Capacitance-frequency Characteristics Research Articles

Mercury-probe measurement of electron mobility in β-Ga2O3 using junction moderated dielectric relaxation

We demonstrate the junction-moderated dielectric relaxation method to measure the in-plane electron mobility in β-Ga2O3 epitaxial layers. Unlike the Hall technique and channel mobility measurement in field-effect transistors, this method does not require the deposition of permanent metal contacts. Rather, it measures the bias voltage and frequency dependence of the equivalent capacitance of the Mercury/β-Ga2O3/Mercury structure consisting of a Schottky contact, a quasi-neutral thin film semiconductor, and an Ohmic contact connected in series. The intrinsic dielectric relaxation of the bulk β-Ga2O3 semiconductor typically occurs at ∼1012 s−1, but when moderated by the Mercury/β-Ga2O3 Schottky junction, it manifests itself as an inflection in the capacitance-frequency characteristics at a much lower frequency of ∼106 s−1 within the range of most capacitance measuring instruments. Using carrier density and layer thickness determined from capacitance-voltage measurement, we extract the electron mobility of β-Ga2O3 from the junction-moderated dielectric relaxation frequency.

Voltage-frequency dependence of the complex dielectric and electric modulus and the determination of the interface-state density distribution from the capacitance-frequency measurements of Al/p-Si/Al and Al/V2O5/p-Si/Al structures

The energy distribution of the interface states (Nss) and relaxation time (τ) are calculated from the capacitance-frequency (C-f) characteristics for Al/p-type Si/Al metal-semiconductor and Al/V2O5/p-type Si/Al metal–interfacial layer–semiconductor diodes with and without anodic surface passivation. The experimental results show that the density of the interface states and the relaxation times increase almost exponentially with the bias from the top of the valence band to the center of the gap for each diode produced. At the same time, using the C-f characteristics, the dielectric properties such as the dielectric constant (ε′), dielectric loss (ε″), dielectric loss tangent (tanδ), real and imaginary portions of the electric modulus (M’ and M″) and ac electrical conductivity (σac) are investigated in this study. The analysis was performed at room temperature, in the frequency range from 1 kHz to 10 MHz, and the voltage range from 0 to 0.24 V. The experimental results show that the ε′, ε″ and tanδ values decrease with increasing frequency while σac, M′ and M″ values increase. This results will show that dielectric parameters are strongly frequency dependent.

Evaluation of Industrial Poly(tert-butyl acrylate) insulated A p-channel Organic Field-Effect Transistor (PtBA-p-OFET)

Poly(tert-butyl acrylate) (PTB-p-A) has been investigated as a promising insulator layer for p-channel organic field effect transistors (p-OFETs) using the p-type semiconductor Poly(3-hexylthiophene-2,5-diyl (P3HT) due to its favorable insulating properties, good film-forming ability and electrical charge separation properties. Top-gate, bottom-contact PTBA-p-OFET devices are fabricated with Indium Thin Oxide (ITO) source/drain electrodes and a P3HT organic semiconductor layer. The frequency-dependent capacitance of the PTBA-p-OFETs was studied through a plot to determine the key parameters, including the threshold voltage (VTh), field-effect mobility (μFET), and the current on/off ratio (Ion/off) of the device. The PTB-p- OFETs exhibit field-effect mobility value of 6.13x10-4 (cm2/V.s), an on/off current ratio of 1.11x102, and a threshold voltage of -15.8 V. The capacitance-frequency characteristics of the capacitor structure were analyzed and found to have as 7.6 nF/cm2 per unit area. This work presents PTBA as a promising for high-performance p-OFET applications.

Peculiarities of Electric and Dielectric Behavior of Ni- or Fe-Doped ZnO Thin Films Deposited by Atomic Layer Deposition.

