Hopping Carrier Research Articles

Extracting charge carrier mobility in organic solar cells through space-charge-limited current measurements

Mobility is a critical parameter influencing the overall performance of organic solar cells (OSCs). Herein, we innovatively elucidated the intricate interrelation between the photovoltaic molecular structures and the methodologies employed for the extraction of charge carrier mobility in OSCs. We proposed a simple yet effective principle to accurately extract charge carrier mobility values using the standard space-charge-limited current (SCLC) measurement, while critically assessing theoretical and experimental deficiencies through the drift-diffusion analysis. It was found that field-dependent charge transport is necessitated to describe the prominent long-range intrachain hopping carrier behavior in polymers, while short-range intermolecular hopping results in trap-involved charge transport within small molecular acceptors. Based on the above understanding, a synergetic inter/intra-molecular hopping strategy was proposed to fabricate thick-film all-polymer OSCs, and an unprecedented power conversion efficiency (PCE) of 16.61 % was achieved in the 300 nm PM6:PY-IT OSC. This work not only presents a precise and straightforward approach for measuring mobility values, but also provides a significant reference about charge carrier transport to make optimal decisions regarding photovoltaic material design and device fabrication process of high-performance OSCs.

High-Resolution Wideband Waveform Design for Sonar Based on Multi-Parameter Modulation

The design of transmitting waveforms is an effective way to improve the detection performance of sonar systems. For the problem of high-range sidelobe when designing reverberation-resistant waveforms, this paper proposes a high-resolution wideband composite waveform design with reverberation suppression performance and a waveform parameter improvement method. Firstly, we propose a novel wideband waveform, which utilizes linear frequency modulation (LFM) as the fundamental pulse, referred to as multi-parameter coded modulation LFM pulse (MPCM-LFM). Additionally, we deduce the wideband ambiguity function for waveform design. Then, we deduce the constraint relations of the waveform parameters for different sub-band overlaps, and according to the mathematical expressions of the obtained range ambiguity function, we analyze in detail the effects of the waveform parameters on the range ambiguity function under different constraints. Secondly, on the basis of the analysis, we also propose a hopping carrier frequency constraint rule to optimize the spectral performance, and the range sidelobe is restrained effectively in significant measure by this parameter improvement method. Finally, we analyze the computer simulation results. It is obvious that our proposed waveform parameter improvement method leads to good results. The proposed improved MPCM-LFM signal shows a “near-thumbtack” ambiguity function, whose sidelobe suppression performance is superior to other classical waveforms in the desired region, and it can realize high-precision parameter estimation. In addition, the proposed improved MPCM-LFM signal possesses good performance in detecting stationary and low Doppler targets in the background of reverberation.

Characterization of Effective Mobility and Its Degradation Mechanism in MoS2MOSFETs

Effective mobility in top-gated MoS 2 metal-oxide-semiconductor field-effect transistors (MOSFETs) with HfO 2 /TaN gates was investigated. We propose a model for effective mobility in MoS 2 MOSFETs and discuss its usefulness. Parameter fitting of the proposed effective mobility model makes possible a discussion of how the scattering mechanism limits the effective mobility. Charged impurities, phonons, and surface roughness were presumed to be possible causes of scattering, and the effect of contact resistance was also taken into account. In the device exhibiting the better mobility of 17.4 cm 2 /Vs, phonon-assisted hopping carrier transport probably limited the mobility. In contrast, in the device exhibiting the worse mobility of 2.8 cm 2 /Vs, scattering caused by charged impurities dominated the transport characteristics. The proposed model facilitates device-to-device comparisons of carrier transport characteristics of MoS 2 transistors at room temperature and accelerates their further development.

Analysis of applicability of the transport level concept in organic materials, providing correlated disorder

Investigations of charge transport in disordered organic materials are actively developing area of science today. We investigated hopping carrier transport in disordered organic materials according to the model of correlated disorder (namely, the model of dipole glass). Numerical Monte-Carlo simulation of a random walk of charge after it's jump from deep localized state was performed. The applicability of transport level concept was held.

