Electronic structures at organic heterojunctions of N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamin (NPB)-based organic light emitting diodes

Interface electronic structures of four-kinds of electron transporting or hole blocking organic materials (n-type) on a widely-used hole transporting material (p-type) in organic light emitting diodes (OLEDs), N,N′-bis (1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamin (NPB), were investigated by means of photoelectron spectroscopy (PES). 1,3-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene (OXD-7) and 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) overlayers show continuous energy shift of each overlayer-derived spectral components and the vacuum level proportional to the thickness. This energy shift is ascribed to a spontaneous building up of the electrostatic potential within the organic layers (giant surface potential; GSP). The energy shift of the overlayers induced by GSP as well as the interface vacuum level shift are adequately taken into account to determine the actual energy barrier heights of the hole conduction levels at the heterojunctions. 4,4′-bis(9-carbazolyl)biphenyl (CBP) and p-bis(triphenylsilyl) benzene (UGH2) induce band bending in the NPB film which presumably results from charge transfer (CT) to the n-type materials from NPB. Despite absence of a practical vacuum level shift and thickness dependent shift of the overlayer-derived electronic states, the CT-derived energy shift of NPB reduces the actual energy barrier height with respect to the nominal barrier height being simply interpreted from PES spectra of a thick overlayer of each material. The energy level diagrams across these ‘n-on-p’ organic–organic heterojunctions were finely determined based on the above interpretation of the PES spectra.     

Air-stability and bending properties of flexible organic field-effect transistors based on poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]

We have fabricated flexible field-effect transistors (FETs) using poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)], PCDTBT, as an active channel, poly(methyl methacrylate) (PMMA) as gate dielectric and biaxially oriented polyethyleneterephthalate (BOPET) as supporting substrate. The output and transfer characteristics of the devices were measured as a function of channel length. It has been observed that various OFET parameters viz. on–off ratio (∼10⁵), mobility (μ ∼ 10⁻⁴ cm² V⁻¹ s⁻¹), threshold voltage (V_th ∼ −14 V), switch-on voltage (V_so ∼ −6 V), subthreshold slope (S ∼ 7 V/decade) and trap density (N_it ∼ 10¹⁴ cm⁻² V⁻¹) are almost independent of the channel length, which suggested a very high uniformity of the PCDTBT active layer. These devices were highly stable under atmospheric conditions (temperature: 20–35 °C and relative humidity: 70–85%), as no change in mobility was observed on a continuous exposure for 70 days. The studies on the effect of strain on mobility revealed that devices are stable up to a compressive or tensile strain of 1.2%. These results indicate that PCDTBT is a very promising active layer for the air stable and flexible FETs.     

Efficient 4,4′,4″‐tris(3‐methylphenylphenylamino)triphenylamine (m‐MTDATA) Hole Transport Layer in Perovskite Solar Cells Enabled by Using the Nonstoichiometric Precursors

To overcome the drawbacks of the acidic and hygroscopic nature of the poly(3,4‐ethylenedio‐xythiophene):poly(styrenesulfonate) hole transport layer (HTL), the p‐type polymeric hole transport materials have attracted great attention and have been applied into perovskite solar cells. Here, a starburst amine molecule 4,4′,4″‐tris(3‐methylphenylphenylamino)triphenylamine (m‐MTDATA) without any additive is demonstrated as an effective hole transport material in perovskite solar cells. Meanwhile, considering the different surface affinity of precursor's composition on m‐MTDATA, the influence of the molar ratios between lead iodine (PbI₂) and methylammonium iodide in precursor solution on the perovskite characteristics and device performance is investigated in‐depth. Ultimately, an enhanced efficiency of 17.73% and a high fill factor of 79.6% are achieved, which attribute to the strong passivation effect of traps and small resistance loss from appropriate unreacted PbI₂ left in the perovskite layer. This work not only provides a remarkable HTL, but also reveals that the adjustment of precursor ratio is necessary for the one‐step solution approach, because the affinities of precursor's composition may be different with the underlying transport layers.     

Photoinduced magnetoconductance response of N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine-based diodes: Sign inversion by controlling carrier extraction

We explore the magnetoconductance (MC) response of N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine-based single-layer devices. The MC effect can be observed only if the device is irradiated with light, for measurement voltages |V| < 5 V. A positive MC with a non-Lorentzian line shape is obtained under forward bias. Under reverse bias, however, the MC shows both positive and negative components, forming a “W” shape with dips at about ±100 mT. The sign of the MC under reverse bias can be changed by controlling the carrier extraction from the anode/organic interface. We suggest that the positive MC is caused by triplet–polaron interaction and the negative MC by bipolaron formation.     