The physical properties of ZnO can be tuned efficiently and controllably by doping with the proper element. Doping of ZnO thin films with 3D transition metals that have unpaired electron spins (e.g., Fe, Co, Ni, etc.) is of particular interest as it may enable magnetic phenomena in the layers. Atomic layer deposition (ALD) is the most advanced technique, which ensures high accuracy throughout the deposition process, producing uniform films with controllable composition and thickness, forming smooth and sharp interfaces. In this work, ALD was used to prepare Ni- or Fe-doped ZnO thin films. The dielectric and electrical properties of the films were studied by measuring the standard current-voltage (I-V), capacitance-voltage (C-V), and capacitance-frequency (C-f) characteristics at different temperatures. Spectral ellipsometry was used to assess the optical bandgap of the layers. We established that the dopant strongly affects the electric and dielectric behavior of the layers. The results provide evidence that different polarization mechanisms dominate the dielectric response of Ni- and Fe-doped films.

Performance analysis of un-doped and doped titania (TiO ) as an electron transport layer (ETL) for perovskite solar cells.

Density functional theory (DFT) calculations are carried out on pure and doped rutile TiO . The bandgap (E ) for pristine, S-doped, Fe-doped, and Fe/S co-doped materials is direct, with values of 2.98 eV, 2.18 eV, 1.58 eV, and 1.40 eV. The effective mass of charge carriers (m*) and ratio of effective masses of holes to effective masses of electrons (R) are also investigated, and it is discovered that Fe/S co-doped materials have the lowest charge carrier recombination rate. The Fe/S co-doped material has the highest . of doped materials shifted into the visible range. Due to the high dopant concentration in Fe and Fe/S-doped cases, the E is lowered to a relatively small value; hence, only pristine and S-doped materials are verified as electron transport layer (ETL). A solar cell device analysis employing pure and S-doped rutile TiO as ETL is completed using DFT-derived parameters in SCAPS-1D modeling software for the first time. For the optimized solar cells, current-voltage (IV) characteristics, quantum efficiency (QE), capacitance-voltage (CV) characteristics, and capacitance-frequency (Cf) characteristics are provided. The aim of the present study is to improve efficiency of perovskite solar cell by doping as well as to improve accuracy of simulation by applying DFT extracted parameters as input. From the analysis, improvement is found in efficiency of doped TiO compared to un-doped TiO . The efficiency of the PSC with S-doped ETL is 1.418% higher than the PSC with un-doped ETL. Quantumwise Automistic Tool Kit (ATK) is used to extract DFT parameters. Using these DFT parameters as input in SCAPS-1D (Solar Cell Capacitance Simulator), solar cells for doped and un-doped material are simulated. The density functional theory (DFT)-based orthogonalized linear combination of atomic orbital (OLCAO) technique is used. Structural optimization is done using the LBFGS (Limited-memory Broyden-Fletcher-Goldfarb-Shanno). PBESol-GGA (Perdew-Burke-Ernzerhof solid-generalized gradient approximation) is applied as exchange correlation for calculating structural parameters, while MGGA-TB09 (meta-generalized gradient approximation-Tran and Blaha) is applied as exchange correlation for calculating optical and electronic properties.

Analysis of the characteristics of organic light-emitting diodes with single and mixed-host EML by impedance spectroscopy

Impedance spectroscopy was used to investigate the charge transportation and accumulation mechanisms in a mixed-host emissive layer (EML) of phosphorescent organic light-emitting diodes (OLEDs). 1, 3, 5-tris(1-phenyl-1H-benzimidazole-2-yl)benzene (TPBi) and 4, 4′, 4″-tris(N-carbazolyl)-triphenylamine (TCTA) materials were used as the electron transport and hole transport layers, respectively, to fabricate the mixed-host EML device. The results showed enhanced current and power efficiency owing to the use of the same material as the mixed-host EML, eliminating energy barriers within the device, coupled with the negative interfacial charges in the polarized TPBi material. The hole- and electron-split devices of the mixed-host EML OLED were analyzed to comprehensively understand the enhanced electrical properties within the device. Subsequently, the capacitance-frequency (C–F) characteristics of the devices were simulated with an equivalent circuit to quantitatively determine the capacitance and resistance in each organic layer at specific voltages (0–4 V) representing each characteristic step on the capacitance-voltage (C–V) curve.

