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1.
A study on p-doping of organic wide band gap materials with Molybdenum trioxide using current transport measurements, ultraviolet photoelectron spectroscopy and inverse photoelectron spectroscopy is presented. When MoO3 is co-evaporated with 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl (CBP), a significant increase in conductivity is observed, compared to intrinsic CBP thin films. This increase in conductivity is due to electron transfer from the highest occupied molecular orbital of the host molecules to very low lying unfilled states of embedded Mo3O9 clusters. The energy levels of these clusters are estimated by the energy levels of a neat MoO3 thin film with a work function of 6.86 eV, an electron affinity of 6.7 eV and an ionization energy of 9.68 eV. The Fermi level of MoO3-doped CBP and N,N′-bis(1-naphtyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (α-NPD) thin films rapidly shifts with increasing doping concentration towards the occupied states. Pinning of the Fermi level several 100 meV above the HOMO edge is observed for doping concentrations higher than 2 mol% and is explained in terms of a Gaussian density of HOMO states. We determine a relatively low dopant activation of ~0.5%, which is due to Coulomb-trapping of hole carriers at the ionized dopant sites.  相似文献   

2.
Commercial bipolar junction transistor (2N 2219A, npn) irradiated with 150 MeV Cu11+-ions with fluence of the order 1012 ions cm?2, is studied for radiation induced gain degradation and deep level defects. IV measurements are made to study the gain degradation as a function of ion fluence. The properties such as activation energy, trap concentration and capture cross-section of deep levels are studied by deep level transient spectroscopy (DLTS). Minority carrier trap levels with energies ranging from EC ? 0.164 eV to EC ? 0.695 eV are observed in the base–collector junction of the transistor. Majority carrier trap levels are also observed with energies ranging from EV + 0.203 eV to EV + 0.526 eV. The irradiated transistor is subjected to isothermal and isochronal annealing. The defects are seen to anneal above 350 °C. The defects generated in the base region of the transistor by displacement damage appear to be responsible for transistor gain degradation.  相似文献   

3.
The p-doping effect of the fluorinated fullerene C60 F36 doped into organic thin films of N,N,N′,N′-tetrakis(4-methoxyphenyl)-benzidine (MeO-TPD) of different purification grades is systematically investigated by photoemission spectroscopy. By reducing the molar doping ratio to MR = 2.9 × 10?4, the Fermi-level shift upon doping is resolved in particular at very low doping concentrations. In comparison to four times sublimated MeO-TPD, 5 times more C60F36 molecules have to be doped into unpurified MeO-TPD films to shift the Fermi-level just above its intrinsic position. This finding is discussed in terms of a statistical model, showing that narrow deep hole-trap states are additionally present in the unpurified host material which are hindering an efficient generation of free charge carriers at molar doping ratios below MR = 0.002.  相似文献   

4.
The effects of p-type doping of wide bandgap ambipolar 4,4′-N,N′-dicarbazolebiphenyl (CBP) with WO3 were investigated through detailed electrical device characterization. It was found that, to achieve effective doping for improved hole injection and transport, the doping level should be greater than 20 mol% and the doped layer should be at least 10 nm thick. A large downward shift of the Fermi level in WO3-doped CBP causes band bending and depletion at the doped/undoped CBP interface, resulting in an additional energy barrier which hampers hole transport. Simplified green phosphorescent organic light-emitting diodes (PhOLEDs) with CBP as the hole transport and host material were fabricated. With a WO3-doped hole transport layer, the PhOLEDs attained brightness of 11,163 cd/m2 at 20 mA/cm2, and exhibited an improved reliability under constant-current stressing as compared to undoped PhOLEDs.  相似文献   

5.
We report a solution processed, p-doped film consisting of the organic materials 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine (MTDATA) as the electron donor and 2-(3-(adamantan-1-yl)propyl)-3,5,6-trifluorotetracyanoquinodimethane (F3TCNQ-Adl) as the electron acceptor. UV–vis–NIR absorption spectra identified the presence of a charge transfer complex between the donor and acceptor in the doped films. Field-effect transistors were used to characterize charge transport properties of the films, yielding mobility values. Upon doping, mobility increased and then slightly decreased while carrier concentration increased by two orders of magnitude, which in tandem leads to conductivity increasing from 4 × 10?10 S/cm when undoped to 2 × 10?7 S/cm at 30 mol% F3TCNQ-Adl. The hole density was calculated based on mobility values extracted from OFET data and conductivity values extracted from bulk IV data for the MTDATA: x mol% F3TCNQ-Sdl films. These films were then shown to function as the hole injection/hole transport layer in a phosphorescent blue OLED.  相似文献   