Electronic structures of CuI interlayers in organic electronic devices: An interfacial studies of N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine/CuI and tris-(8-hydroxyquinolinato)aluminum/CuI

Electronic structures with the copper iodide (CuI) interlayer in organic electronic devices were measured and its strong electron-withdrawing properties were revealed. In situ ultraviolet and X-ray photoelectron spectroscopy showed the interfacial electronic structures of N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (NPB)/CuI/indium–tin-oxide (ITO) and tris-(8-hydroxyquinolinato)aluminum (Alq₃)/CuI/ITO as a representative hole- and electron-transport material. The large work function of the CuI interlayer induces electron transfer from both molecules and ITO to CuI. As a result, CuI dramatically reduces the hole injection barrier (HIB) from ITO to NPB and Alq₃ layers. Notably, CuI assists molecular ordering of the NPB layer, which would increase the intermolecular interaction, so would enhance the charge transport properties. Simultaneous enhancement in HIB and molecular ordering with the CuI interlayer would improve the device performance.     

PSS掺杂对PEDOT电化学性能的影响

以聚苯乙烯磺酸钠(PSSNa)为掺杂剂,三氯化铁(FeCl3)为氧化剂,通过化学氧化法制备了PEDOT/PSS复合物。利用傅里叶红外光谱表征了所制复合物的组成,通过循环伏安、交流阻抗及恒电流充放电测试研究了反应物摩尔比r(EDOT:PSS)对产物比容量的影响。实验结果表明适量添加PSS可以改善复合物的电容性能。在0.5 mol/L的Na2SO4水溶液中,纯PEDOT材料的比容量可达60 F/g,但其在快速充放电条件下有明显衰减,而摩尔比r(EDOT:PSS)=1:0.5时制备的复合材料比容量则能保持较好的稳定性。当摩尔比r(EDOT:PSS)增大至1:2时所得复合物电容性能下降。     

Si~(4+)掺杂对BaZr(BO_3)_2:Eu荧光粉能量传递的影响

采用高温固相法合成了Si4+掺杂的BaZr(BO3)2:Eu红色发光荧光粉。激发光谱表明,不同Si4+掺杂浓度明显使电荷迁移态(CTS)向高能量的位置移动,且改善了样品的发光强度。分析认为,这是由于Si4+的电负性大于所取代的Zr4+,且Si4+的进入影响了Eu3+的配位数,提高了CTS向发光中心的能量传递几率。依据Judd-Ofelt理论计算的强度参数表明,随着Si4+掺杂浓度的增加,Eu3+所处格位的对称性明显降低,增大了Eu3+的跃迁几率,从而改善了发光强度。计算Eu3+间的能量传递几率发现,在掺杂浓度为5%时,Eu3+间的能量传递几率很小,其对荧光粉的发光影响不大。     

Ca-B-Si掺杂对Ba(Mg_(1/3)Nb_(2/3))O_3陶瓷介电性能的影响

采用传统电子陶瓷工艺合成了Ca-B-Si(CBS)玻璃掺杂的Ba(Mgl/3Nb2/3)O3微波介质陶瓷,研究了CBS掺杂量对陶瓷微波介电性能的影响。结果表明:CBS掺杂可促进陶瓷烧结并提高B位1:2有序度,进而降低微波介质损耗。当w(CBS)=3%时,陶瓷烧结温度由纯相时的1 500℃以上降至1 250℃,表观密度提高到6.32 g/cm3以上,陶瓷的微波介电性能达到最佳值:εr=26,Q.f=67 800 GHz(8 GHz),τf=25×10–6/℃。该陶瓷有望成为用于高频段微波器件的材料。     

BiFeO_3掺杂对CaCu_3Ti_4O_(12)陶瓷结构和介电性能的影响

采用固相反应法制备了BiFeO3掺杂的CaCu3Ti4O12(CCTO)陶瓷,研究了BiFeO3掺杂量对CCTO陶瓷的烧结性能、晶体结构和介电性能的影响。结果表明,BiFeO3掺杂改善了CCTO陶瓷的烧结性能。随BiFeO3掺杂量的增加,CCTO陶瓷的晶格常数和εr均先增大而后减小;而tanδ先几乎不变而后增大。当x(BiFeO3)为0.5%,1040℃烧结的CCTO陶瓷样品在1kHz时具有巨介电常数(εr=14559)和较低的介质损耗(tanδ=0.12)。     

