High Photoconductivity Research Articles

Electronic structures and optical properties of Cu1-xAgxInTe2 (x = 0, 0.25, 0.5, 0.75 and 1) chalcopyrite compounds

ABC2 chalcopyrite compounds are receiving increasing attention recently, and there are many researches of B-site or C-site doping. The current work mainly redresses the effects of A-site doping. The electronic structures and optical properties of Cu1-xAgxInTe2 (x = 0, 0.25, 0.5, 0.75 and 1) compounds have been investigated by the first-principles approach based on density functional theory (DFT). Cu1-xAgxInTe2 compounds are direct band-gap semiconductors, and the calculated band gaps are respectively 1.128, 1.086, 1.053, 1.029 and 1.01 eV, which coincide well with the experimental results. The Cu1-xAgxInTe2 monocrystals with optical anisotropies have the potential applications in the fields of second harmonic generation and optical parametric oscillator. The polycrystalline Cu1-xAgxInTe2 compounds have high absorption and reflection coefficients. Doping Ag atoms can further increase the photoconductivities of Cu1-xAgxInTe2 compounds. Besides, CuInTe2, Cu0.25Ag0.75InTe2 and AgInTe2 compounds have high absorption capacities and photoconductivities in the visible light region, promising them great potentials to be photoelectric materials.

Electrical and optical properties of epitaxial binary and ternary GeTe-Sb2Te3 alloys

Phase change materials such as pseudobinary GeTe-Sb2Te3 (GST) alloys are an essential part of existing and emerging technologies. Here, we investigate the electrical and optical properties of epitaxial phase change materials: α-GeTe, Ge2Sb2Te5 (GST225), and Sb2Te3. Temperature-dependent Hall measurements reveal a reduction of the hole concentration with increasing temperature in Sb2Te3 that is attributed to lattice expansion, resulting in a non-linear increase of the resistivity that is also observed in GST225. Fourier transform infrared spectroscopy at room temperature demonstrates the presence of electronic states within the energy gap for α-GeTe and GST225. We conclude that these electronic states are due to vacancy clusters inside these two materials. The obtained results shed new light on the fundamental properties of phase change materials such as the high dielectric constant and persistent photoconductivity and have the potential to be included in device simulations.

Self-assembly and photoconductivity of binary porphyrin nanostructures of meso-tetrakis(4-sulfonatophenyl)porphine and Co(III) meso-tetra(4-pyridyl)porphine chloride

The tunable characteristics of the porphyrin molecular tectons have given rise to interest in investigating the self-assembled porphyrin nanoarchitectures for designing new materials. Nanostructures created by the self-assembly of meso-tetrakis(4-sulfonatophenyl)porphine and Co(III) meso-tetra(4-pyridyl)porphine chloride and their photoconductivity are reported here. These nanostructures were characterized by electron microscopy. The ratio of porphyrin tectons in the binary porphyrin nanostructures is about 3:2. The nanostructures demonstrate a high photoconductivity of about 5 × 10−5 S m−1. The dependence of the photoconductivity of the porphyrin nanostructures on the path length and temperature is demonstrated.

Organic Salt Semiconductor with High Photoconductivity and Long Carrier Lifetime

AbstractIntrinsic photogeneration of charge carriers in organic semiconductors is generally attributed to high energy ionization or exciton dissociation by a strong electric field. Here, high bulk photoconductivity is reported in pristine pentamethine cyanine films with photocurrent onset at the band‐edge of the organic semiconductor. Single‐layer cyanine diodes with selective hole and electron contacts show linear dependence of photocurrent with reverse voltage and light intensity. Numerical drift‐diffusion simulations reveal that the linear resistor behavior stems from low and unbalanced carrier mobilities giving rise to negative space charge. Slow bimolecular recombination kinetics of photoinduced charges obtained by time delayed charge extraction measurements show strongly reduced Langevin recombination with long carrier lifetime of the order of a millisecond. Such reduced charge carrier recombination puts forward a materials concept to be exploited in photodiodes and more generally in optoelectronic devices.

