Values Of Charge Carrier Mobility 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.

Entropy engineering enabled atomically dispersed Cu doping leading to an exceptionally high thermoelectric figure of merit in n-type lead chalcogenides

Entropy engineering fully dissolved extra Cu atoms into the interstitial lattice sites of lead chalcogenides, yielding high charge carrier mobility and ZT values in a wide temperature range.

Optical Absorption, Photocarrier Recombination Dynamics and Terahertz Dielectric Properties of Electron-Irradiated GaSe Crystals

Optical absorption spectra of 9 MeV electron-irradiated GaSe crystals were studied. Two absorption bands with the low-photon-energy threshold at 1.35 and 1.73 eV (T = 300 K) appeared in the transparency region of GaSe after the high-energy-electron irradiation. The observed absorption bands were attributed to the defect states induced by Ga vacancies in two charge states, having the energy positions at 0.23 and 0.61 eV above the valence band maximum at T = 300 K. The optical pump-terahertz probe technique (OPTP) was employed to study the dark and photoexcited terahertz conductivity and charge carrier recombination dynamics at two-photon excitation of as-grown and 9 MeV electron-irradiated GaSe crystals. The measured values of the differential terahertz transmission at a specified photoexcitation condition were used to extract the terahertz charge carrier mobilities. The determined terahertz charge carrier mobility values were ~46 cm2/V·s and ~14 cm2/V·s for as-grown and heavily electron-irradiated GaSe crystals, respectively. These are quite close to the values determined from the Lorentz–Drude–Smith fitting of the measured dielectric constant spectra. The photo-injection-level-dependent charge carrier lifetimes were determined from the measured OPTP data, bearing in mind the model injection-level dependencies of the recombination rates governed by interband and trap-assisted Auger recombination, bulk and surface Shockley–Read–Hall (SRH) recombination and interband radiative transitions in the limit of a high injection level. It was found that GaSe possesses a long charge carrier lifetime (a~1.9 × 10−6 ps−1, b~2.7 × 10−21 cm3ps−1 and c~1.3 × 10−37 cm6ps−1), i.e., τ~0.53 μs in the limit of a relatively low injection, when the contribution from SRH recombination is dominant. The electron irradiation of as-grown GaSe crystals reduced the charge carrier lifetime at a high injection level due to Auger recombination through radiation-induced defects. It was found that the terahertz spectra of the dielectric constants of as-grown and electron-irradiated GaSe crystals can be fitted with acceptable accuracy using the Lorentz model with the Drude–Smith term accounting for the free-carrier conductivity.

Electrical Relaxation and Transport Properties of ZnGeP2 and 4H-SiC Crystals Measured with Terahertz Spectroscopy

Terahertz photoconductivity and charge carrier recombination dynamics at two-photon (ZnGeP2) and three-photon (4H-SiC) excitation were studied. Thermally annealed, high-energy electron-irradiated and Sc-doped ZnGeP2 crystals were tested. The terahertz charge carrier mobilities were extracted from both the differential terahertz transmission at a specified photoexcitation condition and the Drude–Smith fitting of the photoconductivity spectra. The determined terahertz charge carrier mobility values are ~453 cm2/V·s for 4H-SiC and ~37 cm2/V·s for ZnGeP2 crystals. The charge carrier lifetimes and the contributions from various recombination mechanisms were determined at different injection levels using the model, which takes into account the influence of bulk and surface Shockley–Read–Hall (SRH) recombination, interband radiative transitions and interband and trap-assisted Auger recombination. It was found that ZnGeP2 possesses short charge carrier lifetimes (a~0.01 ps−1, b~6 × 10−19 cm3·ps−1 and c~7 × 10−40 cm6·ps−1) compared with 4H-SiC (a~0.001 ps−1, b~3 × 10−18 cm3·ps−1 and c~2 × 10−36 cm6·ps−1), i.e., τ~100 ps and τ~1 ns at the limit of relatively low injection, when the contribution from Auger and interband radiative recombination is small. The thermal annealing of as-grown ZnGeP2 crystals and the electron irradiation reduced the charge carrier lifetime, while their doping with 0.01 mass % of Sc increased the charger carrier lifetime and reduced mobility. It was found that the dark terahertz complex conductivity of the measured crystals is not fitted by the Drude–Smith model with reasonable parameters, while their terahertz photoconductivity can be fitted with acceptable accuracy.