Electrical Conductivity of V2O5–TeO2–Sb Glasses at Low Temperatures

Semiconducting glasses of the type 40TeO2–(60 − x) V2O5–xSb were prepared by rapid melt quenching and their dc electrical conductivity was measured in the temperature range 180–296 K. For these glassy samples, the dc electrical conductivity ranged from 2.26 × 10−7 S cm−1 to 1.11 × 10−5 S cm−1 at 296 K, indicating the conductivity is enhanced by increasing the V2O5 content. These experimental results could be explained on the basis of different mechanisms (based on polaron-hopping theory) in the different temperature regions. At temperatures above ΘD/2 (where ΘD is the Debye temperature), the non-adiabatic small polaron hopping (NASPH) model is consistent with the data, whereas at temperatures below ΘD/2, a T−1/4 dependence of the conductivity indicative of the variable range hopping (VRH) mechanism is dominant. For all these glasses crossover from SPH to VRH conduction was observed at a characteristic temperature TR ≤ ΘD/2. In this study, the hopping carrier density and carrier mobility were determined at different temperatures. N (EF), the density of states at (or near) the Fermi level, was also determined from the Mott variables; the results were dependent on V2O5 content.

Design of a full-band CMOS UWB receiver and fast-hopping carrier generator for 3.1–10.6 GHz

This paper presents an interference rejection full-band UWB receiver and fast hopping carrier generator for 3.1---10.6 GHz. This receiver enables 11 bands of operation by embedding a tunable notch filter to eliminate interferers in a 5 GHz wireless local area network. The carrier generator can cover 3.1---10.6 GHz within less than 9.5 ns. The receiver, based on the proposed multi-band OFDM standard, consists of a zero-IF receive chain and required system noise figure, the receiver linearity specifications of which are discussed in this paper. It consists of a single-ended low-noise amplifier (LNA), a down-conversion mixer, a low-pass filter (LPF), and a programmable gain amplifier with an IO buffer. The LNA employs a common-gate topology of the 1st stage with dual-resonant loads, a cascade amplifier of the 2nd stage for mid-band resonance, and a tunable notch filter. The down-conversion mixer adopts a single-balanced architecture with LO cancellation. The LPF is implemented based on an active RC topology, and implements a four-stage programmable gain amplifier. The receiver dissipates 49.3 mA from a 1.8 V power supply. The average voltage conversion gain of the receiver IC is 73.5 dB, and the system noise figure is 8.4 dB. Input P1dB increases from ?36.8 dBm at 4 GHz to ?30.5 dBm at 10.3 GHz. The attenuation is 8.5 dB, which is achieved in the interference rejection band at 5.2 GHz. It occupies an area of 0.98 × 3.3 mm2 including the bond pads.

Ferroelectricity in the glassy material of the composition Bi 2O 3–Pb 3O 4–CuO–K 2O

Glass sample of the composition 31.4 Bi 2O 3–2.33 Pb 3O 4–64.53 CuO–1.74 K 2O in mol% was prepared by the conventional quenching melt technique. The as-quenched single phase glass shows interesting ferroelectric properties which is not known in the field of glass science. If the as-quenched glass is heat treated above the glass transition temperature all signs of ferroelectricity disappears completely. X-ray diffraction and transmission electron microscopy as well as differential thermal analysis were used to recognize the glassy nature of the as-quenched sample. Ac dielectric measurements were performed as a function of temperature and frequency and showing ferroelectric to paraelectric phase transition at Curie's temperature of 540 K. Non-linear polarization as a function of temperature and applied electric field as well as pyroelectricity were also studied. The conduction mechanism was confirmed to obey the adiabatic small polaron hopping (SPH) and was mainly due to electronic transport between Cu ions. The dominant factor determining conductivity was the hopping carrier mobility in this glass. From the best fits, reasonable values of various SPH and VRH parameters are obtained.

Structure and electrophysical properties of a lead iron niobate-based amorphous material

An amorphous material based on lead iron niobate (PFN) is studied by X-ray diffraction and dielectric and Mossbauer measurements over a wide temperature range. The atomic structure of amorphous PFN is found to be substantially disordered, which suppresses the transitions into ordered states in the electric and magnetic dipole subsystems that are inherent in crystalline PFN. The dependence of electrical conductivity σ on field frequency ω is shown to correspond to the law σ ∼ ω s , where parameter s decreases linearly with increasing temperature. This law corresponds to a hopping carrier transfer mechanism that is correlated due to the Coulomb interaction.

