Improving the color purity and efficiency of blue organic light-emitting diodes (BOLED) by adding hole-blocking layer

This work demonstrates the fabrication of a bright blue organic light-emitting diode (BOLED) with good color purity using 4,4′-bis(2,2-diphenylvinyl)-1,1′-biphenyl (DPVBi) and bathocuproine (BCP) as the emitting layer (EML) and the hole-blocking layer (HBL), respectively. Devices were prepared by vacuum deposition on indium tin oxide (ITO)-glass substrates. The thickness of DPVBi used in the OLED has an important effect on color and efficiency. The blue luminescence is maximal at 7670 cd/m² when 13 V is applied and the BCP thickness is 2 nm. The CIE coordinate at a luminance of 7670 cd/m² is (0.165, 0.173). Furthermore, the current efficiency is maximum at 4.25 cd/A when 9 V is applied.     

Many-body effect in the N23-VV Auger-photoelectron coincidence spectroscopy (APECS) spectra of Ag metal

The coincidence N23-VV Auger-electron spectroscopy (AES) spectra and N23 photoelectron spectroscopy (PES) spectra of Ag metal are analyzed. Here NX is the notation for atomic shell Nx (X = 2, 3). The band-like feature in the coincidence N23-VV AES spectra is much more intense than that in the coincidence M45-VV ones because the potential in the delocalized two-hole state is less attractive than that in the localized one. The partial N23-VV super Coster–Kronig (sCK) transition rate depends critically on both the final-state potential and the sCK-electron kinetic energy (KE) because the KE is low, whereas the partial M45-VV Auger-transition rate is fairly independent of them because the KE is very high. As a result, the partial sCK-transition rate to the band-like state is enhanced compared to that to the atomic-like localized state. The low KE tail in the coincidence N23-VV AES spectra which is likely due to the sCK transition involving more than two electrons, is more enhanced than that in the coincidence M45-VV ones. This is due to the enhancement of the partial sCK-transition rate by the presence of extra holes in the final state. The sharp peaks of small intensity on the lower KE side of the main line in the coincidence N2 PES spectrum are tentatively attributed to the shakeup satellites.     

1.0 MeV电子辐照致VO_2(B)薄膜结构与光谱改变研究

本文以能量为1.0 MeV的电子束辐照VO2(B)薄膜,对电子辐照在薄膜中产生的缺陷进行了理论计算,同时使用X射线衍射仪、原子力显微镜、分光光度计对薄膜进行测试,分析了电子辐照对薄膜结构、形貌与紫外-可见光谱(280~880nm)的影响。结果显示:电子辐照可以在薄膜中引入点缺陷并产生退火效应,电子辐照使薄膜的表面晶粒细化,辐照后薄膜光谱的吸收峰位发生移动,其移动的最大位移达到21nm,辐照后薄膜的光学禁带宽度也有所增加。     

Stage2沉积速率对低温生长CIGS薄膜特性及器件的影响

研究了三步法第二步沉积速率对低温生长Cu(In,Ga)Se₂薄膜结构、 电学特性和器件特性的影响. 通过改变第二步沉积速率发现, 提高沉积速率可以显著促进薄膜晶粒生长, 提高晶粒紧凑程度降低晶界复合, 同时有效改善两相分离现象, 提高电池的开路电压和短路电流, 有助于Cu(In,Ga)Se₂电池光电转换效率的提高. 但同时研究表明, 随着第二步沉积速率的增加, 会促进暂态Cu_2-xSe晶粒的生长, 引起Cu(In,Ga)Se₂薄膜表面粗糙度增大, 并阻碍Na向Cu(In,Ga)Se₂薄膜表面的扩散, 造成施主缺陷钝化效应降低, 薄膜载流子浓度下降和电阻率升高, 且过高的沉积速率会引起电池内部复合增加并产生分流路径, 造成开路电压下降进而引起电池效率恶化. 最终, 通过最佳化第二步沉积速率, 在衬底温度为420℃时, 得到最高转换效率为11.24%的Cu(In,Ga)Se₂薄膜太阳电池.     

Effect of surface chemisorption on the spin reorientation transition in magnetic ultrathin Fe film on Ag(0 0 1)

We have investigated the effect of surface chemisorption on the spin reorientation transitions in magnetic ultrathin Fe films on Ag(0 0 1) by means of the polar and longitudinal magneto-optical Kerr effect (MOKE) and X-ray magnetic circular dichroism (XMCD) measurements. It is found by the MOKE that adsorption of O₂ and NO induces the shift of the critical thickness for the transitions to a thinner side, together with the suppression of the remanent magnetization and the coercive field of the Fe film. This implies destabilization of the perpendicular magnetic anisotropy. On the other hand, H₂ adsorption is found not to change the magnetic anisotropy, though the enhancement of the coercive field is observed. The XMCD reveals that although both the spin and orbital magnetic moments along the surface normal are noticeably reduced upon O₂ and NO adsorption, the reduction of the orbital magnetic moments are more significant. This indicates that the destabilization of the perpendicular magnetic anisotropy upon chemisorption of O₂ and NO originates from the change of the spin-orbit interaction at the surface.     

Doping dependent metal to insulator transition in the (Bi,Pb)-2212 system: The evolution of structural and electronic properties with europium substitution

The present work investigates the effect of europium substitution on the(Bi,Pb)-2212 system in the concentration range 0.5 ≤ x ≤ 1.0.Phase analysis and lattice parameter calculations on the powder diffraction data and the elemental analysis of EDX show that the Eu atoms are successfully substituted into the(Bi,Pb)-2212 system.Resistivity measurements(64-300 K) reveal that the system exhibits superconductivity at x ≤ 0.5 and semiconductivity at x > 0.5.With the complete suppression of superconductivity which is known to be a quasi-two dimensional phenomenon in these materials,a metal to insulator transition takes place at x = 0.6 and the predominant conduction mechanism is found to be variable range hopping between localized states,resulting in macroscopic semiconducting behaviour.The results of electrical and structural properties of the doped(Bi,Pb)-2212 compounds suggest that the decrease of charge carrier concentration and the induced structural disorder are the more effective and dominant mechanisms in the origin of the metal to insulator transition and suppression of superconductivity due to Eu substitution at its Sr site.