6.
We have fabricated Au/n-Si and Au/PVA:Zn/n-Si Schottky barrier diodes (SBDs) to investigate the effect of organic interfacial layer on the main electrical characteristics. Zn doped poly(vinyl alcohol) (PVA:Zn) was successfully deposited on n-Si substrate by using the electrospinning system and surface morphology of PVA:Zn was presented by SEM images. The current–voltage (I–V) characteristics of these SBDs have been investigated at room temperature. The experimental results show that interfacial layer enhances the device performance in terms of ideality factor (n), zero-bias barrier height (ΦB0), series resistance (Rs), and shunt resistance (Rsh) with values of 1.38, 0.75 eV, 97.64 Ω, and 203 MΩ whereas those of Au/n-Si SBD are found as 1.65, 0.62 eV, 164.15 Ω and 0.597 MΩ, respectively. Also, this interfacial layer at metal/semiconductor (M/S) interface leads to a decrease in the magnitude of leakage current and density of interface states (Nss). The values of Nss range from 1.36×1012 at Ec—0.569 eV to 1.35×1013 eV?1 cm?2 at Ec—0.387 eV for Au/PVA:Zn/n-Si SBD and 3.34×1012 at Ec—0.560 eV to 1.35×1013 eV?1 cm?2 at Ec—0.424 eV for Au/n-Si SBD. The analysis of experimental results reveals that the existence of PVA:Zn interfacial layer improves the performance of such devices.  相似文献   

7.
Energy level alignments at the interface of N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB)/VO2/fluorine-doped tin oxide (FTO) were studied by photoemission spectroscopy. The overall hole injection barrier between FTO and NPB was reduced from 1.38 to 0.59 eV with the insertion of a VO2 hole injection layer. This could allow direct hole injection from FTO to NPB through a shallow valence band of VO2. Surprisingly, VO2 can also act as a charge generation layer due to its small band gap of 0.80 eV. That is, its conduction band is quite close to the Fermi level, and thus electrons can be extracted from the highest occupied molecular orbital (HOMO) of NPB, which is equivalent to hole injection into the NPB HOMO.  相似文献   

8.
Gallium arsenide diodes with and without indium arsenide quantum dots were electron irradiated to investigate radiation induced defects. Baseline and quantum dot gallium arsenide pn-junction diodes were characterized by capacitance–voltage measurements, and deep level transient spectroscopy. Carrier accumulation was observed in the gallium arsenide quantum dot sample at the designed depth for the quantum dots via capacitance–voltage measurements. Prior to irradiation, a defect 0.84 eV below the conduction band (EC – 0.84 eV) was observed in the baseline sample which is consistent with the native EL2 defect seen in gallium arsenide. After 1 MeV electron irradiation three new defects were observed in the baseline sample, labeled as E3 (EC – 0.25 eV), E4 (EC – 0.55 eV), and E5 (EC – 0.76 eV), consistent with literature reports of electron irradiated gallium arsenide. Prior to irradiation, the addition of quantum dots appeared to have introduced defect levels at EC – 0.21, EC – 0.38, and EC – 0.75 eV denoted as QD–DX1, QD–DX2, and QD–EL2 respectively. In the quantum dot sample after 1 MeV electron irradiation, QD–E3 (EC – 0.28 eV), QD–E4 (EC – 0.49 eV), and QD–EL2 (EC – 0.72 eV) defects, similar to the baseline sample, were observed, although the trap density was dissimilar to that of the baseline sample. The quantum dot sample showed a higher density of the QD–E4 defect and a lower density of QD–E3, while the QD–EL2 defect seemed to be unaffected by electron irradiation. These findings suggest that the quantum dot sample may be more radiation tolerant to the E3 defect as compared to the baseline sample.  相似文献   