Origins of Improved Hole‐Injection Efficiency by the Deposition of MoO3 on the Polymeric Semiconductor Poly(dioctylfluorene‐alt‐benzothiadiazole)

The electronic structure of the interfaces formed after deposition of MoO₃ hole‐injection layers on top of a polymer light‐emitting material, poly(dioctylfluorene‐alt‐benzothiadiazole) (F8BT), is studied by ultraviolet photoelectron spectroscopy (UPS), X‐ray photoelectron spectroscopy and metastable atom electron spectroscopy. Significant band bending is induced in the F8BT film by MoO₃ “acceptors” that spontaneously diffuse into the F8BT “host” probably driven by kinetic energy of the deposited hot MoO₃. Further deposition leads to the saturation of the band bending accompanied by the formation of MoO₃ overlayers. Simultaneously, a new electronic state in the vicinity of the Fermi level appears on the UPS spectra. Since this peak does not appear in the bulk MoO₃ film, it can be assigned as an interface state between the MoO₃ overlayer and underlying F8BT film. Both band bending and the interface state should result from charge transfer from F8BT to MoO₃, and they appear to be the origin of the hole‐injection enhancement by the insertion of MoO₃ layers between the F8BT light‐emitting diodes and top anodes.     

Na和Ti掺杂对Bi2(Zn1/3Nb2/3)2O7陶瓷性能的影响

采用传统固相反应法制备了Na-Ti掺杂Bi2(Zn1/3Nb2/3)2O7陶瓷。研究了Na+替代Bi3+,Ti4+替代Nb5+对Bi2(Zn1/3Nb2/3)2O7陶瓷烧结特性、显微结构和介电性能的影响。结果表明,掺入Na+和Ti4+后,Bi2(Zn1/3Nb2/3)2O7陶瓷的烧结温度从1000℃降到了860℃左右;在–30℃～+130℃的温度范围内,Na-Ti掺杂Bi2(Zn1/3Nb2/3)2O7陶瓷表现出明显的、激活能约为0.3eV的介电弛豫现象。这主要是由缺陷偶极子和晶格畸变在陶瓷中的出现引起的。     

掺杂Lu_2O_3对Ba_4Sm_(9.33)Ti_(18)O_(54)微波介质陶瓷性能的影响

以Ba4Sm9.33Ti18O54微波介质陶瓷为基础,掺杂Lu2O3进行改性,形成固溶式为Ba4(Sm1–yLuy)9.33Ti18O54的结构。结果表明,掺杂Lu2O3能很好地把Ba4Sm9.33Ti18O54微波介质陶瓷的烧结温度降至1 260℃,当y=0.05时Ba4Sm9.33Ti18O54为类钨青铜结构,能得到介电性能较佳的微波介质陶瓷:4.33GHz时εr约为76,Q.f约为2532,τf为–42×10–6/℃;y<0.5时生成了类钨青铜结构晶相,y≥0.5主晶相变成烧绿石相,不具备介电性。     

Influence of Ni Schottky contact thickness on two-dimensional electron-gas sheet carrier concentration of strained Al_(0.3)Ga_(0.7)N/GaN heterostructures

Ni/Au Schottky contacts with thicknesses of either 50(?)/50(?) or 600(?)/2000(?) were deposited on strained Al_(0.3)Ga_(0.7)N/GaN heterostructures.Using the measured C-V curves and I-V characteristics at room temperature,the calculated density of the two-dimensional electron-gas(2DEG) of the 600(?)/2000(?) thick Ni/Au Schottky contact is about 9.13×10~(12) cm~(-2) and that of the 50(?)/50(?) thick Ni/Au Schottky contact is only about 4.77×10~(12) cm~(-2).The saturated current increases from 60.88 to 86.3...     

钛酸铋掺杂对BaTiO3-Nb2O5-ZnO陶瓷微结构和介电性能的影响

采用固相反应法制备了Bi4Ti3O12(BIT)掺杂的BaTiO3-Nb2O5-ZnO(BTNZ)陶瓷,研究了BIT掺杂对所制陶瓷晶体结构、烧结性能及介电性能的影响.结果表明:BIT掺杂改善了BTNZ陶瓷的烧结特性.随着BIT量的增加,四方率c/a增大,电容变化率减小.当质量分数w(BIT)为1.0%,1 230℃烧结...     

