Electrical Carrier Transport Research Articles

Effective carrier transport tuning of CuOx quantum dots hole interfacial layer for high-performance inverted perovskite solar cell

Interfacial layer is deemed as an efficient approach to align the energy level and reduce the carrier recombination at the interfaces. Therefore, for the first time, a facile yet effective method to enhance carrier transport by copper oxide quantum dots (CuOx QDs) interfacial layer in inverted perovskite solar cells (PSCs) is developed. The high mobility of CuOx QDs interfacial layer could boost the performance of PSCs by providing a better electrical carrier transport. Furthermore, the higher crystallinity of perovskite layer on CuOx QDs layer reduced the charge trap state densities, which leads to an increase in carrier recombination resistance. As a result, our inverted PSCs exhibit a power conversion efficiency (PCE) of 19.91%, a 14.6% increment compared with the PCE of a control device. Our finding demonstrates the promise of enhancing carrier transport by interfacial layer for high-performance PSCs and expands choice of interfacial layer materials in PSCs.

Correlation between Hall Mobility and Optical Mobility in Aluminum‐Doped ZnO Films via Boundary Scatterings and Estimation of Donor Compensation Ratio

A correlation between the Hall and optical mobility via boundary (BND) scatterings arising from grain as well as surface boundaries in radio frequency (RF) sputtered Al‐doped ZnO (AZO) films done by a comprehensive study on the electrical carrier transport and near infrared optical transmittance properties. AZO films with thicknesses from 100 to 1550 nm are grown by sputtering 1.9 wt% Al2O3‐doped ceramic target under identical growth conditions. The Hall measurement shows an increase in the carrier concentration value from 6.93 × 1020 to 1.1 × 1021 cm−3 with a mobility value (μHall) in the range of 4.98–10.3 cm2 (V s)−1 as the thickness increases. Unprecedentedly, it is shown that the optical mobility value (μopt) calculated using Drude theory is higher than that of the μHall up to a film thickness of ≈1000 nm beyond which both the values merges. Though the carrier concentration is higher than 5 × 1020 cm−3, BND scattering playing an important role in addition to the in‐grain scattering below a thickness of ≈1000 nm is demonstrated. Considering the BND scattering, donor compensation ratio is calculated and is uniquely found to vary with the film thickness.

Carrier transport behavior in as-deposited and iodine-doped plasma polymerized 2, 6-diethylaniline thin films

The temperature dependent electrical carrier transport properties of as-deposited and iodine-doped plasma polymerized 2, 6-diethylaniline (PPDEA) thin films of different thicknesses prepared using a capacitively coupled glow discharge reactor at room temperature were investigated. The FTIR analyses show that iodine doping process occurred at the quinoid units in the polyaniline backbone of PPDEA. The activation energy (ΔE) of both types of PPDEA thin films suggests hopping type conduction of carriers between the localized states at temperatures ranging from 298 K to 423 K. The ΔE in the higher temperature region suggests a thermally activated charge carrier transition mechanism in the energy band gap. The ΔE of as-deposited PPDEA thin films is higher for the applied voltages of 5 and 15 V as compared to those for the iodine-doped ones. The lower value of ∆E of iodine-doped PPDEA thin films indicates formation of charge-transfer-complex.

Polymer chain alignment and transistor properties of nanochannel-templated poly(3-hexylthiophene) nanowires

Nanowires of semiconducting poly(3-hexylthiophene) (P3HT) were produced by a nanochannel-template technique. Polymer chain alignment in P3HT nanowires was investigated as a function of nanochannel widths (W) and polymer chain lengths (L). We found that the ratio between chain length and channel width (L/W) was a key parameter as regards promoting polymer chain alignment. Clear dichroism was observed in polarized ultraviolet-visible (UV-Vis) absorption spectra only at a ratio of approximately L/W = 2, indicating that the L/W ratio must be optimized to achieve uniaxial chain alignment in the nanochannel direction. We speculate that an appropriate L/W ratio is effective in confining the geometries and conformations of polymer chains. This discussion was supported by theoretical simulations based on molecular dynamics. That is, the geometry of the polymer chains, including the distance and tilting angles of the chains in relation to the nanochannel surface, was dominant in determining the longitudinal alignment along the nanochannels. Thus prepared highly aligned polymer nanowire is advantageous for electrical carrier transport and has great potential for improving the device performance of field-effect transistors. In fact, a one-order improvement in carrier mobility was observed in a P3HT nanowire transistor.

