Strategies Toward Efficient Blue Perovskite Light-Emitting Diodes

Substantial progress has been made in blue perovskite light-emitting diodes (PeLEDs). In this review, the strategies for high-performance blue PeLEDs are described, and the main focus is on the optimization of the optical and electrical properties of perovskites. In detail, the fundamental device working principles are first elucidated, followed by a systematical discussion of the key issues for achieving high-quality perovskite nanocrystals (NCs) and quasi-2D perovskites. These involve ligand optimization and metal doping in enhancing the carrier transport and reducing the traps of perovskite NCs, as well as the perovskite phase modulation and defect passivation in improving energy transfer and emission efficiency of quasi-2D perovskites. The strategies for efficient 3D mixed-halide perovskite and lead-free perovskite blue LEDs are then briefly introduced. After that, other strategies, including effective charge transport layer, efficient perovskite emission system, and effective device architecture for high light outcoupling efficiency, are further discussed to boost the blue PeLED performances. Meanwhile, the testing standard of blue PeLED lifetime is suggested to enable the direct comparisons of the device operational stability. Finally, challenges and future directions for blue PeLEDs are addressed.     

Structural, electrical and magnetic characterizations of Ni/Cu/p-Si Schottky diodes prepared by liquid phase epitaxy

In this paper, we have investigated the structural, electrical and magnetic characterizations of Ni/Cu/p-Si Schottky diode prepared by liquid phase epitaxy (LPE). Current density-voltage (J-V), capacitance-voltage (C-V) and capacitance-frequency (C-f) measurements were performed to determine the conduction mechanisms as well as extracting the important diode parameters. Rectifying properties were obtained, which definitely of the Schottky diode type. At low voltages, (0 < V ? 0.4 V), current density in the forward direction was found to obey the diode equation, while for higher voltages, (0.5 < V ? 1.5 V), conduction was dominated by a space-charge-limited conduction (SCLC) mechanism. Analysis of the experimental data under reverse bias suggests a transition from electrode-limited to a bulk-limited conduction process for lower and higher applied voltages, respectively. Diode parameters such as, the built-in potential, V_b, the carrier concentration, N, the width of the depletion layer, W, of the Ni/Cu/p-Si Schottky diode were obtained from the C-V measurements at high frequency (1 MHz). The capacitance-frequency measurements showed that the values of capacitance were highly frequency dependent at low frequency region but independent at high frequencies. The Ni/Cu/p-Si Schottky diode showed magnetic properties due to the effect of Ni in the heterostructure.     

ICP-induced defects in GaN characterized by capacitance analysis

The defects induced by inductively coupled plasma reactive ion etching (ICP-RIE) on a Si-doped gallium nitride (GaN:Si) surface have been analyzed. According to the capacitance analysis, the interfacial states density after the ICP-etching process may be higher than 5.4 × 10¹² eV⁻¹ cm⁻², compared to around 1.5 × 10¹¹ eV⁻¹ cm⁻² of non-ICP-treated samples. After the ICP-etching process, three kinds of interfacial states density are observed and characterized at different annealing parameters. After the annealing process, the ICP-induced defects could be reduced more than one order of magnitude in both N₂ and H₂ ambient. The H₂ ambient shows a better behavior in removing ICP-induced defects at a temperature around 500 °C, and the interfacial states density around 2.2 × 10¹¹ eV⁻¹ cm⁻²can be achieved. At a temperature higher than 600 °C, the N₂ ambient provides a much more stable interfacial states behavior than the H₂ ambient.     

Unterminated 4H-SiC Schottky barrier diodes with novel HfNxBy electrodes

4H-SiC Schottky barrier diodes (SBDs) were fabricated and characterized from room temperature to 573 K using HfN_xB_y as Schottky electrodes. The results are compared to SBDs fabricated using other electrodes that include Ni, Pt, Ti and Au. The Schottky barrier height Φ_b for as-deposited HfN_xB_y/n−/n+ diodes, determined from room temperature current-voltage characteristics, is 0.887 eV. This is lower than those of SBDs fabricated using other metals such as Au, where Φ_b is 1.79 eV. The HfN_xB_y/n−/n+ diodes studied have a much higher on-resistance R_on of around 38.24 mΩ-cm², which is about four times that of Au/n−/n+ diodes, due to the higher sheet resistance of the sputtered HfN_xB_y electrode layer. The barrier height Φ_b and ideality factor η of the HfN_xB_y/n−/n+ diodes remain almost unchanged after 400 and 750 °C anneal in N₂. This suggests excellent thermal and chemical stability of HfN_xB_y in contact with 4H-SiC.     