BiFeO3/Bi4Ti3O12多层铁电薄膜的性能研究

采用sol-gel法在FTO/玻璃底电极上制备了BiFeO3/Bi4Ti3O12多层薄膜。研究了室温下薄膜的结构,铁电和漏电流性质。结果表明,相对于纯的BiFeO3薄膜,BiFeO3/Bi4Ti3O12多层薄膜具有更低的漏电流,表现出较强的铁电性,在4.40×105V/cm的测试电场强度下,剩余极化强度为3.7×10–5C/cm2。在2.00×105V/cm的测试电场强度下,BiFeO3和BiFeO3/Bi4Ti3O12薄膜的漏电流密度分别为10–5和10–7A/cm2。     

Growth and doping of SiC-thin films on low-stress,amorphous Si<Subscript>3</Subscript>N<Subscript>4</Subscript>/Si substrates for robust microelectromechanical systems applications

The N₂-doped 3C-SiC thin films have been grown by low-pressure, chemical vapor deposition (LPCVD) on amorphous Si₃N₄/p-Si (111) substrates using the single, organosilane-precursor trimethylsilane [(CH₃)₃SiH]. The effects of N₂ flow rate and growth temperature on the electrical properties of SiC films were investigated by Hall-effect measurements. The electron-carrier concentration is between 10¹⁷–10¹⁸/cm³. The lowest resistivities at 400 K and 300 K are 1.12×10⁻² and 1.18×10⁻¹ cm, respectively. The corresponding sheet resistances are 75.02 Ω/□ and 790.36 Ω/□. The SiC film structure was studied by x-ray diffraction. The 3C-SiC films oriented in the 〈111〉 direction with a 2ϑ peak at 35.5° and line widths between 0.18–0.25° were obtained. The SiC/Si₃N₄ interface is very smooth and free of voids. The fabrication of microelectromechanical (MEMS) structures incorporating the SiC films is discussed.     

Photoemission (XPS and XPD) study of epitaxial LaAlO3 film grown on SrTiO3(0 0 1)

This study investigates the tensile-strained growth of LaAlO₃ on SrTiO₃(0 0 1) substrate by molecular beam epitaxy (MBE). Growth was controlled in situ by reflection high energy electron diffraction (RHEED). The characterization was carried out ex situ by photoemission and atomic force microscopy (AFM). Photoelectron spectroscopy (XPS) reveals the development of a TiO_x-rich interface. Photoelectron diffraction (XPD) confirms that a 1.2-nm-thick pseudomorphic LaAlO₃ film has been grown on SrTiO₃(0 0 1) substrate with a perpendicular lattice parameter of 0.372±0.02 nm.     

Effects of PCBM concentration on the electrical properties of the Au/P3HT:PCBM/n-Si (MPS) Schottky barrier diodes

In this study, the gold/poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester/n-type silicon (Au/P3HT:PCBM/n-Si) metal–polymer–semiconductor (MPS) Schottky barrier diodes (SBDs) were investigated in terms of the effects of PCBM concentration on the electrical parameters. The forward and reverse bias current–voltage (I–V) characteristics of the Au/P3HT:PCBM/n-Si MPS SBDs fabricated by using the different P3HT:PCBM mass ratios were studied in the dark, at room temperature. The main electrical parameters, such as ideality factor (n), barrier height (Φ_B0), series resistance (R_s), shunt resistance (R_sh), and density of interface states (N_ss) were determined from I–V characteristics for the different P3HT:PCBM mass ratios (2:1, 6:1 and 10:1) used diodes. The values of n, R_s, Φ_B0, and N_ss were reduced, while the carrier mobility and current were increased, by increasing the PCBM concentration in the P3HT:PCBM organic blend layer. The ideal values of electrical parameters were obtained for 2:1 P3HT:PCBM mass ratio used diode. This shows that the electrical properties of MPS diodes strongly depend on the PCBM concentration of the P3HT:PCBM organic layer. Moreover, increasing the PCBM concentration in P3HT:PCBM organic blend layer improves the quality of the Au/P3HT:PCBM/n-Si (MPS) SBDs which enables the fabrication of high-quality electronic and optoelectronic devices.     

Sn4+替代Nb5+对Bi2(Zn1/3Nb2/3)2O7陶瓷性能的影响

采用固相反应法制备了Bi2(Zn1/3Nb2/3)2O7(BZN)微波陶瓷,并借助XRD、SEM及LCR4284测试仪,研究了Sn4+取代Nb5+对BZN陶瓷显微结构和介电性能的影响。结果表明:随着Sn4+替代量的增加,微观形貌中出现棒晶;选取20～80℃,100 kHz时的εr计算,介电常数温度系数由205×10–6/℃逐渐减小到–240×10–6/℃;当替代量x(Sn4+)为0.16时,样品出现介电弛豫现象;随着测试频率的增加,介电弛豫峰向高温移动。