Transparent and highly conductive La-doped strontium stannate thin film growth by PI-MOCVD method on LaAlO3 and MgO substrates of (100), (110), (111) orientations

Wide band gap (4.6 eV) lanthanum doped SrSnO3 semiconductors of high electron mobility have potential applications in transparent oxide semiconductor technologies. However, there is a lack of data on the electrical properties of La:SrSnO3 both in single crystals and in thin films with an orientation other than (001). We show that after applying a modified metalorganic chemical vapor deposition method it is possible to deposit relaxed thick (001), (110) and (111) oriented La:SrSnO3 films on LaAlO3 and MgO substrates. Thin films on LaAlO3 substrates exhibit comparatively high charge carrier mobility values: µ100=71 cm2V−1s−1, µ110=72 cm2V−1s−1 and µ111=67 cm2V−1s−1. In this article, using the results of X-ray diffraction and crystallite orientation distribution modeling, as well as scanning and transmission electron microscopy data, the link between the obtained charge carrier mobility (µ100 ≈ µ110 > µ111) and film's microstructure and morphology is discussed.

A model for prognosis of influence of radiation dose on value of charge carrier mobility: an analytical approach for analysis of the introduced model

In this paper, we analyzed the dependence of charge carriers mobility on value of radiation dose during ion implantation. Based on the considered model, we determine conditions to decrease radiation damage in the irradiated materials. Also we introduce an analytical approach to analyze mass transfer in the irradiated materials. The approach gives a possibility to take into account nonlinearity of the considered process, as well as changes of parameters of the considered process in space and time at one time.

On Prognosis of Influence of Radiation Dose on Value of Charge Carrier Mobility

In this paper, we introduce a model to analyze the manufacturing of an implanted-junction rectifier. The model gives a possibility to analyze dependence of charge carriers mobility on the value of dose of implanted ions. Also, we introduce an analytical approach to analyze mass transfer. The approach gives a possibility to make the analysis in a more common situation, as was recently done in the literature. Analysis of the introduced model shows an increae in the spread of distribution of dopant and decrease of mismatch-induced stresses in multilayer structures with increase of dose of implanted ions.

Impact of charge carrier transport properties on conductivity-temperature dependence of gellan gum-LiCF3SO3 biopolymer electrolyte

Charge carrier density, mobility and diffusivity are three important transport properties in determining the ionic conductivity as well as the performance of solid polymer electrolyte. In this work, biopolymer electrolytes samples were prepared using the solution casting method by complexing gellan gum with different concentrations of lithium trifluoromethanesulfonate (3–15 wt.%). The values of charge carrier concentration, mobility, and diffusivity for electrolyte samples were estimated by fitting the Nyquist plot with an equation developed based on electrical impedance spectroscopy. At room temperature, the optimum electrolyte conductivity is 1.29×10−8 Scm−1 at 6 wt.% salt concentration. This result was supported by the highest percentage of free ions, 31.45%, observed in the FTIR method. As the temperature increases, the ionic conductivity increases to the optimum value before dropping. The highest conductivity of each sample was obtained at different temperatures (80°C–90°C) using the impedance method, whereas the percentage area of free ions was highest at 80°C for all samples with FTIR analysis. Overall, the ionic conductivity of this system has been dominated by the carrier charge density. Results suggest that, under these experimental conditions, electrical impedance spectroscopy is suitable for evaluating the charge transport properties at low temperatures.

