Light Current-voltage Characteristics Research Articles

InAs thermophotovoltaic cells with high quantum efficiency for waste heat recovery applications below 1000 °C

InAs thermophotovoltaic (TPV) cells with external quantum efficiency at the peak wavelengths reaching 71% at low temperature and 55% at room temperature are reported, which are the highest values to date for InAs. The TPV exhibited 10% power conversion efficiency at 100K cell temperature. The dark and light current-voltage characteristics were measured at different cell temperatures (100–340K) in response to heat sources in the range 500–800°C. The resulting dependences of the output voltage and current as well as the spectral response of the InAs TPV have been extensively characterized for waste heat recovery applications. The performance of these cells is strongly determined by the dark current which increases rapidly with increasing cell temperature originating from bandgap narrowing, which resulted in a reduction of open circuit voltage and output power.

Characterization of the nanosandwiched Ga2S3/In/Ga2S3 interfaces as microwave filters and thermally controlled electric switches

In this work, an indium layer of 50nm thicknesses is sandwiched between two 500nm thick Ga2S3 layers. The effect of indium nansandwiching on the composition, structure, morphology, light absorbability, capacitance and reactance spectra, and temperature dependent electrical conductivity of the Ga2S3 films are investigated by means of X-ray diffraction, scanning electron microscopy, energy dispersion X-ray spectroscopy, Raman spectroscopy, visible light spectrophotometry, impedance spectroscopy and current voltage characteristics. While the nansandwiched films are observed to exhibit an amorphous nature of structure with indium content of Owing to the nucleation mechanisms that take place during the film growth, the accumulation of some unit cells in groups to form grains should be a significant reason for the existence of many different sizes of grains in the nanosandwiched films (Alharbi and Qasrawi, 2016). O, the Raman spectra displayed three vibrational modes at 127.7, 145.0 and 274.3cm−1. It was also observed that the indium insertion in the structure of the Ga2S3 shrinks the energy band gap by 0.18eV. The nanosandwiched films are observed to exhibit a semiconductor −metal (SM) transition at 310K. The SM transition is associated with thermal hysteresis that exhibited a maximum value of 16% at 352K. This behavior of the nanosandwiched films nominate it for use as thermally controlled electric switches. In addition, the impedance spectral analysis in the range of 10–1800MHz has shown a capacitance tunability of more than 70%. The measurements of the wave trapping property displayed a bandpass/reject filter characteristics above 1.0GHz which allow using the Ga2S3/In/Ga2S3 thin films as microwave resonator.

Identification and Analysis of Hazardous Materials Using Optical Spectroscopy

This investigation is aimed towards using optical spectroscopy for remote identification and quantitative analysis of hazardous substances for safety and security applications. We introduce a new model employing portable photosensor devices that are based on the double-barrier and vertically placed silicon structure, for such applications. The different absorption depths of individual waves allow us to carry out their spectral selection using an algorithm developed for this specific objective. We tested the proposed model on experimental Ag-p-Si-n-Si structures. The algorithm is developed for the spectral analysis without the preliminary calibration. The low dark currents (several dozens of pA) permit us to carry out the spectral analysis of the integral flux of the electromagnetic radiation of low intensity. The quantitative data from light current-voltage characteristics allow us to obtain an intensity distribution spectrum characteristic of the material by using red LED and the green laser. The results of this investigation divulge new possibilities for the creation of a new type of the portable semiconductor spectrophotometer and due to its stand-off detection capability, offer potential pathways to evaluate hazardous substances.

Asymmetric band offsets in silicon heterojunction solar cells: Impact on device performance

Amorphous/crystalline silicon interfaces feature considerably larger valence than conduction band offsets. In this article, we analyze the impact of such band offset asymmetry on the performance of silicon heterojunction solar cells. To this end, we use silicon suboxides as passivation layers—inserted between substrate and (front or rear) contacts—since such layers enable intentionally exacerbated band-offset asymmetry. Investigating all topologically possible passivation layer permutations and focussing on light and dark current-voltage characteristics, we confirm that to avoid fill factor losses, wider-bandgap silicon oxide films (of at least several nanometer thin) should be avoided in hole-collecting contacts. As a consequence, device implementation of such films as window layers—without degraded carrier collection—demands electron collection at the front and hole collection at the rear. Furthermore, at elevated operating temperatures, once possible carrier transport barriers are overcome by thermionic (field) emission, the device performance is mainly dictated by the passivation of its surfaces. In this context, compared to the standard amorphous silicon layers, the wide-bandgap oxide layers applied here passivate remarkably better at these temperatures, which may represent an additional benefit under practical operation conditions.

