Photocurrent Characteristics Research Articles

Facile one-pot synthesis of photoresponsive Cu1.8S and CuInS2 nanostructures aided by Cu-pyrimidylthiolate molecular precursor

Copper-based binary and ternary sulfides have attracted significant attention due to their excellent photo-physical properties, making them highly promising for high-performance energy harvesting and storage devices. This study focuses on the synthesis and structural characterization of an air-stable hexanuclear Cu-pyrimidylthiolate cluster complex which serves as an efficient single-source precursor for the preparation of Cu1.8S nanocrystals. Furthermore, coupling the molecular precursor with suitable indium source resulted in a facile one-pot pathway for the preparation of technologically important, copper-based ternary CuInS₂, nanocrystals. The crystal structure, phase purity, and compositions of the nanostructures were confirmed using PXRD, XPS, EDS, and area elemental mapping. Electron microscopic studies revealed the formation of polygonal and hexagonal morphology with varied size in Cu1.8S and CuInS₂ nanocrystals respectively. UV-Vis diffuse reflectance spectroscopy showed a slight blue shift in the band gap of the nanostructures compared to their bulk counterparts which can be attributed to quantum confinement or surface lattice distortion effects. The band gap of the pristine nanocrystals along with high photocurrent and stable photo-switching characteristics suggest that they can serve as suitable electrode material for optoelectronic and photodetector devices.

Charge separation by switching heterojunction system from Type-II to S-scheme for enhanced photocatalytic activity: Environmental detoxification and H2 production

The development of highly efficient photocatalysts is essential for harnessing solar energy for pollutant degradation and hydrogen (H2) production. This study provides a novel ternary S-scheme photocatalyst (Fe2O3/Bi2O3/g-C3N4), prepared from optimized binary 20-Bi-C via a simple electrostatic self-assembly method for the first time. Using various methods including UV–vis DRS, PL, ESR, photocurrent, Mott-Schottky, XPS, XRD, FTIR, SEM, TEM, and BET, the optical, structural, and morphological characteristics of the produced materials were fully studied. The photocatalytic performance of as-manufactured materials was evaluated through the degradation of the Ciprofloxacin (CIP) and H2 production. Under optimized conditions determined by the RSM method, a maximum CIP degradation of 97.20 % was achieved at a rate of 0.053 min−1, with the catalyst dosage: 0.44 g/l, CIP concentration: 26.07 mg/l, pH: 6.29 and Time: 63.01. The optimized heterojunction exhibited an exceptional photocatalytic H2 generation rate of 2428 μmol·g−1·h−1 within 2 h, surpassing the binary 20-Bi-C photocatalyst by 1.3 times. Furthermore, after five continuous cycles, the 5-Fe2O3/Bi-C photocatalyst showed good chemical stability and reusability, sustaining a degradation rate of over 96 % and a TOC removal of 80 %. Experiments on the identification of free radicals have demonstrated the important roles that O2−, h+, and OH species play in the photocatalytic process. The enhancement mechanism of 5-Fe2O3/Bi-C involves the successful synthesis of Fe2O3/Bi-C photocatalyst with well-aligned positions of band gap edges, enabling the facile charge transfer through S-Scheme mechanism. Furthermore, the study investigates the impact of environmental factors, including solution pH, water matrices, and the efficiency of the synthesized photocatalyst on other organic pollutants. The photocatalytic degradation behavior of CIP is predicted using LC-MS analysis. This work provides a new method for building S-scheme heterojunctions by creatively converting the type-II heterojunction system to an S-scheme by metal oxide doping.

Photoresponse properties of green-assisted Fe3O4 nanoparticles supported activated carbon

The photoresponse properties of green synthesized Fe3O4 (gFe3O4) supported-activated carbon (AC/g-Fe3O4) were studied using a photocurrent characterization approach. Preliminary UV–Vis analysis suggested a reduction in the band gap energy when activated carbon is incorporated into gFe3O4 nanoparticles (2.61 → 1.57 eV). The current-voltage characteristics indicate semiconductor features for both gFe3O4 and AC/gFe3O4 nanoparticles. The photodetector measurements indicate a significantly enhanced response for AC/gFe3O4 and can be attributed to increased rectification and photogenerated carriers emanating from the activated carbon incorporation. The study proposes AC/gFe3O4 nanocomposite as a novel material that can be used for the fabrication of photodetectors and other related optoelectronic devices.