Enhanced Synaptic Properties in Biocompatible Casein Electrolyte via Microwave-Assisted Efficient Solution Synthesis

In this study, we fabricated an electric double-layer transistor (EDLT), a synaptic device, by preparing a casein biopolymer electrolyte solution using an efficient microwave-assisted synthesis to replace the conventional heating (heat stirrer) synthesis. Microwave irradiation (MWI) is more efficient in transferring energy to materials than heat stirrer, which significantly reduces the preparation time for casein electrolytes. The capacitance-frequency characteristics of metal-insulator-metal configurations applying the casein electrolyte prepared through MWI or a heat stirrer were measured. The capacitance of the MWI synthetic casein was 3.58 μF/cm2 at 1 Hz, which was higher than that of the heat stirrer (1.78 μF/cm2), confirming a stronger EDL gating effect. Electrolyte-gated EDLTs using two different casein electrolytes as gate-insulating films were fabricated. The MWI synthetic casein exhibited superior EDLT electrical characteristics compared to the heat stirrer. Meanwhile, essential synaptic functions, including excitatory post-synaptic current, paired-pulse facilitation, signal filtering, and potentiation/depression, were successfully demonstrated in both EDLTs. However, MWI synthetic casein electrolyte-gated EDLT showed higher synaptic facilitation than the heat stirrer. Furthermore, we performed an MNIST handwritten-digit-recognition task using a multilayer artificial neural network and MWI synthetic casein EDLT achieved a higher recognition rate of 91.24%. The results suggest that microwave-assisted casein solution synthesis is an effective method for realizing biocompatible neuromorphic systems.

Electric characterization of transition metal (Co, Ni, Fe) doped ZnO thin layers prepared by atomic layer deposition

Doping of ZnO with different ions enables efficient control of its optical, electrical and magnetic properties. ZnO thin films doped with 3d transition metals have potential to be used as diluted magnetic semiconductors. In this work, dielectric and electrical properties of transition metal (Ni-, Co- or Fe-) doped ZnO thin films prepared by atomic layer deposition (ALD) have been studied. Standard capacitance-voltage (C-V) and current-voltage (I-V) as well as capacitance-frequency (C-f) characteristics have been measured. Some important parameters, e.g. the concentration of majority carriers N D, barrier height Ф b as well as the built-in potential Vbi are determined. Different polarization effects are considered to explain the strong frequency dependence of dielectric constant.

Comparison of capacitance-frequency and current-voltage characteristics of Al/CdS-PVP/p-Si and Al/p-Si structures

In this paper, we report a simple ultrasound-assisted method for the preparation of CdS nanostructures to utilize as an interfacial layer for fabrication of Al/CdS-PVP/p-Si structure. The comparison of C-f and I–V characterizations on both Al/p-Si (MS) and Al/CdS-PVP/p-Si (MPS) Schottky structures have been analyzed and reported. For the fabrication of CdS semiconductor nanostructures, the sonochemistry method was used. The optical, compositional, and structure of the prepared CdS nanostructures have been investigated by UV–Vis spectroscopy, X-ray diffraction (XRD), FE-SEM, and EDX techniques. The main electrical and dielectric parameters of the fabricated MS and MPS structures have been characterized. The analyses depict the presence of CdS-PVP nanocomposite improves the efficiency of the MPS diode by reducing the ideality factor and increasing the barrier height and shunt resistance. The result of dielectric studies showed dielectric parameters are strongly frequency-dependent.

Computational analysis of bandgap tuning, admittance and impedance spectroscopy measurements in lead‐free MASnI 3 perovskite solar cell device

Recently, lead-free perovskite solar cell (PSC) heterostructure using CH3NH3SnI3 (MASnI3) absorber layer received significant attention due to their superior device performance. However, the effect of deep defect state on device performance is only little known about the MASnI3 absorber based PSC. In the present study, initially we optimized the power conversion efficiency of the device via the bandgap tuning and electron affinity variations in MASnI3 absorber layer using SCAPS-1D simulator. Thereafter, the capacitance-voltage (C-V), Mott-Shottkey (MS) (1/C2-V) and conductance-voltage (G-V) measurements are performed through simulation approach, which confirmed a solid sign of deep defects in the perovskite heterostructure device. In addition, temperature dependent capacitance-frequency (C-f) characteristics confirmed the clear expectancy of thermally-induced variations in capacitance (or dielectric constant) under illumination and dark, respectively. Further, supremacy of the space charge region in MASnI3 based PSC is confirmed from the voltage dependent semicircular nature of the Nyquist plots. Shrink in the semicircles of the Nyquist plots with the increase of the forward bias voltage also confirm the improvement of carriers under forward bias which increase the conductivity and therefore decrease the impedance.