Solar active Ag/ZnO nanostructured arrays obtained by a combination of electrochemical and chemical methods

The work is devoted to the creation and research of solar active Ag/ZnO nanostructured arrays obtained by a combination of electrochemical and chemical methods. In order to enhance a solar activity of the electrodeposited in a pulsed mode nanostructured zinc oxide arrays and Ag/ZnO nanocomposites thereon we analyzed morphology, structure, electrical, electronic and optical properties of the electroplated 1-D ZnO as well as Ag nanoparticles, deposited from silver sol and Ag/ZnO nanocomposites formed by applying Ag nanoparticles to the ZnO surface. The investigated electrical and electronic parameters of ZnO and Ag/ZnO, which we obtained from their current–voltage and capacitance–voltage characteristics, are the electrical resistivity ρ, the height φ of the Schottky barriers in the electron depletion regions, the concentration of the fully ionized donor impurity Nd, the density NSS of surface states and the width of the electron depletion region ω. The improved UV sensitivity of the electrodeposited in the pulsed mode 1-D ZnO and enhanced solar activity of Ag/ZnO were valued by dark and light current–voltage characteristics and through their temporal response curves under the influence of UV and visible sunlight. Analysis of electronic and electrical parameters, response and recovery performance of the obtained 1-D ZnO arrays and Ag/ZnO nanocomposites thereon let us to select the optimum manufacturing conditions for the creation of solar active plasmonic Ag/ZnO nanostructured arrays with high photosensitivity, fast response and reset times, and reproducible characteristics. So, our studies have allowed the development of a new solar active Ag/ZnO material for photocatalytic oxidation–reduction processes that can be used as photoelectrode for photocatalytic degradation of organic contaminations or for green hydrogen production by water splitting.

THE PROCESSES ASSOCIATED WITH THE BIFURCATION IN THE CURRENT-VOLTAGE CHARACTERISTICS

The mechanisms leading to the intersection of the dark and light current-voltage characteristics and related phenomena has been considered. The possibility of participation in it as non-equilibrium carriers in the case of solar cells, and the contribution of the equilibrium charge when the temperature impact on the reference diode has been shown. Models explaining the observed features has been built.

Evaluation of concentrator photovoltaic properties of GaInNAsSb solar cells for multijunction solar cell applications

In this work, we focus on the growth and characterization of undoped GaInNAsSb layers in solar cells and also study their concentrator photovoltaic properties. Concentrated light current–voltage characteristics of three GaInNAsSb-based solar cells with various thicknesses of GaInNAsSb layers (ti) from 1.0 to 3.0 µm were evaluated. The photogenerated carriers from the GaInNAsSb layers are well collected even for the ti = 2.0 and 3.0 µm devices. The comparison of the solar cell parameters under high concentration conditions showed no significant difference among the devices. This behavior is consistent with the results of series resistance analyses. This suggests that the bulk resistance due to the GaInNAsSb thickness is a minor factor for the series resistance in the present devices.

Optimal Fabrication of P3HT:PCBM Based Organic Solar Cells with N-Type DMDCNQI Dopant.

We have fabricated P3HT and PCBM-based organic photovoltaic cells using DMDCNQI as a guest dopant material and an n-type buffer layer. We have investigated the physical effects of the DMD-CNQI molecule as a guest dopant and an n-type charge transfer buffer layer on the performance of the device by examining measurements of light current-voltage and photoluminescence characteristics. The device using DMDCNQI as a dopant and a buffer layer exhibited a remarkable increase in short-circuit current density (Jsc) due to the ability of an electron acceptor and to the formation of a highly conducting charge transfer complex. In particular, the device consisting of ITO/PEDOT:PSS/P3HT:PCBM:DMDCNQI(1 wt%)/DMDCNQ/Al showed a maximum power conversion efficiency of 3.50%.

Study of degradation of photovoltaic cells based on A3B5 nanoheterostructures under ionizing radiation

Solar radiation is a practically inexhaustible and environmentally friendly source of energy. Solar panels are classified as devices very sensitive to radiation. Therefore, the problem of creating radiation-resistant solar panels is quite acute. In operation, solar batteries (SB) are exposed to hard corpuscular radiation (radiation belts, solar and cosmic radiation), resulting in the structure of accumulated violations leading to a gradual deterioration of their electrical characteristics.We have conducted experimental studies of single-degradation characteristics of solar cells (SE) based on GaAs with Ge substrate due to the structural damage produced by irradiation with fast neutrons and electrons and step-by-step irradiation with fast neutrons and electrons at different fluences. Before and after each set of neutron and electron fluence we have measured light current–voltage characteristics (CVC) and photosensitivity spectra of the AOC. We have determined the following parameters from the measured CVC: the fault current, the open circuit voltage, the maximum coefficient of performance (COP) (ratio of maximum power to the product of the flux density of solar energy and the cell area) and the fill factor (the ratio of maximum power to the product of the short-circuit current and voltage idling).