Double perovskite Cs2AgBiBr6 radiation sensor: synthesis and characterization of single crystals

Single crystals of lead-free halide double perovskite Cs2AgBiBr6 sensor material manifest a remarkable potential for application in radiation detection and imaging. In this study, the purity and crystallinity of solution-grown Cs2AgBiBr6 single crystals with cubic Fmoverline{3}m symmetry have been corroborated by powder XRD measurements, while the single crystal XRD patterns reveal the dominant {111} lattice planes parallel to the sample surfaces. A wider range of lower resistivity values (106–109 Ωcm) was obtained from the I-V measurements compared to the 1.55 × 109–6.65 × 1010 Ωcm values from the van der Pauw method, which is typically higher for the Ag than for the carbon paint electrodes. Charge-carrier mobility values estimated from the SCLC method for the carbon paint-Cs2AgBiBr6 (1.90–4.82 cm2V−1 s−1) and the Ag-Cs2AgBiBr6 (0.58–4.54 cm2V−1 s−1) including the density of trap states (109–1010 cm−3) are comparable. Similar values of 1.89 cm2V−1 s−1 and 2.36 cm2V−1 s−1 are derived from the Hall effect measurements for a sample with carbon and Ag electrodes, respectively. The key electrical parameters including the X-ray photoresponse measurements indicate that the Cs2AgBiBr6 samples synthesized in this study satisfy requirements for radiation sensors.Graphical abstract

Synergistic degradation of organic pollutants by poly (3,4-ethylenedioxythiophene) based photo-electrocatalysis

Poly (3,4-ethylenedioxythiophene) (PEDOT) had been explored as photosensitizer and hole transport agent. However, coating PEDOT on metal electrodes had issues with poor adhesion and delamination. In this work, the composite electrode with improved photo-electrocatalytic performance was constructed by potentiostatic polymerization of PEDOT on graphite plate and subsequent loading of ZnIn2S4. Solid micro-nanowires were observed in pure ZnIn2S4 electrode, which changed to polygon hollow tubular structure when loading ZnIn2S4 on PEDOT surface. From the Hall effect results, the resistance of composite electrode was reduced and the carriers density and mobility were increased. The charge carrier mobility value was 173.15 cm−2·V−1·s−1, which was almost two and four times higher than PEDOT (85.90 cm−2·V−1·s−1) and ZnIn2S4 (42.90 cm−2·V−1·s−1), respectively. The optimum EDOT concentration and polymerization time of PEDOT were 0.01 M and 20 min, respectively. The optimum scanning cycles for cyclic voltammetry deposition of ZIS and the ratio of ZnCl2, InCl·4H2O and Na2S2O3·5H2O were 400 cycles and 2:4:8, respectively. The radical capture experiment showed that singlet oxygen (1O2) and superoxide radical (O2−) were produced by PEDOT anode, while 1O2, O2− and hydroxyl radical (OH) were produced by the composite cathode. Through these reactive species, the removal of tetracycline and methylene blue reached 91% and 99% after 180 min reaction, respectively, under external voltage of 0.9 V.

Фотофизические свойства тонких пленок перилена, модифицированного функциональными группами диангидрида и диимида тетракарбоновой кислоты

The morphology of organic semiconductor films of perylenetetracarboxylic acid dianhydride (PTCDA) and perylenetetracarboxylic acid dibenzyl-diimide (N, N`-DBPTCDI) formed by thermal vacuum deposition was studied by atomic force microscopy. It was shown that annealing of films at 420 K leads to rearrangement of their structure and crystallization. The optical absorption spectra of the films under study were used to estimate the optical band gap. The temperature dependence of the dark conductivity of PTCDA and N, N-DBPTCDI films before and after annealing (Т = 420 K) was established. The values of the activation energy of charge carrier traps are determined. The computer simulation of the density of localized states in the band gap of the films studied was carried out using the photoconductivity spectra in the constant photocurrent mode. Model photovoltaic cells based on PTCDA / СuPc and N, N-DBPTCDI / СuPc structures were formed. The kinetics of decay of the interfacial photo-voltage of the cells prepared was measured using pulsed light as an excitation source. On the basis of the performed measurements, the charge carrier mobility values in the investigated semiconductor materials were estimated.

Design Rules to Maximize Charge-Carrier Mobility along Conjugated Polymer Chains.