High Photoconductivity in Heavily Doped GaAs/AlAs Superlattices with Electric Domains

High Photoconductivity in Heavily Doped GaAs/AlAs Superlattices with Electric Domains

Substrate temperature effects on structural and photoelectric properties of CdS thin films

Cadmium sulfide thin films were deposited on quartz substrates by magnetron sputtering method with varying substrate temperatures. X-ray diffraction patterns of prepared samples showed preferred orientation of (002) with pure hexagonal phase. Atomic force microscopy and scanning electron microscopy images exhibited a surface morphology with uniform and homogeneous grains. X-ray photoelectron spectroscopy (XPS) revealed peaks corresponding to cadmium, sulfur, carbon and oxygen atoms, and the high-resolution XPS surveys for cadmium 3d and sulfur 2p showed an obvious shift to lower binding energy as the substrate temperature raised. Meanwhile, the optical absorption coefficient gradually increased, and the transmittance was approximately 75%. The optical energy gap was as high as 2·40 eV at the substrate temperature of 200°C. Photoconductivity curves presented a rapid response, the lowest conductivity at steady state (only 1·6257 × 10−4 Ω−1 cm−1) and a high solar photoconductivity gain (G p = 296·36) at substrate temperatures of up to 200°C.

Nanostructure and nanomaterial characterization, growth mechanisms, and applications

Abstract Nanostructures are playing significant roles in the development of new functions and the enhancement of the existing functions of industrial devices such as sensors, transistors, diodes, lithium-ion batteries, and photovoltaic cells, due to their piezoelectricity, biocompatibility, and pyroelectrical characteristics. This research focused on the review of the characteristics of different nanostructures and nanomaterials such as ZnO, ZnS, MoS2, GO, TiO2, SnO2, and Fe2O3, their fabrication techniques, growth mechanisms, and applications. The factors affecting the growth mechanisms, the crystallographic natures, growth models of anisotropic nanostructures, and growth of nanocrystals, were also highlighted in this research. The existence of lattice mismatch, differential thermal expansion, and high deposition temperature, have affected uniform deposition of nanoparticles on substrates and caused heteroepitaxy, which has resulted in defective nanostructures. Although heteroepitaxy has negatively affected the characteristics and potential applications of nanostructures, it has also opened new research frontiers for potential new applications of nanostructures. The use of nanostructures for gas sensing is attributed to the high specific area, change of resistance on exposure to gases, and high photoconduction abilities, while the photon-carrier collection abilities and anti-reflectance qualities are vital for solar photovoltaic cells. Nanostructures have also been used as coating pigments to prevent corrosion of facilities, reduce urban heat islands and energy consumptions, due to the near infrared (NIR) reflective characteristics.

Efficient Solar Cells Based on Light‐Harvesting Antimony Sulfoiodide

AbstractAlthough antimony sulfoiodide (SbSI) exhibits very interesting properties including high photoconductivity, ferroelectricity, and piezoelectricity, it is not applied to solar cells. Meanwhile, SbSI is predominantly prepared as a powder using a high‐temperature, high‐pressure system. Herein, the fabrication of solar cells utilizing SbSI as light harvesters is reported for the first time to the best of knowledge. SbSI is prepared by solution processing, followed by annealing under mild temperature conditions by a reaction between antimony trisulfide, which is deposited by chemical bath deposition on a mesoporous TiO2 electrode and antimony triiodide, under air at a low temperature (90 °C) without any external pressure. The solar cells fabricated using SbSI exhibit a power conversion efficiency of 3.05% under standard illumination conditions of 100 mW cm−2.