Structural and Polaronic transport properties of semiconducting CuO–V 2O 5–TeO 2 glasses

Ternary semiconducting glasses in the CuO–V 2O 5–TeO 2 system have prepared by the press-quenching technique. X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimeter (DSC), infrared (IR) spectra, density ( d) and oxygen molar volume ( V m) and dc conductivity ( σ) of these glasses were reported. The overall features of XRD curves confirm the amorphous nature of the present glasses. SEM exhibits a surface without any presence of microstructure which is a characteristic of the amorphous phase. Density was observed to decrease with an increase in V 2O 5 content. The network structure for the glass compositions with 57.5 mol% V 2O 5 is built up of the VO 5 polyhedra, while the other glass compositions consist of VO 4 polyhedra. The temperature dependence of the conductivity data has been analyzed in terms of different polaronic models. In high-temperature region above θ D/2 the Mott model of SPH between nearest neighbors is consistent with the conductivity data, while at intermediate temperature the Greaves VRH (variable-range hopping) model was found to be appropriate. The conduction was confirmed to obey the adiabatic SPH and was mainly due to electronic transport between V ions. The dominant factor determining conductivity was the hopping carrier mobility in these glasses.

Field-effect transistors with thin films of perylene on SiO2 and polyimide gate insulators

Field-effect transistor (FET) devices have been fabricated with thin films of perylene on SiO2 and polyimide gate insulators, and p-channel FET properties have been found in both FET devices. The perylene FET devices with SiO2 and polyimide gate insulators exhibited field-effect mobility, μ, values of 7.0×10−3 and 3.7×10−4cm2V−1s−1, respectively, at 300K under vacuum of 10−6Torr. These FET devices were found to operate under atmospheric condition after exposure to air. The μ value increased with increasing temperature from 160to280K, showing a hopping carrier transport.

A 6.3-9-GHz CMOS fast settling PLL for MB-OFDM UWB applications

A CMOS phase-locked loop (PLL) which synthesizes frequencies between 6.336 and 8.976 GHz in steps of 528 MHz and settles in approximately 150 ns is presented. The proposed PLL can be employed as a building block for a frequency synthesizer which generates a seven-band hopping carrier for multiband orthogonal frequency division multiplexing (MB-OFDM) ultrawideband (UWB) radio. To achieve fast loop settling, integer-N architecture that operates with 528-MHz reference frequency is implemented and a wideband active-loop filter is integrated. An improved phase-frequency detector (PFD) is proposed for faster loop settling. To reduce reference sidebands, a feedback circuit using replica bias is implemented in the charge pump. I/Q carriers are generated by two cross-coupled LC VCOs. The output current of the charge pump is controlled to compensate for the VCO gain nonlinearity and a programmable frequency divider (12/spl les/N/spl les/17) that reliably operates at 9 GHz is designed. Fabricated in 0.18-/spl mu/m CMOS technology, the PLL consumes 32 mA from a 1.8-V supply and achieves phase noise of -109.6dBc/Hz at 1-MHz offset and spurs of -52 dBc.

The frequency-hopped Cartesian feedback linear transmitter

A frequency-hopped version of the Cartesian feedback linear transmitter for use in future mobile communication systems is introduced. The essential requirements for the successful operation of such a transmitter are discussed. Using the results obtained from a hardware prototype, the problems generated by a hopping carrier are outlined and solutions introduced.

Polarization in hopping transport

This paper discusses the possibility of a hopping carrier giving rise to dielectric absorption. It is conjectured that the dielectric absorption in amorphous materials should be attributed to correlation between jumps of the carriers. In the simplified model proposed, the carrier, after arriving at a given lattice site, may choose between subsites, this limited degree of freedom leading to a polarization process in the presence of an electric field. This polarization is discontinued when the particle makes a jump to a new lattice site, where the polarization is relaxed. The Debye relaxation law is obtained as a limiting case.