Low density of interface trap states and temperature dependence study of Ga2O3 Schottky barrier diode with p-NiOx termination

This work acquires a vertical β-Ga2O3 Schottky barrier diode (SBD) with the advanced termination structure of p-type NiOx and n-type β-Ga2O3 heterojunctions and coupled field plate structures to alleviate the crowding electric field. A Ga2O3 SBD delivers an average breakdown voltage of 1860 V and a specific on-resistance of 3.12 mΩ cm2, yielding a state-of-the-art direct-current Baliga's power figure of merit of 1.11 GW/cm2 at an anode area of 2.83 × 10−5 cm2. In addition, the Ga2O3 SBD with the same fabrication process at a large area of 1.21 × 10−2 cm2 also presents a high forward current of 7.13 A, a breakdown voltage of 1260 V, and a power figure-of-merit of 235 MW/cm2. According to dynamic pulse switching and capacitance-frequency characteristics, an optimized p-NiOx/Ga2O3 interface with a maximum trap density of 4.13 × 1010 eV−1 cm−2 is delivered. Moreover, based on the forward current-voltage measurement at various temperatures, the physics behind a forward conduction mechanism is illustrated. Ga2O3 SBDs with p-NiOx/n-Ga2O3 heterojunction termination, field plate, high power figure of merit, and high quality interface as well as suppressed resistance increase after dynamic pulse switching, verifying their great promise for future high power applications.

Effect of pore size in activated carbon on the response characteristic of electric double layer capacitor

The effect of pore size on the response characteristic of an electric double layer capacitor (EDLC) was closely examined. A series of phenol-resin-based activated carbon (AC) samples was prepared as average pore size from 0.94 to 1.68 nm by KOH activation by varying the activation temperature and KOH/carbonized phenol-resin ratio. The impedance properties of pouch-type EDLC cells prepared using AC samples were evaluated by applying an alternating current at 3 V between 10 mHz and 100 kHz for confirming the response characteristic. The cell based on the AC with a largest pore size (1.68 nm) showed fast response frequency, and had a high dielectric relaxation time constant as calculated from the response frequency value. The AC with the largest pore size, which consisted of both micropores (>1 nm) and mesopores (2–4 nm), was confirmed to facilitate extremely low electrolyte-diffusion resistance during the formation of the electric double layer, implying that the large pores lead to fast and stable response frequency. The presented findings suggest that AC with a largest pore size as the electrode leads to superior capacitance and response frequency characteristics in the alternating current than those of an AC with a smaller pore size.

Degradation analysis of doped organic p-n heterojunction charge generation layers by impedance and optical spectroscopy

Investigation of the long-term stability of charge generation layers (CGLs) provides a fundamental and an essential approach in achieving highly efficient tandem organic electronic devices. Thus, in this foremost study, the degradation mechanism of electrically aged organic p-n heterojunction CGLs has been investigated by impedance and optical spectroscopy. Rubidium carbonate (Rb2CO3)–doped 2,2,2-(1,3,5-benzinetriyl)-tris(1-phenyl-1H-benzimidazole) (TPBi) and molybdenum trioxide (MoO3)–doped 1,4-bis[N-(1-naphthyl)-N′-phenylamino]-4,4′-diamine (NPB) are used as the n-type and p-type organic semiconductors, respectively. A detailed analysis from capacitance-frequency (C–F) and capacitance-voltage (C–V) characteristics reveals reduced charge generation and 19.6% reduction in the geometric capacitance of the CGL after electrical aging. Reduced peak intensity from UV–Vis–NIR spectra of the aged CGL points to 21.4% charge transfer complex decomposition of the Rb2CO3-doped TPBi. We propose that the rate-limiting step of charge generation in the CGL is caused by the electron transport in the TPBi:Rb2CO3 layer and not the charge generation itself at the TPBi:Rb2CO3/NPB:MoO3 heterojunction. This simple, comprehensive, and non-destructive technique facilitates a crucial analysis that underpins the mechanism of device degradation and further provides a fundamental approach in developing highly stable CGLs for efficient organic electronic devices.