Heteroleptic neutral Ru(II) complexes based photodiodes

The two complexes Ru(II) containing 2,6-bis(benzimidazol-2-yl)pyridine and 2-pyridine and 2-quinoline carboxylates were synthesized to fabricate organic photodiodes. The electrical properties of Au/Ru(II) complex (I)/n−Si/Al and Au/Ru(II)complex (II)/n−Si/Al diodes were investigated by current-voltage and capacitance-voltage measurements. The fabricated devices give a high rectification behavior with rectification ratio of 2.4 ×104 −2.1 ×103 at ±4 V. The diodes exhibited a high photoconductivity based on trap levels within band gap. The series resistance and barrier height were calculated from (C−V) measurements and compared to other of (I−V). The obtained results indicate that the prepared photodiodes can be used as photosensor for optoelectronic applications.

TiO2 mesocrystals composited with gold nanorods for highly efficient visible-NIR-photocatalytic hydrogen production

TiO2 mesocrystals (TMC) have efficient charge transport properties and long-lived charges which cause high photoconductivity and photocatalytic activity. However, TMC have no absorption in the region of visible and near-Infrared (NIR) light. The optical resonance of Au nanorods (NRs) depending mainly on their length and width (aspect ratio) can be used to design panchromatic absorbers, covering most of the useful solar spectrum. Therefore, in this article, Au NRs and TMC composites were prepared by the ligand exchange method to show highly efficient H2 production (924µmolh−1g−1) under visible-NIR light irradiation. The efficient H2 production is explained by surface plasmon resonance (SPR) of Au NRs, electron injection to TMC, efficient charge transport in TMC due to the superstructure of TMC and water reduction on TMC. Single-particle confocal fluorescence microscopy and time-resolved diffuse reflectance measurements confirmed the efficient hot electron injection and charge separation from Au NRs with strong SPR to the superstructure of TMC.

Enhanced photoelectric gas sensing performance of SnO2 flower-like nanorods modified with polyoxometalate for detection of volatile organic compound at room temperature

SnO2 has become most popular sensor material because of its excellent optical and electrical properties, but the existence of fast electron-hole recombination in SnO2 material is a critical limitation on developing high-performance gas sensors based on the photoconductive change. Herein, we investigate on polyoxometalate (C4H10ON)23[HN(CH2CH2OH)3]10H2[FeIII(CN)6(α2-P2W17O61CoII)4]·27H2O (abbr. as HPT) doping on SnO2 nanorods for improving gas sensing of formaldehyde and methylbenzene at room temperature (25°C). The relevant photoconductivity and gas sensing performances demonstrated that the SnO2/HPT composite film had a higher photoconductivity than the pristine SnO2 film. This was attributed to the occurrence of photoinduced electron transfer from SnO2 to HPT, so that the electron-hole recombination in SnO2 could effectively be retarded. Furthermore, the composite film of SnO2/HPT exhibited obvious improvements in photoelectrical gas sensing of formaldehyde and methylbenzene at room temperature. This study represents a new insight into improving the sensing performance of SnO2-based gas sensors by incorporating polyoxometalate.

ZnO:Mo:In nanofilms on SiO2 substrate under investigation framework of the second optical transition

ZnO and ZnO:Mo:In nanofilms were deposited on SiO2 substrate at 460 °C by the spray pyrolysis method with the molar ratio (Mo/Zn) set at 1% and (In/Zn) dosed at 1%, 2%, 3% and 10%. The optical, dielectric and photonic characteristics of these samples were analyzed from the optical spectra of transmission and reflection, which revealed the presence of two absorption edges. The first one was related to the ZnO:Mo:In typical transition and the second edge originated from the ZnO:Mo:In/SiO2 interface transition by the probable formation of an ultrafine layer identified as SiOx and/or ZnO(1−x)SiO2(x). The optical gap and Urbach energies of ZnO:Mo:In nanofilms varied almost uniformly and in a complementary manner depending on the co-doping of ∼3.28–3.24 eV and ∼82–136 meV. These energies associated with the interface varied randomly from 3.93 to 4.18 eV and ∼263 to 408 meV, and showed strong dependencies with the structural, crystalline and vibrational properties previously studied. They also displayed possible correlations with electron scattering time and the dc photoconductivity which reaches high value for film prepared using In = 2%. AFM study showed variable morphologies of the surfaces that are responsive to codoping elements, therefore at the interface, wherein the film growth began. All these factors influenced the results described above. The study also showed good agreement between rms roughness and TC texture coefficient of the studied films, of high transparency ∼89–92%. The films prepared with In = 2% revealed a high photoconductivity and could be used in photocatalytic and photonic applications.