Fabrication of ZnO-based metal–insulator–semiconductor diodes by ion implantation

A ZnO-based metal–insulator–semiconductor junction has been fabricated using an isolation layer fabricated by N⁺ ion implantation. I–V dependences show a good rectifying diode-like behavior with a low leakage current of 10⁻⁶ A and a threshold voltage of about 3 V. Ultraviolet light emission under forward bias exhibits a wavelength maximum of 388 nm and a full width at half maximum of 128 meV at room temperature.     

微纳米PIN电光调制器的优化

在微纳米PIN电光调制器的基础上,分析了载流子浓度对其调制特性的影响。根据注入调制区载流子平均浓度随时间变化关系,采用在驱动信号中加入正反向预加重电压的调制电压方式,不仅可以提高注入载流子浓度,而且可以缩短反向抽取载流子所用的时间,从而有效提高电光调制器的调制速度;详细分析了PIN电光调制器结构中内脊高度H、外脊高度h,波导脊宽W以及重掺杂区到波导的距离Ws等参数对其调制特性的影响;最终根据数据的分析,给出了优化后的参数,制作了电光调制器并进行了测试,测试结果验证了文中数据分析的正确性。     

Rapid Combinatorial Synthesis and Chromatography Based Screening of Phosphorescent Iridium Complexes for Solution Processing

This work reports the combinatorial synthesis and screening of phosphorescent iridium complexes as solution processable emitters for OLEDs. The approach taken here allows for the rapid synthesis, isolation, spectroscopic characterization and identification of the libraries based on chromatographic methods. Subsequent analysis of the irradiation induced degradation provides insight on the stability of the complexes under continuous excitation. The method is versatile and can easily be applied to other metal complexes or organic dyes for various applications, e.g., in electroluminescence, photovoltaics and sensing.     

JTE结构4H-SiC肖特基二极管的研究

借助半导体仿真软件Silvaco,仿真一种具有结终端扩展（JTE）结构的碳化硅（SiC）肖特基二极管（SBD）。其机理是通过JTE结构降低肖特基结边缘的电场集中效应,从而优化肖特基二极管的反向耐压能力。研究JTE区深度、宽度及掺杂浓度对碳化硅肖特基二极管的反向耐压的影响。通过优化结终端结构的结构参数使碳化硅肖特基二极管的反向耐压特性达到更好的性能要求。     

Co‐Interlayer Engineering toward Efficient Green Quasi‐Two‐Dimensional Perovskite Light‐Emitting Diodes

With respect to three‐dimensional (3D) perovskites, quasi‐two‐dimensional (quasi‐2D) perovskites have unique advantages in light‐emitting devices (LEDs), such as strong exciton binding energy and good phase stability. Interlayer ligand engineering is a key issue to endow them with these properties. Rational design principles for interlayer materials and their processing techniques remain open to investigation. A co‐interlayer engineering strategy is developed to give efficient quasi‐2D perovskites by employing phenylbutylammonium bromide (PBABr) and propylammonium bromide (PABr) as the ligand materials. Preparation of these co‐interlayer quasi‐2D perovskite films is simple and highly controllable without using antisolvent treatment. Crystallization and morphology are readily manipulated by tuning the ratio of co‐interlayer components. Various optical techniques, including steady and ultrafast transient absorption and photoluminescence spectroscopies, are used to investigate their excitonic properties. Photoluminescence quantum yield (PLQY) of the perovskite film is dramatically improved to 89% due to the combined optimization of exciton binding energy and suppression of trap state formation. Accordingly, a high current efficiency of 66.1 cd A^?1 and an external quantum efficiency of 15.1% are achieved for green co‐interlayer quasi‐2D perovskite LEDs without using any light out‐coupling techniques, indicating that co‐interlayer engineering is a simple and effective approach to develop high‐performance perovskite electroluminescence devices.