is, thus, sufficient to explain the reduced power efficiency. The electrical model of the fresh OLED and at different stages of degradation was devised from four different measurement methods. Using multiple measurement methods to determine the model parameters results in a rather unique set of model parameters, despite the large number of model parameters (38) as revealed by a correlation analysis. The increase in driving voltage could be reproduced by modifying only 7 out of the 38 model parameters. A sensitivity analysis identified the parameters with the largest effect (66%) on the driving voltage increase to be the trap density and the mobility of the employed hole transporting layer. This work highlights the benefit of using multiple measurement methods to derive reliable model parameters and the use of a sensitivity analysis to pinpoint the origin of the investigated property

Simulations, measurements and optimization of OLEDs with scattering layer

A multi-scale optical model for organic light-emitting devices containing scattering layers is presented. This model describes the radiation of embedded oscillating dipoles and scattering from spherical particles. After successful model validation with experiments on a top-emitting white OLED, we show how this tool can be used for optimization with specific targets

Consistent Device Simulation Model Describing Perovskite Solar Cells in Steady-State, Transient, and Frequency Domain

A variety of experiments on vacuum-deposited methylammonium lead iodide perovskite solar cells are presented, including JV curves with different scan rates, light intensity-dependent open-circuit voltage, impedance spectra, intensity-modulated photocurrent spectra, transient photocurrents, and transient voltage step responses. All these experimental data sets are successfully reproduced by a charge drift-diffusion simulation model incorporating mobile ions and charge traps using a single set of parameters. While previous modeling studies focused on a single experimental technique, we combine steady-state, transient, and frequency-domain simulations and measurements. Our study is an important step toward quantitative simulation of perovskite solar cells, leading to a deeper understanding of the physical effects in these materials. The analysis of the transient current upon voltage turn-on in the dark reveals that the charge injection properties of the interfaces are triggered by the accumulation of mobile ionic defects. We show that the current rise of voltage step experiments allow for conclusions about the recombination at the interface. Whether one or two mobile ionic species are used in the model has only a minor influence on the observed effects. A delayed current rise observed upon reversing the bias from +3 to -3 V in the dark cannot be reproduced yet by our drift-diffusion model. We speculate that a reversible chemical reaction of mobile ions with the contact material may be the cause of this effect, thus requiring a future model extension. A parameter variation is performed in order to understand the performance-limiting factors of the device under investigation

Extended light scattering model incorporating coherence for thin-film silicon solar cells

We present a comprehensive scalar light-scattering model for the optical simulation of silicon thin film solar cells. The model integrates coherent light propagation in thin layers with a direct, noniterative treatment of light scattered at rough layer interfaces. The direct solution approach ensures computational efficiency, which is a key advantage for extensive calculations in the context of evaluation of different cell designs and parameter extraction. We validate the model with experimental external quantum efficiency spectra of state-of-the-art microcrystalline silicon solar cells. The simulations agree very well with measurements for cells deposited on both rough and flat substrates. The model is then applied to study the influence of the absorber layer thickness on the maximum achievable photocurrent for the two cell types. This efficient numerical framework will enable a quantitative model-based assessment of the optimization potential for light trapping in textured thin film silicon solar cells

Adding cetuximab to capecitabine plus oxaliplatin (XELOX) in first-line treatment of metastatic colorectal cancer: a randomized phase II trial of the Swiss Group for Clinical Cancer Research SAKK

Background: To determine the activity and tolerability of adding cetuximab to the oxaliplatin and capecitabine (XELOX) combination in first-line treatment of metastatic colorectal cancer (MCC). Patients and methods: In a multicenter two-arm phase II trial, patients were randomized to receive oxaliplatin 130 mg/m2 on day 1 and capecitabine 1000 mg/m2 twice daily on days 1-14 every 3 weeks alone or in combination with standard dose cetuximab. Treatment was limited to a maximum of six cycles. Results: Seventy-four patients with good performance status entered the trial. Objective partial response rates after external review and radiological confirmation were 14% and 41% in the XELOX and in the XELOX + Cetuximab arm, respectively. Stable disease has been observed in 62% and 35% of the patients, with 76% disease control in both arms. Cetuximab led to skin rash in 65% of the patients. The median overall survival was 16.5 months for arm A and 20.5 months for arm B. The median time to progression was 5.8 months for arm A and 7.2 months for arm B. Conclusion: Differences in response rates between the treatment arms indicate that cetuximab may improve outcome with XELOX. The correct place of the cetuximab, oxaliplatin and fluoropyrimidine combinations in first-line treatment of MCC has to be assessed in phase III trial