An Analytical Solution for Exciton Generation, Reaction, and Diffusion in Nanotube and Nanowire-Based Solar Cells.

Excitonic solar cells based on aligned or unaligned networks of nanotubes or nanowires offer advantages with respect of optical absorption, and control of excition and electrical carrier transport; however, there is a lack of predictive models of the optimal orientation and packing density of such devices to maximize efficiency. Here-in, we develop a concise analytical framework that describes the orientation and density trade-off on exciton collection computed from a deterministic model of a carbon nanotube (CNT) photovoltaic device under steady-state operation that incorporates single- and aggregate-nanotube photophysics published earlier (Energy Environ Sci, 2014, 7, 3769). We show that the maximal film efficiency is determined by a parameter grouping, α, representing the product of the network density and the effective exciton diffusion length, reflecting a cooperativity between the rate of exciton generation and the rate of exciton transport. This allows for a simple, master plot of EQE versus film thickness, parametric in α allowing for optimal design. This analysis extends to any excitonic solar cell with anisotropic transport elements, including polymer, nanowire, quantum dot, and nanocarbon photovoltaics.

Proposed mechanism to represent the suppression of dark current density by four orders with low energy light ion (H−) implantation in quaternary alloy-capped InAs/GaAs quantum dot infrared photodetectors

Here we propose a carrier transport mechanism for low energy H− ions implanted InAs/GaAs quantum dot infrared photodetectors supportive of the experimental results obtained. Dark current density suppression of up to four orders was observed in the implanted quantum dot infrared photodetectors, which further demonstrates that they are effectively operational. We concentrated on determining how defect-related material and structural changes attributed to implantation helped in dark current density reduction for InAs/GaAs quantum dot infrared photodetectors. This is the first study to report the electrical carrier transport mechanism of H− ion-implanted InAs/GaAs quantum dot infrared photodetectors.

Characterization of Highly Concentrated Bi Donors Wire-δ-Doped in Si

We studied the Bi wire-δ-doping process to achieve a high concentration of Bi donors in Si. Our process has two steps: (i) burial of Bi nanowires in Si by molecular beam epitaxy, and (ii) activation of Bi atoms in the δ-doped layer by laser annealing. The peak concentration of Bi atoms in the δ-doped layer is controlled by two parameters: the coverage of surfactant layer, and the growth temperature during the Si cap-layer growth, whose maximum concentration is larger than 1020 cm-3. Photoluminescence and electrical carrier transport measurements reveal that dense Bi atoms are activated upon heating the area at close to the melting point of Si. As a result, our doping process results in Bi donors in the wire-δ-doped layer with concentration of >1018 cm-3. This will be useful for establishing next-generation, quantum information processing platform.

Recent Developments in Bulk Thermoelectric Materials

AbstractGood thermoelectric materials possess low thermal conductivity while maximizing electric carrier transport. This article looks at various classes of materials to understand their behavior and determine methods to modify or “tune” them to optimize their thermoelectric properties. Whether it is the use of “rattlers” in cage structures such as skutterudites, or mixed-lattice atoms such as the complex half-Heusler alloys, the ability to manipulate the thermal conductivity of a material is essential in optimizing its properties for thermoelectric applications.