Determination of trap density-of-states distribution of nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite films

Thin films comprising nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous-carbon (UNCD/a-C:H) composite films were experimentally investigated. The prepared films were grown on Si substrates by the coaxial arc plasma deposition method. They were characterized by temperature-dependent capacitance-frequency measurements in the temperature and frequency ranges of 300–400 K and 50 kHz–2 MHz, respectively. The energy distribution of trap density of states in the films was extracted using a simple technique utilizing the measured capacitance-frequency characteristics. In the measured temperature range, the energy-distributed traps exhibited Gaussian-distributed states with peak values lie in the range: 2.84 × 1016–2.73 × 1017 eV–1cm–3 and centered at energies of 120–233 meV below the conduction band. These states are generated due to a large amount of sp2-C and π-bond states, localized in GBs of the UNCD/a-C:H film. The attained defect parameters are accommodating to understand basic electrical properties of UNCD/a-C:H composite and can be adopted to suppress defects in the UNCD-based materials.

High-quality remote plasma enhanced atomic layer deposition of aluminum oxide thin films for nanoelectronics applications

Here, we report comprehensive investigations of aluminum oxide (Al2O3) high-κ gate oxides deposited via remote plasma enhanced atomic layer deposition (Re-PEALD) with mesh configuration in a commercial 100 mm ALD reactor. Trimethylaluminum (Al(CH3)3), dioxygen (O2) plasma, and Argon (Ar) are used as the metal precursor, oxidant, and carrier/purge, respectively. The growth rate per cycle and non-uniformity of Al2O3 thin films is analyzed with the variation in duration of (Al(CH3)3) pulse, O2 plasma, post-precursor purge, post-oxidant purge, RF power, and substrate temperature. High-quality monolayer type Al2O3 thin films with a growth rate of ~ 1.1 Å/cycle are achieved for a wide temperature range from ~ 100 °C to ~ 300 °C suitable for various nanoelectronics applications ranging from flexible substrates to low thermal budget and high mobility alternate semiconductor substrates. Further, the Al/Re-PEALD-Al2O3/p-Si, metal-oxide-semiconductor (MOS) structures are investigated for capacitance-voltage, capacitance-frequency, and leakage current-voltage characteristics to demonstrate the quality of Re-PEALD-Al2O3 thin films. The Al/Re-PEALD-Al2O3/p-Si, MOS structures revealed excellent electrical characteristics with ultralow minimum interface trap density (Dit) ~ 9.9 × 109 eV−1cm−2, negative effective oxide charges (Neff) ~ 5.52 × 1012 cm−2, low leakage current density of ~ 4.1 nA/cm2 at −1 V, hysteresis-free, insignificant Vth shift, and trivial frequency dispersion. Moreover, the chemical analysis using XPS depth profiling disclosed that Re-PEALD deposited Al2O3 thin films results in a high-quality gradient Al2O3/SiOx/Si interface rather than an abrupt Al2O3/Si interface, and the oxygen rich thin films due to the oxygen (O2−) interstitials close to the interface are the sources of negative fixed oxide charges in Re-PEALD-Al2O3/Si, system. These results intend to boost the investigations of Re-PEALD Al2O3 ultrathin films for low thermal budget high mobility alternate semiconductor substrates for nanoelectronics applications.

A Study of the Gate-Stack Small-Signal Model and Determination of Interface Traps in GaN-Based MIS-HEMTs

The existing gate-stack small-signal models of metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) were analyzed, and a new model that could fit the measured admittance characteristics in the whole bias regime after learning about their shortcomings was presented. The capacitance and conductance frequency characteristics were fitted simultaneously, and the extracted fitting parameters showed reasonable values and trends. These parameters were then used in the determination of interface traps as well as the quantitative analysis of two C-V slopes for MIS-HEMTs. It was proven that the intrinsic barrier resistance was also a critical factor for the second slope. Thus, this resistance could not be neglected by the capacitance method that determined the interface trap densities directly by the frequency dispersion of the second slope. This article extracted the energy distribution of the interface trap density, which could be fitted by a Gaussian distribution with a maximum value of ~ 3×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . Although this method was a suitable alternative because the capacitance and conductance were correlated by the admittance characteristics, the detected shallow-level traps may not account for the threshold voltage drift or other reliability problems of MIS-HEMTs.