9.
The degradation of industry-supplied GaN high electron mobility transistors (HEMTs) subjected to accelerated life testing (ALT) is directly related to increases in concentrations of two defects with trap energies of EC-0.57 and EC-0.75 eV. Pulsed I-V measurements and constant drain current deep level transient spectroscopy were employed to evaluate the quantitative impact of each trap. The trap concentration increases were only observed in devices that showed a 1 dB drop in output power and not the result of the ALT itself indicating that these traps and primarily the EC-0.57 eV trap are responsible for the output power degradation. Increases from the EC-0.57 eV level were responsible for 80% of the increased knee walkout while the EC-0.75 eV contributed only 20%. These traps are located in the drain access region, likely in the GaN buffer, and cause increased knee walkout after the application of drain voltage.  相似文献   

10.
We determined some optical and electrical properties of thin gold phthalocyanine films. Calculations were performed in the framework of density functional theory using the full potential linear augmented plane wave method. Studies on the density of states and band structure yielded a bandgap energy (Eg) of approximately 2 eV. Two trap energy levels were observed at 0.9 and 1.3 eV. Analysis of the dielectric function and electric loss function revealed a plasmon oscillation at 1.8 eV. In addition, we determined static refractive index values in the x, y and z directions of n0xx = 2.16, n0yy = 1.66 and n0zz = 2.07. The optical bandgap of gold phthalocyanine was estimated to be 0.97 eV. Calculations revealed strong absorption at 400–700 nm, which compares favorably with experimental results.  相似文献   

11.
《Organic Electronics》2008,9(5):805-808
Efficient top-emitting organic light-emitting diodes were fabricated using copper iodide (CuI) doped 1,4-bis[N-(1-naphthyl)-N′-phenylamino]-4,4′-diamine (NPB) as a hole injection layer and Ir(ppy)3 doped CBP as the emitting layer. CuI doped NPB layer functions as an efficient p-doped hole injection layer and significantly improves hole injection from a silver bottom electrode. The top-emitting device shows high current efficiency of 69 cd/A with Lambertian emission pattern. The enhanced hole injection is originated from the formation of the charge transfer complex between CuI and NPB.  相似文献   

12.
Three 2,2-dicyanovinyl (DCV) end-capped A-π-D-π-A type oligothiophenes (DCV-OTs) containing dithieno[3,2-b:2′,3′-d]silole (DTSi), cyclopenta[1,2-b:3,4-b′]dithiophene (DTCP) or dithieno[3,2-b:2′,3′-d]pyrrole (DTPy) unit as the central donor part, mono-thiophene as the π-conjugation bridge were synthesized. The absorption spectroscopies, cyclic voltammetry of these compounds were characterized. Results showed that all these compounds have intensive absorption band over 500–680 nm with a LUMO energy level around −3.80 eV, which is slightly higher than that of [6,6]phenyl-C61-butyric acid methyl ester (PC61BM, ELUMO = −4.01 eV), but lower than that of poly(3-hexylthiophene) (P3HT, ELUMO = −2.91 eV). Solution processed bulk heterojunction “all-thiophene” solar cells using P3HT as electron donor and the above mentioned oligothiophenes as electron acceptor were fabricated and tested. The highest power conversion efficiency (PCE) of 1.31% was achieved for DTSi-cored compound DTSi(THDCV)2, whereas PTB7:DTSi(THDCV)2 based device showed slightly higher PCE of 1.56%. Electron mobilities of these three compounds were measured to be around 10−5 cm2 V−1 s−1 by space charge limited current method, which is much lower than that of PC61BM, and was considered as one of the reason for the low photovoltaic performance.  相似文献   

