Current Issue : January-March Volume : 2022 Issue Number : 1 Articles : 5 Articles
CdSe/ZnS quantum dots (QDs) have attracted great consideration from investigators owing to their excellent photo-physical characteristics and application in quantum dot light-emitting diodes (QD-LEDs). The CdSe/ZnS-based inverted QD-LEDs structure uses high-quality semiconductors electron transport layers (ETLs), a multilayered hole transporting layers (HTLs). In QD-LED, designing a device structure with a minimum energy barrier between adjacent layers is very important to achieve high efficiency. A high mobility polymer of poly (9,9-dioctylfluorene-co-N-(4-(3-methylpropyl)) diphenylamine (TFB) was doped with 4,40-bis-(carbazole-9-yl) biphenyl (CBP) with deep energy level to produce composite TFB:CBP holes to solve energy mismatch (HTL). In addition, we also improved the QD-LED device structure by using zinc tin oxide (ZTO) as ETL to improve device efficiency. The device turn-on voltage Vt (1 cd m2) with ZTO ETL reduced from 2.4 V to 1.9 V significantly. Furthermore, invert structure devices exhibit luminance of 4296 cd m2, current-efficiency (CE) of 7.36 cd A1, and external-quantum efficiency (EQE) of 3.97%. For the QD-LED based on ZTO, the device efficiency is improved by 1.7 times....
Here, we report the hole injection role of p-type conjugated polymer layer in phosphorescent organic light-emitting devices (OLEDs). Poly(3-hexylthiophene) (P3HT) nanolayers (thickness = ~1 nm thick), which were subjected to thermal annealing at 140 C by varying annealing time, were inserted between indium tin oxide (ITO) anodes and hole transport layers (N,N0- bis(naphthalen-1-yl)-N,N0-bis(phenyl)-benzidine, NPB). The 1 nm-thick P3HT layers showed very weak absorption in the visible light range of 500~650 nm. The device results disclosed that the presence of P3HT layers were just able to improve the charge injection of OLEDs leading to an enhanced luminance irrespective of thermal annealing condition. The highest luminance and efficiency were achieved for the OLEDs with the P3HT layers annealed at 140 C for 10 min. Further annealing for 30 min resulted in turn-down of device performances. The emission color was almost unchanged by the presence of P3HT layers even though the color coordinates were marginally fluctuated according to the annealing time. The present result delivers the possibility to use p-type conjugated polymers (i.e., P3HT) as a hole injection layer in OLEDs....
We fabricated indium gallium nitride (InGaN) red light-emitting diodes (LEDs) with a peak emission wavelength of 649 nm and investigated their electroluminescence (EL) properties. An additional separated peak in the EL spectrum of the red LEDs at 20 mA was observed at 465 nm. This additional peak also exhibits a blue-shift with increasing currents as does the main emission peak. Using high-resolution microscopy, we observed many point-like emission spots in the EL emission images at the currents below 1 mA. However, these emission spots cannot be identified at currents above 5 mA because the red emission from quantum wells (QWs) is much stronger than that emitted by these spots. Finally, we demonstrate that these emission spots are related to the defects generated in red QWs. The measured In content was lower at the vicinity of the defects, which was regarded as the reason for separated short-wavelength emission in red InGaN LEDs....
This work proposes a piecewise modeling of output‐voltage ripple for linear charge pumps. The proposed modeling can obtain a more accurate design expression of power‐conversion efficiency. The relationship between flying and output capacitance, as well as switching frequency and optimize power‐conversion efficiency can be calculated. The proposed modeling is applied to three charge‐pump circuits: 1‐stage linear charge pump, dual‐branch 1‐stage linear charge pump and 4× cross‐coupled charge pump. Circuit‐level simulation is used to verify the accuracy of proposed modeling....
The increase in industrial and commercial applications of photovoltaic systems (PV) has a significant impact on the increase in interest in studying the improvement of the efficiency of these systems. Estimating the efficiency of PV is considered one of the most important problems facing those in charge of manufacturing these systems, which makes it interesting to many researchers. The difficulty in estimating the efficiency of PV is due to the high non-linear current–voltage characteristics and power–voltage characteristics. In addition, the absence of ample efficiency information in the manufacturers’ datasheets has led to the development of an effective electrical mathematical equivalent model necessary to simulate the PV module. In this paper, an application for an optimization algorithm named Wild Horse Optimizer (WHO) is proposed to extract the parameters of a double-diode PV model (DDM), modified double-diode PV model (MDDM), triple-diode PV model (TDM), and modified triple-diode PV model (MTDM). This study focuses on two main objectives. The first concerns comparing the original models (DDM and TDM) and their modification (MDDM and MTDM). The second concerns the algorithm behavior with the optimization problem and comparing this behavior with other recent algorithms. The evaluation process uses different methods, such as Root Mean Square Error (RMSE) for accuracy and statistical analysis for robustness. Based on the results obtained by the WHO, the estimated parameters using the WHO are more accurate than those obtained by the other studied optimization algorithms; furthermore, the MDDM and MTDM modifications enhanced the original DDM and TDM efficiencies....
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