Determination of defect states and surface photovoltage in PTB7:PC71BM based bulk heterojunction solar cells

Defects formed during the device processing acts as recombination centers and shows adverse effects on the photovoltaic performance of the organic solar cells (OSCs). In this manuscript, a study on the effect of defect states on the characteristics of bulk heterojunction (BHJ) solar cells, consisted of unannealed or thermally annealed active layer (ActL) of PTB7:PC71BM blend, have been performed by using the illumination intensity-dependent current-voltage and frequency dependent impedance spectroscopy measurements. Our results indicate that the photovoltaic performance of devices based on annealed ActL is superior than the bench dried ActL due to thermal annealing induced improvement in the thin film morphology. The measured low-frequency capacitance-voltage (C–V) characteristics under varying illumination intensities show strong dependency on the photoexcitation however, the change in the C–V characteristics is found to be quite different for unannealed and annealed devices. The C–V characteristics are analyzed using the drift-diffusion model to extract the effective built-in voltage (Vbi) and the surface photovoltage as a function of illumination intensity. The capacitance-frequency characteristics under illumination reveal that the change in the capacitance is associated with the photo-induced carrier occupation in the intermixture donor-acceptor phases, which act as the defect states in such devices. Further, it is modeled to quantify the defect states and to demonstrate the importance of thermal annealing for improving the OSCs device performance.

Diffusion of charge carriers in pentacene

The diffusion coefficient (D) of charge carriers in pentacene has been determined independently using current–voltage and capacitance–frequency characteristics of asymmetric metal/pentacene/metal structures. The values of D measured using these two methods are found to be in excellent agreement. D has been estimated using first principles calculations and compared with experimental values. The applicability of the Einstein relation has been examined in organic semiconductors.

Impacts of Minority Charge Carrier Injection on the Negative Capacitance, Steady‐State Current, and Transient Current of a Single‐Layer Organic Semiconductor Device

AbstractSpace charge limited current theory is often used to analyze electrical characteristics of single‐layer organic semiconductor devices using Ohmic and Schottky contacts for injection of majority and minority carriers, respectively. However, significant deviations from this theory in the current density–voltage and capacitance–frequency characteristics of the devices have been frequently observed. For instance, the increase in current density is not proportional to the voltage‐square and the capacitance becomes negative at low frequencies. Here, it is presented that the minority carriers in a single‐layer device despite a large Schottky barrier give rise to the negative capacitance at low frequencies and the drastic increase in steady‐state current density at high voltages. The leaky electrons at the hole‐dominant device are demonstrated by inserting an electron scavenger layer. The transient current of the device shows the injection and transport properties of electrons by low and dispersive mobility. The negative capacitance of the device at low frequencies is a response of the minority carrier injection. The current density increases drastically at high voltages due to the increasing minority carriers that redistribute the electric field, which is not shown at low voltages. Finally, the device model incorporating minority charge carriers fully describes the electrical characteristics of the device.

Investigation on the mechanism of charge generation in organic heterojunctions: Analysis of I–V and C–V characteristics

Abstract The charge generation mechanism of organic heterojunction (OHJ) consisted of 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN) and different hole transporting materials (HTMs) are studied systematically by current-voltage (I–V) and capacitance-voltage measurements. The analysis of I–V characteristics of the devices based on OHJs at forward and reverse voltages by comparing the thickness of HTM layers finds that a forward and reverse symmetrical I–V curve is observed at thin HTM layers and the forward current becomes larger than the reverse current with the increase of HTM thickness, fully illustrating the effectiveness of OHJ charge generation. Moreover, the I–V characteristics at different temperatures indicate that the efficient charge generation is originated from electron tunneling rather than diffusion. And the C–V and capacitance-frequency (C–F)characteristics further illustrate the highly efficient charge generation ability of OHJs so that the charge density is as high as 4.5 × 1017 cm−3, guaranteeing the high conductivity of OHJs, which is very beneficial to developing highly efficient OLEDs using OHJs as charge injector and generator.