The emergence of polymeric materials displaying high charge-carrier mobility values despite poor interchain structural order has spawned a renewal of interest in the identification of structure-property relationships pertaining to the transport of charges along conjugated polymer chains and the subsequent design of optimized architectures. Here, we present the results of intrachain charge transport simulations obtained by applying a robust surface hopping algorithm to a phenomenological Hamiltonian parametrized against first-principles simulations. Conformational effects are shown to provide a clear signature in the temperature-dependent charge-carrier mobility that complies with recent experimental observations. We further contrast against molecular crystals the evolution with electronic bandwidth and electron-phonon interactions of the room-temperature mobility in polymers, showing that intrachain charge-carrier mobility values in excess of 100 cm2/(V s) can be achieved through a proper chemical engineering of the backbones.

Organic heterojunctions of phthalocyanine-reduced graphene oxide above percolation threshold for photovoltaic application

In this article, non-fullerene, cost effective, and highly soluble zinc tetra-tert-butyl phthalocyanine-reduced graphene oxide (ZnTTBPc-RGO) heterojunction have been used as an active layer in organic photovoltaic devices. The RGO content in the active material is varied from 0.25–0.5 volume fractions which are above the percolation threshold of 0.167 volume fraction of RGO. Temperature dependent current density–voltage characteristics show a transition from Ohmic conduction to space charge limited current (SCLC) conduction at higher applied bias voltages (≥1 V). This enables us to extract charge carrier mobility values of the heterojunction at different temperatures using a trap-free SCLC model. A donor–acceptor solution processable photovoltaic device with 0.33 vol.% RGO content of active layer show the highest power conversion efficiency of 1.02%, highest recombination resistance of 48.65 kΩ, and maximum carrier mobility of 4.32 × 10−4 cm2V−1s−1 among the three devices studied. 80 h exposure to ambient conditions see a ∼40% decay of power conversion efficiency. Quantitative analysis on the density of trap states indicates that the best power conversion efficiency and the highest charge carrier mobility correlate well with a minimum of the trap density and a maximum of recombination resistance for these devices.

Electrical Transport Properties of Nb and Ga Double Substituted Fe2VAl Heusler Compounds

In this work the results of studying the electrical transport properties of Fe2V1 –xNbxAl1 –yGay (0.1 ≤ x ≤ 0.2 and 0.1 ≤ y ≤ 0.2) are presented. The specimens were fabricated using conventional arc-melting method followed by ball milling and spark plasma sintering. It was shown that dual-site substitution approach may lead to a more noticeable changes in the Seebeck coefficient and the electrical resistivity comparing to single-site substitution. Since such substitution can be assumed as isovalent one, the evolution of the electrical transport properties was mainly attributed to the changes in the band gap and charge carrier mobility values. To testify applicability of computational methods on these samples we have used well-known density functional theory and Boltzmann transport equation solving on one of the samples.

Phonon characteristics of Si‐doped InAs grown by gas‐source molecular beam epitaxy

AbstractUsing Raman scattering spectroscopy with 514‐ and 633‐nm light sources, we have studied the phonon characteristics of Si‐doped InAs films grown on (100) n‐type InAs by gas‐source molecular beam epitaxy having charge carrier concentration (n) between 2.26 × 1018 and 1.68 × 1020 cm−3. The unscreened longitudinal optical (LO) phonon is observed near ~238 cm−1 along with two plasmon‐LO‐phonon (PLP) coupled L± modes. With increasing n, the L− mode is downshifted from the LO phonon towards the transverse optical mode frequency. This abnormal behavior is ascribed to the large scattering vector and heavy Landau damping. The L+ mode close to the plasma frequency ωP is also detected in samples with n > 1019 cm−3. The observed unscreened LO mode in the forbidden configuration is attributed to the resonance enhanced scattering induced by surface space charge. Reliable values of charge carrier density and mobility are estimated from the simulated shifts of PLP modes in the low Si‐doped InAs films. At higher doping level, a full‐line shape analysis is desired for assessing accurate values of the transport parameters. In Si‐doped InAs, we appraised the existing experimental data of localized vibrational modes (LVMs) from Raman and Fourier transform infrared spectroscopy by exploiting a sophisticated Green's function theory and incorporating lattice relaxation effects around SiIn and SiAs defects for constructing accurate perturbation models. The simulated results of LVMs for several isolated (Td) defects, nearest neighbor pair (C3v), and next‐nearest neighbor complex centers (Cs) are compared, contrasted, and discussed with the experimental data.