The modulation of electrical carrier transport in metal-MPCVD diamond due to the microcrystalline inhomogeneous barriers

In the present work, we successfully related the macroscopic electrical transport to the microscopic inhomogeneities of the diamond film. A set of MPCVD diamond Schottky devices shows two distinct Schottky Barrier Heights (SBH), one near 1.1 V (dispersion≈0.15 V) and other near 0.2 V (dispersion≈0.02 V). Two activation energies were found: one near 150 meV (high temperature ionization region) and a very low activation energy near 2 meV (low temperature region, due to hopping effects). The study of the bulk conduction shows some evidence of space charge limited conduction influenced by shallow trap levels, as shown by the differential conductivity analysis. A discussion about a Poole-Frenkel model is included. The calculated macroscopic electrical current is obtained and the correlation with the physical structure is made.

Quantum size aspects of the piezoresistive effect in ultra thin piezoresistors

Proximal probe sensors with an ability to detect extremely small forces (10 −15–10 −18 N) play significant role in scanning probe microscopy applications. The detection of extremely low forces, require producing micromachined cantilevers with as small as possible spring constants, which is considered by the optimization of the sensor design. In the last year many papers describing the fabrication process of producing ultrathin cantilevers (below 100 nm) with integrated piezoresistors for deflection read-out have been published. In the case of such cantilevers the required thickness of piezoresistors is in the range of 50 nm. From a quantum mechanical point of view, an electrical carrier transport confinement in direction perpendicular to the cantilever surface can be expected and in this manner we have to consider the quantum size effect. The goal of the project described in this paper is to calculate and determine the piezoresistive coefficients in p type Si thin (under 50 nm) piezoresistors taking into account the quantum size effect and to compare them with the corresponding coefficients for bulk material. The calculation of the band structure will use the mathematical apparatus of an exact analytical diagonalization six-band k· p model, modified with the envelope function approximation. The behaviour of the thin piezoresistors employed as integrated deflection read-out will be also discussed. Moreover, critical issues in the realization of piezoresistors formed by MOS transistor channel will be presented.

Green OLED's: Electroluminescence and the electrical carrier transport

AbstractOrganic Light Emitting Diodes (OLED) based on metal chelate complexes (Alq3) as the emmiting layer has been prepareded and studied in order to characterise their optical and electrical properties. Electrical measurements have been performed in order to establish the nature of carrier transport. The results point to a trap charge-limited conduction (TCL) with characteristic trap energy near 0.13 eV. In electroluminescence a large green band with a maximum at 2.4 eV was found as a result of three overlapping bands that are correlated with the organic layers. The origin of this luminescence spectrum was analysed.

Molecular Design, Syntheses, and Physical Properties of Nonpolymeric Amorphous Dyes for Electron Transport

Relationships between electrical properties and molecular structures for various nonpolymeric amorphous dyes were investigated. Absorption maximum wavelengths (λobs) for amorphous films were found to be nearly equal to those for solution samples. When the parameters of the used PPP−CI MO method were modified so as to reproduce the λobs values, the calculated HOMO and LUMO energy levels corresponded with the reported ionization potential (Ip) and electron affinity (EA) values. Electric carrier transport properties between dye films and metal electrodes (Au or Al) were found to be correlated with the HOMO and LUMO levels. For strong donor and acceptor dyes, impurity carrier effects were generally observed. For weak donor and acceptor dyes, carrier injection was difficult. Carrier injection phenomena without the influence of impurities were observed for moderate donor and acceptor dye films. Amorphous dyes with cyanovinyl substituents or oxadiazole rings were designed to allow reversible electron transport a...

Mercuric iodide (HgI 2) platelets for x-ray spectroscopy produced by polymer controlled growth

The low temperature red form of mercuric iodide has been grown by a new chemical transport method which introduces organic monomers or polymers during the crystal growth process. Resulting crystals are in the form of platelets which are more directly useful in radiation detector device application. Platelets near one centimeter in width and 200 μm in thickness have been grown in periods of a few days using only 99.9% (unpurified) starting material. Measurements of X-ray and gamma ray energy resolution from detectors fabricated from platelets have yielded a 1.15 keV (FWHM) value for the 59.5 keV Am-241 line and 400 ev (FWHM) for the 5.9 keV Fe-55 line. These are again among the highest resolution values ever measured for HgI 2. Electrical carrier transport property values of HgI 2 so grown equal the best values previously measured from vapor grown material.