基于Ir(ppy)2acac的掺杂浓度对 OLED器件发光性能影响研究

制备了结构为:ITO/MoO3(40nm)/NPB(40nm)/TCTA(10nm)/CBP:Ir(ppy)2acac(x%)(30nm)/BCP(10nm)/Alq3(40nm)/LiF(1nm)/Al(100nm)的器件,Ir(ppy)2acac为绿色磷光染料,x分别为4%、6%、8%、10%。通过调节绿色磷光染料的掺杂浓度,对器件的发光性能进行了研究,发现在掺杂浓度为8%,亮度为490cd/m2,器件获得最高电流效率为69.43cd/A,相比4%的器件高出27.5%。分析原因是掺杂浓度越高,载流子在绿色染料上复合的几率越高;CBP与Ir(ppy)2acac的LUMO能级均为2.5eV,注入主体CBP上的电子可以直接传递给掺杂染料,避免电子对掺杂染料传递过程中的能量损失;较高的掺杂浓度更有利于载流子的传输。然而,较高的掺杂浓度会引起三线态激子的猝灭效应。另外,由于TCTA、BCP为载流子阻挡材料,具有较高的三线态能量,可以将载流子和激子限制在发光层内。     

Possibility of obtaining the (GaSb)1 − x (Si2) x films on silicon substrates by the method of liquid-phase epitaxy

Semiconductors - It is shown that it is possible to grow a continuous series of (GaSb)1 ? x (Si2) x (x = 0?1) alloys on silicon substrates by the method of liquid-phase epitaxy from a...     

Charge Transfer in Gap Structures Based on the Chalcogenide System (As2Se3)100 –xBix

Semiconductors - The results of investigating charge-transfer processes in thin layers of a vitreous system (As2Se3)100 – xBix are presented. A power-law dependence of the...     

Effect of bath temperature on the properties of CuIn_χGa_(1-χ)Se_2 thin films grown by the electrodeposition technique

Electrodeposition is a promising and low cost method to synthesize CuIn_xGa_(1-x)Se_2(CIGS)thin films as an absorber layer for solar cells.The effect of bath temperature on the properties of CIGS thin films was investigated in this paper.CIGS films of 1μm thickness were electrodeposited potentiostatically from aqueous solution,containing trisodium citrate as a complexing agent,on Mo/glass substrate under a voltage of-0.75 V,and bath temperatures were varied from 20 to 60℃.The effects of bath temperature ...     

Study of the recombination process at crystallite boundaries in CuIn1 − x Ga x Se2 (CIGS) films by microwave photoconductivity

The loss kinetics of photogenerated charge carriers in thin polycrystalline chalcopyrite CuIn_1?x Ga _x Se₂ (CIGS) films has been studied by microwave photoconductivity (at 36 GHz). The films were synthesized using the ampoule method and three variants of physical vapor deposition with subsequent selenization: magnetron sputtering, thermal deposition, and modified thermal deposition with intermetallic precursors. The photoconductivity was excited by 8-ns nitrogen laser pulses with maximum intensity of 4 × 10¹⁴ photons/cm per pulse. Measurements were performed in the temperature range 148–293 K. The photoresponse amplitude is found to depend linearly on the sizes of coherent-scattering regions in the film grains, which were calculated from X-ray diffraction data. The photoresponse decay obeys hyperbolic law. The photoresponse half-decay time increases with a decrease in both temperature and light intensity. It is shown that the recombination of free holes with trapped electrons is very efficient near the crystallite boundaries.     

Light emitting diodes for the spectral range λ=3.3–4.3 µm fabricated from InGaAs and InAsSbP solid solutions: Electroluminescence in the temperature range of 20–180°C (Part 2)

Light-emitting diodes (LEDs) based on p-n homo-and heterostructures with InAsSb(P) and InGaAs active layers have been designed and studied. An emission power of 0.2 (λ=4.3 µm) to 1.33 mW (λ=3.3 µm) and a conversion efficiency of 30 (InAsSbP, λ=4.3 µm) to 340 mW/(A cm²) (InAsSb/InAsSbP double heterostructure (DH), λ=4.0 µm) have been achieved. The conversion efficiency decreases with increasing current, mainly owing to the Joule heating of the p-n homojunctions. In DH LEDs, the fact that the output power tends to a constant value with increasing current is not associated with active region heating. On raising the temperature from 20 to 180°C, the emission power of the (λ=3.3 and 4.3 µm) LEDs decreases, respectively, 7-and 14-fold, to become 50 (at 1.5 A) and 7 µW (at 3 A) at 180°C.     

Deposition of heteroepitaxial layers of topological insulator Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript> in the trimethylbismuth–isopropylselenide–hydrogen system on the (0001) Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and (100) GaAs substrates

Thin solid layers that are formed upon heating of the gaseous trimethylbismuth–isopropylselenide–hydrogen system on the (0001) Al₂O₃ and singular and vicinal (100) GaAs surfaces are studied. The conditions for deposition of metal Bi and phases of Bi₄Se₃, BiSe, and topological insulator Bi₂Se₃ using the MOCVD method are determined. Pure metastable phase BiSe is obtained for the first time. Bi₂Se₃ films with a thickness of no less than 200 nm, a relatively low volume concentration of 3 ×10¹⁸ cm^–3, and a high mobility of carriers at 300 K (1000 cm² V^–1 s^–1) are fabricated.     

Effect of Ionic Radius and Resultant Two-Dimensionality of Phonons on Thermal Conductivity in M<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>CoO<Subscript>2</Subscript> (M = Li,Na, K) by Perturbed Molecular Dynamics

Phonon thermal conductivity calculations for Li _x CoO₂, Na _x CoO₂, and K _x CoO₂ (x = 1, 0.5) have been carried out by perturbed molecular dynamics to clarify the dependence of thermal conductivity on alkali-metal vacancy concentration in these materials. While thermal conductivity decreased for all compounds upon introduction of alkali-metal vacancies, the magnitude of the decrease is strongly dependent on the size of the alkali-metal ion. Further numerical analyses using fictitious physical parameters reveal that, with increasing ionic radius, the two-dimensionality of the phonons in the CoO₂ layers, which are responsible for overall thermal conductivity, is enhanced, resulting in lower thermal conductivity in vacancy-free compounds as well as ineffectiveness of alkali-metal vacancies in lowering thermal conductivity. In contrast, for systems with smaller alkali-metal ionic radius, even though higher thermal conductivity is predicted when no vacancies are present, vacancies are quite effective in significantly lowering thermal conductivity by modifying phonon states in the CoO₂ layers, more so than in systems with larger alkali-metal vacancies.