Mask-free patterning and selective CVD-growth of 2D-TMDCs semiconductors

This work reports on a novel mask-free approach that enables controlled selective growth of molybdenum disulfide (MoS2) and tungsten disulfide (WS2) crystalline islands on Si/SiO2 substrates. In particular, the direct-write patterning technique and chemical vapor deposition method are employed to produce arrays of 2D-TMDCs nanostructures at pre-defined locations on the substrates. It is shown that by adjusting the patterning parameters, composition and concentrations of ink-precursors, and the growth conditions, patterns of MoS2 and WS2 nanostructures with controlled geometry can be produced. The prepared 2D-TMDCs materials were analyzed by atomic force microscopy, Raman spectroscopy, transmission electron microscopy, and x-ray photoelectron spectroscopy, all of which indicated to high-quality double-layer MoS2 and WS2 nanostructures. The back-gated field effect transistors were fabricated, and their charge carrier mobility values of 11 cm2 V−1 s−1 for MoS2 and 4 cm2 V−1 s−1 for WS2 were extracted from the device measurements.

Principles of Structural Design of Conjugated Polymers Showing Excellent Charge Transport toward Thermoelectrics and Bioelectronics Applications.

Conjugated polymers, especially their second generation with a donor-acceptor alternating structure, have promising properties. These are suitable for two emerging fields, thermoelectrics and bioelectronics, if appropriate structural designs are implemented. This review aims to give a perspective for the potential and challenges of novel conjugated polymers in such applications. In particular, the aspects of synthetic design and the consequences of modifications of the chemical structure on the charge transport in selected second-generation conjugated polymers are reviewed. By understanding the effects of structural motifs on the overall material properties, polymers can be specifically tailored for the respective application. The basics of charge transport measurements are briefly summarized, as the charge transport plays an important role for thermoelectrics as well as for bioelectronics. In particular, the correlation between the reported charge carrier mobility values and the structural design of the polymers is reviewed. Examples of the application of second-generation conducting polymers in thermoelectrics and bioelectronics are shown to demonstrate the current state of research. Finally, the prospect of a purposeful design of new materials for these two emerging fields is discussed.

64‐4: Manufacturing and Encapsulation Process of Bottom Gate Bottom Contact Thin‐Film Transistors with a Printed Oxide Semiconductor

We present bottom gate bottom contact staggered oxide semiconductor TFTs, manufactured by using an ink‐jet printed metal oxide semi‐conductor material from the company Evonik. The printed TFTs with optimized process and adjusted channel geometry present high charge carrier mobility values between 10 and 15 cm2/Vs and on/off current‐ratios of more than 106 . The maximum temperature used is 300 °C, which makes the process compatible with the display manufacturing. To achieve a more stable electric behavior and better threshold voltage homogeneity, mainly in the case of positive gate bias stress, we used a solution processed encapsulation to shield the device from the atmospheric effects. The encapsulated TFTs show a considerable stability improvement and present hence an attractive technology alternative for active matrix processes.

Influence of Mismatch-Induced Stress in a Heterostructure on Value of Charge Carrier Mobility

Influence of Mismatch-Induced Stress in a Heterostructure on Value of Charge Carrier Mobility

Charge-Carrier Mobilities in Metal Halide Perovskites: Fundamental Mechanisms and Limits

Perovskite photovoltaic cells have seen a remarkable rise in power conversion efficiencies over a period of only a few years. Much of this performance is underpinned by the favorable charge-carrier mobilities in metal halide perovskites (MHPs), which are remarkably high for materials with such facile and versatile processing routes. This Perspective outlines the mechanisms that set a fundamental upper limit to charge-carrier mobility values in MHPs and reveals how they may be tuned through changes in stoichiometry. In addition, extrinsic effects such as grain size, energetic disorder, and self-doping are discussed for specific MHPs in the context of remedies designed to avoid them.