13.
《Organic Electronics》2008,9(2):273-278
The authors demonstrate a fluorescent white organic light-emitting device (WOLED) with double emissive layers. The yellow and blue dyes, 5,6,11,12-tetraphenylnaphthacene and N-(4-((E)-2-(6-((E)-4-(diphenylamino)styryl)naphthalen-2-yl)vinyl)phenyl)-N-phenylbenzenamine, are doping into the same conductive host material, N,N′-dicarbazolyl-4-4′-biphenyl). The maximum luminance and power efficiency of the WOLED are 14.6 cd/A and 9.5 lm/W at 0.01 mA/cm2, with the maximum brightness of 20 100 cd/m2 at 17.8 V. The Commission International de L’Éclairage coordinates change slightly from (0.27, 0.37) to (0.28, 0.36), as the applied voltage increases from 6 V to 16 V. The high efficiencies can be attributed to the balance between holes and electrons.  相似文献   

14.
Silver sulfide (Ag2S) thin films have been deposited on glass substrates by t spray pyrolysis using an aqueous solution which contains silver acetate and thiourea as precursors. The depositions were carried out at a substrate temperature of 250 °C. Structural studies by means of X-ray diffraction show that all tin (Sn)-doped Ag2S thin films crystallized in a monoclinic space group with noticeable changes in the crystallites' orientation. The discussion of some structural calculated constants has been made with Sn doping in terms of microhardness measurements. Moreover, the optical analysis via the transmittance, reflectance as well as the photocurrent reveals that the direct band gap energy (Egd) decreases (Egd varies from 2.34 to 2.16 eV) and the indirect band gap energy (Egi) increases (Egi varies from 0.98 to 1.09 eV) slightly as a function of Sn content. Electrical study shows that Sn doping changes the electrical conductivity and proves the thermal activation of electrical conduction.  相似文献   

15.
The energy level alignment and chemical reaction at the interface between the hole injection and transport layers in an organic light-emitting diode (OLED) structure has been studied using in-situ X-ray and ultraviolet photoelectron spectroscopy. The hole injection barrier measured by the positions of the highest occupied molecular orbital (HOMO) for N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1-biphenyl-4,4-diamine (NPB)/indium tin oxide (ITO) was estimated 1.32 eV, while that with a thin WO3 layer inserted between the NPB and ITO was significantly lowered to 0.46 eV. This barrier height reduction is followed by a large work function change which is likely due to the formation of new interface dipole. Upon annealing the WO3 interlayer at 350 °C, the reduction of hole injection barrier height largely disappears. This is attributed to a chemical modification occurring in the WO3 such as oxygen vacancy formation.  相似文献   

16.
《Organic Electronics》2005,6(1):11-20
A relationship between the energy of the highest occupied molecular orbital (HOMO) and the oxidation potential of molecular organic semiconductors is presented. Approximating molecules as dipoles consisting of a positively charged ion core surrounded by an electron cloud, the HOMO energy (EHOMO) is calculated as that required to separate these opposite charges in a neutral organic thin film. Furthermore, an analysis of image charge forces on spherical molecules positioned near a conductive plane formed by the electrode in an electrochemical cell is shown to explain the observed linear relationship between EHOMO and the oxidation potential. The EHOMO’s of a number of organic semiconductors commonly employed in thin film electronic devices were determined by ultraviolet photoemission spectroscopy, and compared to the relative oxidation potential (VCV) measured using pulsed cyclic voltammetry, leading to the relationship EHOMO = −(1.4 ± 0.1) × (qVCV)  (4.6 ± 0.08) eV, consistent with theoretical predictions.  相似文献   

17.
In the present work we have studied the effect of Na on the properties of graded Cu(In1−xGax)Se2 (CIGS) layer. Graded CIGS structures were prepared by chemical spray pyrolysis at a substrate temperature of 350 °C on soda lime glass. Sodium chloride is used as a dopant along with metal (Cu/In/Ga) chlorides and n, n-dimethyl selenourea precursors. The addition of Na exhibited better crystallinity with chalcopyrite phase and an improvement in preferential orientation along the (112) plane. Energy dispersive analysis of X-rays (line/point mapping) revealed a graded nature of the film and percentage incorporation of Na (0.86 at%). Raman studies showed that the film without sodium doping consists of mixed phase of chalcopyrite and CuAu ordering. Influence of sodium showed a remarkable decrease in electrical resistivity (0.49–0.087 Ω cm) as well as an increase in carrier concentration (3.0×1018–2.5×1019 cm−3) compared to the un-doped films. As carrier concentration increased after sodium doping, the band gap shifted from 1.32 eV to 1.20 eV. Activation energies for un-doped and Na doped films from modified Arrhenius plot were calculated to be 0.49 eV and 0.20 eV, respectively. Extremely short carrier lifetimes in the CIGS thin films were measured by a novel, non-destructive, noncontact method (transmission modulated photoconductive decay). Minority carrier lifetimes of graded CIGS layers without and with external Na doping are found to be 3.0 and 5.6 ns, respectively.  相似文献   