Dye characteristics of Zingiber officinale var rubrum, Cinnamomum zaylanicum, Curcuma longa L., Oryza sativa L. Indica in dye sensitized solar cell (DSSC)

The aims of the research to were know performance of DSSC using the dye of Zingiber, Cinnamomum, Curcuma, and Oryza as a photosensitizer with a variation of dye deposition area with spin coating techniques. The structure of the samples as a sandwich consisting of the working electrode (TiO2), dye, electrodes of platinum (Pt) and the electrolyte sandwiched between two electrodes. Test absorbance dye using UV-Visible Spectrophotometer Lambda 25, using a two-point conductivity test probes El Kahfi 100 and characterization test IV using a Keithley 2602A. For Zingiber results showed that absorbance at 243 nm and 279 nm, photoconductivity of 0.29 Ω-1m-1 and the efficiency is 0.015% on 0.5 cm2. Cinnamomum results showed that absorbance at 253 nm and 403 nm, photoconductivity of 0.11 Ω-1m-1 and the efficiency is 0.002% on 3 cm2. Curcuma results showed that absorbance at 243 nm and 422 nm, photoconductivity of 0.177 Ω-1m-1 and the efficiency is 0.072% on 3 cm2. Oryza results showed that absorbance at 240 nm and 423 nm, photoconductivity of 0.21 Ω-1m-1 and the efficiency is 0.04% on 2.25 cm2. Best absorbance value was obtained from Oryza dye; the highest photoconductivity was obtained from Zingiber dye, and the highest efficiency was obtained from Curcuma dye.

Enhanced photoactivity and conductivity in transparent TiO2nanocrystals/graphene hybrid anodes

An optically transparent and UV-light active anode, characterized by high (photo)conductivity, charge mobility and exciton lifetime, based on CVD graphene, decorated with colloidal TiO2nanocrystals, has been fabricated, by a solution-based procedure.

Functional Sulfur-Doped Buckybowls and Their Concave-Convex Supramolecular Assembly with Fullerenes.

Buckybowls are fascinating components of supramolecular assemblies owing to their unique bowl-shaped π-surfaces. Herein we present a protocol for the functionalization of a sulfur-doped buckybowl, trithiasumanene, via a brominated intermediate, from which thiolated trithiasumanenes were derived. The curved surface and electron-donating properties of thiolated trithiasumanenes promote their ready assembly with fullerenes to form concave-convex complexes. The supramolecular assembly behavior in solution was investigated by NMR analysis. The structures of supramolecular complexes were unambiguously characterized by crystallography. The crystals of the concave-convex complexes showed high thermal stability and photoconductivity.

Functional Sulfur‐Doped Buckybowls and Their Concave–Convex Supramolecular Assembly with Fullerenes

AbstractBuckybowls are fascinating components of supramolecular assemblies owing to their unique bowl‐shaped π‐surfaces. Herein we present a protocol for the functionalization of a sulfur‐doped buckybowl, trithiasumanene, via a brominated intermediate, from which thiolated trithiasumanenes were derived. The curved surface and electron‐donating properties of thiolated trithiasumanenes promote their ready assembly with fullerenes to form concave–convex complexes. The supramolecular assembly behavior in solution was investigated by NMR analysis. The structures of supramolecular complexes were unambiguously characterized by crystallography. The crystals of the concave–convex complexes showed high thermal stability and photoconductivity.