Analysis of Fine-Line Screen and Stencil-Printed Metal Contacts for Silicon Wafer Solar Cells

Primary challenges to fine-line silver printing for solar cells are achieving high aspect ratios and uniform lines with a low level of striations. This paper compares two high-throughput printing technologies, namely, printing by screens versus stencils. A statistical method is introduced to evaluate the quality of the printed front grid based on the distributions of printed metal line profiles, line segment conductance, overall electroluminescence (EL) pattern, and solar cell light current-voltage (I-V) characteristics. The model distribution, combined with finite-element modeling to predict realistic cell-level voltage variations, adequately describes all four kinds of characteristics. It predicts well the diverging performance of screen- and stencil-printed solar cells as the line width becomes less than 50 μm. Experimentally, the highest batch average efficiency of 18.8% was achieved on 156 mm × 156 mm p-type monocrystalline silicon solar cells printed with stencils having 30-μm line openings, using only 78 mg of silver paste per cell.

Injection photodiode based on a p-Si-n-CdS-n +-CdS structure

An injection photodiode with a high room-temperature rectification factor (105) is developed based on a p-Si-n-CdS-n +-CdS structure. It is shown that the light and dark current-voltage characteristics of the structure have identical features. It is found that the mode of “long” diodes is implemented in the structure at current densities of I = 10−2−5 × 10−4 A/cm2; in this case, the integral (S int) and spectral (S λ) sensitivities sharply increase. It is shown that S int = 2.8 × 104 A/lm (3 × 106 A/W) for an illuminance of E = 0.1 lux and S λ = 2.3 × 104 A/W under laser irradiation with λ = 625 nm and a power of P = 10 μW/cm2 at a bias voltage of V = 20 V. It is shown that the mechanism of photocurrent amplification is predominantly associated with ambipolar carrier-mobility modulation.

On the role of metal contacts in solar cells based on titanium dioxide and di-(isothiocyanate)-bis-(2,2′-bipyridyl-4,4′-dicarboxylate)ruthenium(II)

Photoelectric cells based on titanium dioxide and di-(isothiocyanate)-bis-(2,2′-bipyridyl-4,4′-dicarboxylate)ruthenium(II) with titanium and gold electrodes are fabricated. An analysis of the dark and light current-voltage characteristics shows that the electrode material affects the main parameters of the solar cells: the open-circuit voltage, short-circuit current, and efficiency.

Transport and luminescence phenomena in electroformed silicon nitride-based light emitting diode

Hydrogenated amorphous silicon nitride-based heterojunction pin diode was electroformed under sufficiently high forward bias stress leading to its instant nanocrystallization at room temperature. In order to investigate the origin of the accompanying bright visible light emission, current-voltage and electroluminescence (EL) characteristics of the electroformed diode were scanned over temperature. Electrical transport mechanism was analysed in the low, medium and high electric field regimes. Temperature and field dependence of thermal activation energy were discussed. EL characteristics were studied using the spectral energy distribution and the injection current dependence of its intensity. Thermal quenching data of EL and photoluminescence intensities were compared. Finally, the relationship between the electrical transport and luminescence phenomena was attempted to be interpreted within the frame of a self-consistent model.

Radiation detectors based on Multiwall Carbon Nanotubes deposited by a spray technique

In this paper a study of Multi Wall Carbon Nanotube films deposited at low temperature by means of a spray technique on different substrates is presented. Nanodispersion of nanotube powder in a non-polar 1,2-dichloroethane solvent was used as starting solution. Electron Microscopy in Scanning and Transmission modes were used in order to verify the morphological properties of the deposited films.Visible light detectors were prepared spraying Multi Wall Carbon Nanotubes on silicon substrates with different layouts. In some detectors the nanotubes were covered by an Indium Tin Oxide (ITO) layer. Electrical measurements, both in dark and under light irradiation, were performed and Current-Voltage characteristics are reported. The Indium Tin Oxide coating effect on the photoconductivity yield is presented and discussed along with device ageing test, resulting in a very good photoconduction and stability over four months.