18.
《Organic Electronics》2008,9(3):333-338
Effects of doping molybdenum trioxide (MoO3) in N,N′-diphenyl-N,N′-bis(1,1′-biphenyl)-4,4′-diamine (NPB) are studied at various thicknesses of doped layer (25–500 Å) by measuring the current–voltage characteristics, the capacitance–voltage characteristics and the operating lifetime. We formed charge transfer complex of NPB and MoO3 by co-evaporation of both materials to achieve higher charge density, lower operating voltage, and better reliability of devices. These improved performances may be attributed to both bulk and interface properties of the doped layer. The authors demonstrated that the interface effects play more important role in lowering the operating voltage and increasing the lifetime.  相似文献   

19.
The charge conduction properties of a series of iridium-based compounds for phosphorescent organic light-emitting diodes (OLEDs) have been investigated by thin-film transistor (TFT) technique. These compounds include four homoleptic compounds: Ir(ppy)3, Ir(piq)3, Ir(Tpa-py)3, Ir(Cz-py)3, and two heteroleptic compounds Ir(Cz-py)2(acac) and FIrpic. Ir(ppy)3, Ir(piq)3 and FIrpic are commercially available compounds, while Ir(Tpa-py)3, Ir(Cz-py)3 and Ir(Cz-py)2(acac) are specially designed to test their conductivities with respect to the commercial compounds. In neat films, with the exception of FIrpic, all Ir-compounds possess significant hole transporting capabilities, with hole mobilities in the range of about 5 × 10−6–2 × 10−5 cm2 V−1 s−1. FIrpic, however, is non-conducting as revealed by TFT measurements. We further investigate how Ir-compounds modify carrier transport as dopants when they are doped into a phosphorescent host material CBP. The commercial compounds are chosen for the investigation. Small amounts of Ir(ppy)3 and Ir(piq)3 (<10%) behave as hole traps when they are doped into CBP. The hole conduction of the doped CBP films can be reduced by as much as 4 orders of magnitude. Percolating conduction of Ir-compounds occurs when the doping concentrations of the Ir-compounds exceed 10%, and the hole mobilities gradually increase as their values reach those of the neat Ir films. In contrast to Ir(ppy)3 and Ir(piq)3, FIrpic does not participate in hole conduction when it is doped into CBP. The hole mobility decreases monotonically as the concentration of FIrpic increases due to the increase of the average charge hopping distance in CBP.  相似文献   

20.
We make a two-dimensional transient analysis of field-plate AlGaN/GaN high electron mobility transistors (HEMTs) with a Fe-doped semi-insulating buffer layer, which is modeled that as deep levels, only a deep acceptor located above the midgap is included (EC  EDA = 0.5 eV, EC: energy level at the bottom of conduction band, EDA: deep acceptor's energy level). And the results are compared with a case having an undoped semi-insulating buffer layer in which a deep donor above the midgap (EC  EDD = 0.5 eV. EDD: the deep donor's energy level) is considered to compensate a deep acceptor below the midgap (EDA  EV = 0.6 eV, EV: energy level at the top of valence band). It is shown that the drain-current responses when the drain voltage is lowered abruptly are reproduced quite similarly between the two cases with different types of buffer layers, although the time region where the slow current transients occur is a little different. The lags and current collapse are reduced by introducing a field plate. This reduction in lags and current collapse occurs because the deep acceptor's electron trapping is reduced under the gate region in the buffer layer. The dependence of drain lag, gate lag and current collapse on the field-plate length and the SiN layer thickness is also studied, indicating that the rates of drain lag, gate lag and current collapse are quantitatively quite similar between the two cases with different types of buffer layers when the deep-acceptor densities are the same.  相似文献   

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