Template-Free Electrochemical Synthesis of Selenium Nanowires

During past years, one-dimensional nanostructures such as nanotubes and nanowires have drown much attention due to the possibility of their application in nanodevices. This is due to their size-dependent physical properties. Selenium is known to be an important elemental semiconductor which has been widely studied because of the exhibition of so many appealing properties such as high photoconductivity and low photomelting temperature, high piezoelectric, thermoelectricity, and non-linear optical responses. There has been extensive research on Selenium nanowires and nanorods among all Se nanostructures. Se nanowires can be fabricated by using solution-phase method, chemical vapor deposition method, and electrodeposition. The electrodeposition technique is more promising due its simplicity, cost-effectiveness, and low growth temperature. In the present work, we are looking forward to fabricating one-dimensional trigonal Selenium nanowires using electrodeposition. The morphology is controlled as a function of applied potential and pH in the electrolytes. The temperature-dependent annealing will also be performed. The morphology and crystallinity of the Se nanostructures are characterized by Raman spectra, TEM, SEM, and XRD. The electrodeposition of trigonal Selenium nanostructures is demonstrated based on an analysis of linear sweep voltammetry and pH-Eh (pourbaix) diagram.

Defective TiO2 with high photoconductive gain for efficient and stable planar heterojunction perovskite solar cells.

Formation of planar heterojunction perovskite solar cells exhibiting both high efficiency and stability under continuous operation remains a challenge. Here, we show this can be achieved by using a defective TiO2 thin film as the electron transport layer. TiO2 layers with native defects are deposited by electron beam evaporation in an oxygen-deficient environment. Deep-level hole traps are introduced in the TiO2 layers and contribute to a high photoconductive gain and reduced photocatalytic activity. The high photoconductivity of the TiO2 electron transport layer leads to improved efficiency for the fabricated planar devices. A maximum power conversion efficiency of 19.0% and an average PCE of 17.5% are achieved. In addition, the reduced photocatalytic activity of the TiO2 layer leads to enhanced long-term stability for the planar devices. Under continuous operation near the maximum power point, an efficiency of over 15.4% is demonstrated for 100 h.

Ultrahigh photoconductivity of bandgap-graded CdSxSe1-x nanowires probed by terahertz spectroscopy.

Superiorly high photoconductivity is desirable in optoelectronic materials and devices for information transmission and processing. Achieving high photoconductivity via bandgap engineering in a bandgap-graded semiconductor nanowire has been proposed as a potential strategy. In this work, we report the ultrahigh photoconductivity of bandgap-graded CdSxSe1−x nanowires and its detailed analysis by means of ultrafast optical-pump terahertz-probe (OPTP) spectroscopy. The recombination rates and carrier mobility are quantitatively obtained via investigation of the transient carrier dynamics in the nanowires. By analysis of the terahertz (THz) spectra, we obtain an insight into the bandgap gradient and band alignment to carrier transport along the nanowires. The demonstration of the ultrahigh photoconductivity makes bandgap-graded CdSxSe1−x nanowires a promising candidate as building blocks for nanoscale electronic and photonic devices.

Hydrogenated Amorphous Silicon Germanium Active Layer for Top Cell of a Multi Junction Cell Structure.

Intrinsic hydrogenated amorphous silicon-germanium (a-SiGe:H) alloy is generally used in the bottom cell because of its low band gap. The a-SiGe:H has a higher photo conductivity in comparison to the a-Si:H; thus, it is expected that the a-SiGe:H can show better short circuit current density than that of the a-Si:H based solar cell. Therefore, we optimized a-SiGe:H active layer that can be a suitable choice for the front cell of a multi junction.solar cell. Furthermore, we carried out a comparative study of the solar cells that have a-SiGe:H and a-Si:H as respective active layers. The a-SiGe:H based solar cells show higher short circuit current density, while the a-Si:H based cells show higheropen circuit voltage. The current-voltage characteristics of these cells are as follows: (a) V(oc) = 770 mV, J(sc) = 15.0 mA/cm2, FF = 64.5%, and η = 7.47% for a-SiGe:H based cell; and (b) V(oc) = 826 mV, J(sc) = 13.63 mA/cm2, FF = 72.0%, and η = 8.1% for a-Si:H based cell.