Fabrication and characterization of CuO/ZnO solar cells

Cuprous oxide (CuO) and zinc oxide (ZnO) heterojunction solar cells fabricated on indium tin oxide-coated glass were studied. CuO and ZnO films were deposited using a galvanostatic method. Structural, morphological and optoelectronic properties of the CuO/ZnO heterojunction were studied by using X-ray diffraction, atomic force microscopy and light current-voltage characteristics.

Fabrication and theoretical analysis of GaN-based vertical light-emitting diodes with SiO2 current blocking layer

We report the fabrication and characteristics of 1 × 1 mm2 blue vertical light-emitting diodes (VLEDs) with a SiO2 current blocking layer (CBL), together with their theoretical analysis in terms of electrical, optical and thermal properties. The SiO2 CBL improves the total light extraction efficiency by relieving the current crowding under the metal n-electrode. Additionally, the total light extraction efficiency of LEDs with SiO2 CBL remains almost the same independent of injection current, whereas that of conventional VLEDs is gradually decreased with injection current. The optical output power (Pout) for the VLED with SiO2 CBL is increased by about 10% at 350 mA in a wafer level without serious degradation in operating voltage resulting from the insertion of SiO2 CBL, thus resulting in a high Pout of 670 mW at 950 mA. The simulated light–current–voltage characteristics of the fabricated devices were reasonably consistent with the measured results.

Features of the light current-voltage characteristics of bifacial solar cells based on thin CdTe layers

It is shown that the features of the illuminated current-voltage characteristics of bifacial solar cells glass/SnO2:F/CdS/CdTe/Cu/ITO with a thin base layer are associated with the photovoltaic effect at the back contact. An equivalent circuit of the device structure under study, which takes into account the existence of two illuminated diodes—a frontal diode (main separating barrier) and a diode at a back contact—is suggested.

Fabrication of the CuO/Cu2O heterojunction using an electrodeposition technique for solar cell applications

Thin films of n-type cuprous oxide (Cu2O) were potentiostatically electrodeposited on a Ti substrate in an acetate bath. Cu2O thin films were annealed at 500 °C for 30 min in air for growing p-type cupric oxide (CuO) thin films. n-Cu2O thin films were potentiostatically electrodeposited in an acetate bath on Ti/CuO electrodes in order to fabricate the p-CuO/n-Cu2O heterojunction. The structural, morphological and optoelectronic properties of the CuO/Cu2O heterojunction were studied using x-ray diffraction (XRD), scanning electron micrographs (SEMs) and dark and light current–voltage characteristics. XRD and SEM reveal that well-covered single phase polycrystalline Cu2O thin film on the Ti/CuO electrode can be possible at the deposition potential of −550 mV versus the saturated calomel electrode (SCE) in an acetate bath. Photovoltaic characteristics further established the formation of the CuO/Cu2O heterojunction.

Specific features of light current-voltage characteristics of p-i-n structures based on amorphous silicon in the case of the tunnel-drift mechanism of dark current transport

Current-voltage (I–V) characteristics of p-i-n structures based on amorphous silicon (α-Si:H) with small hole diffusion lengths (shorter than the thickness of the i-layer of a p-i-n structure) have been experimentally studied with and without illumination. It is shown that forward I–V characteristics of structures of this kind can be described by a dependence inherent in diodes, with a diode ideality factor two-three times the maximum value of 2, theoretically predicted for generation-recombination currents in p-n junctions. The dark current is always substantially lower than the photocurrent in a cell biased with a voltage approximately equal to the opencircuit voltage of the photocell. Dark currents cannot contribute to the I–V characteristic under illumination. The photocurrent decreases with increasing photovoltage at a bias lower than the open-circuit voltage because of a decrease in the collection coefficient and the increasingly important role of back diffusion of electrons into the p-contact, rather than as a result of the dark injection. In the case of biases exceeding the open-circuit voltage, back diffusion becomes the predominant component of the current.

Franz–Keldysh Photon-Assisted Voltage-Operated Switching of a Transistor Laser

Data are presented on the transistor laser light-output (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I-V </sub> ) as a function of base current and the collector-to-emitter voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CE</sub> ) revealing sensitive fine structure that can, with suitable bias, be exploited for signal switching and mixing. The output light intensity versus current-voltage characteristics (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I-V </sub> ) and the fine structure in the L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I-V</sub> characteristics are related to the change in laser operation from the ground state to the first excited state of the quantum well incorporated in the transistor base, laser mode changes, or shift from spontaneous to stimulated emission (or the reverse). The region of stimulated recombination and its boundary are or particular interest. The concept of the voltage-driven switching of a transistor laser employing the Franz-Keldysh photon-assisted process to shift the operation from stimulated (high coherent optical field) to spontaneous (lower incoherent field) is demonstrated