High polarization sensitivity passive spin Photogalvanic devices based on 2D perovskite CsMnBr4/CsSbCl3Br/CsMnBr4 heterojunction

In recent years, Dion-Jacobson (D-J) perovskite has been extensively studied. In order to further study the application of D-J perovskite materials in spin-optoelectronic multifunctional devices, this paper is based on CsSbCl3Br and CsMnBr4, a zero-band gap semi-metallic material with the same ferromagnetic ground state and the same crystal structure. In this paper, put forward with transverse CsMnBr4/CsSbCl3Br/CsMnBr4 heterojunction optoelectronic devices. The characteristics of photocurrent are discussed using parallel configuration (PC) and anti-parallel configuration (APC) magnetoelectric poles under two conditions: vertical incidence of linearly polarized light and elliptically polarized light utilizing density functional theory and the non-equilibrium Green’s function method. The results reveal that the device can achieve complete spin polarization photocurrent, pure spin current, perfect spin filtering effect, and excellent spin valve effect, with high extinction ratios. Under linearly polarized light, the maximum extinction ratio reaches 2747 for the PC configuration and 5200 for the APC configuration. For elliptically polarized light, the extinction ratio is 739 for the PC configuration and reaches a maximum of 240 for the APC configuration. These results indicate that the lateral CsMnBr4/CsSbCl3Br/CsMnBr4 heterojunction has broad multi-functional application prospects in the field of optoelectronics and spintronics.

Acceleration of Photoinduced Electron Transfer by Modulating Electronegativity of Substituents in Stable Zr-Metal-Organic Frameworks to Boost Photocatalytic CO2 Reduction.

Photoreduction of CO2 with water into chemical feedstocks of fuels provides a green way to help solve both the energy crisis and carbon emission issues. Metal-organic frameworks (MOFs) show great potential for CO2 photoreduction. However, poor water stability and sluggish charge transfer could limit their application. Herein, three water-stable MOFs functionalized with electron-donating methyl groups and/or electron-withdrawing trifluoromethyl groups are obtained for the CO2 photoreduction. Compared with UiO-67-o-CF3-CH3 and UiO-67-o-(CF3)2, UiO-67-o-(CH3)2 achieves excellent performance with an average CO generation rate of 178.0 μmol g-1 h-1 without using any organic solvent or sacrificial reagent. The superior photocatalytic activity of UiO-67-o-(CH3)2 is attributed to the fact that compared with trifluoromethyl groups, methyl groups could not only elevate CO2 adsorption capacity and reduction potential but also promote photoinduced charge separation and migration. These are evidenced by gas physisorption, photoluminescence, time-resolved photoluminescence, electrochemical impedance spectroscopy, transient photocurrent characteristics, and density functional theory calculations. The possible working mechanisms of electron-donating methyl groups are also proposed. Moreover, UiO-67-o-(CH3)2 demonstrates excellent reusability for the CO2 reduction. Based on these results, it could be affirmed that the strategy of modulating substituent electronegativity could provide guidance for designing highly efficient photocatalysts.

Impact of deposition temperature on persistent photoconductivity of SnO2 thin films deposited using spray pyrolysis technique suitable in optoelectronic synaptic devices

In this study, nanocrystalline tin oxide thin films that exhibited enhanced persistent photoconductivity (PPC) were prepared using spray pyrolysis technique. The effect of deposition temperature on different aspects of photoconductivity of these films were analysed using different characterization techniques. Raman analysis confirmed the tetragonal rutile structure of the films and also indicated their nanocrystalline nature, while XPS analysis verified the presence and oxidation states of tin and oxygen in the films. The films demonstrated UV sensing capability under above-bandgap illumination, generating electron-hole pairs and enhancing electrical conductivity. The deposition temperature of the film influenced their photocurrent characteristics, showcasing varied responses in terms of photosensitivity and photocurrent. Enhancement of photoresponse was observed with the increase in deposition temperatures of the samples. Notably, films deposited at 450 and 500 °C exhibited the more persistent photocurrent at the tested deposition temperatures. The surface defects, oxygen vacancies and grain boundaries played a significant role in sustaining PPC by ionizing vacancies and creating persistent carriers even after light exposure by trapping free carriers and impeding recombination. From the exponential fitting and extrapolation of the decay curves, the sample prepared at 450 °C was observed to be the most suitable film in application point of view for fabricating devices that make use of persistent photoconductivity. Overall, this work highlights the effectiveness of modulation of deposition temperature in influencing photoconductor parameters of spray pyrolyzed tin oxide films, offering potential applications in non-volatile memory, bionic optoelectronics, neuromorphic computing and bioelectronics.

Electric-field tunable Type-I to Type-II band alignment transition in MoSe2/WS2 heterobilayers

Semiconductor heterojunctions are ubiquitous components of modern electronics. Their properties depend crucially on the band alignment at the interface, which may exhibit straddling gap (type-I), staggered gap (type-II) or broken gap (type-III). The distinct characteristics and applications associated with each alignment make it highly desirable to switch between them within a single material. Here we demonstrate an electrically tunable transition between type-I and type-II band alignments in MoSe2/WS2 heterobilayers by investigating their luminescence and photocurrent characteristics. In their intrinsic state, these heterobilayers exhibit a type-I band alignment, resulting in the dominant intralayer exciton luminescence from MoSe2. However, the application of a strong interlayer electric field induces a transition to a type-II band alignment, leading to pronounced interlayer exciton luminescence. Furthermore, the formation of the interlayer exciton state traps free carriers at the interface, leading to the suppression of interlayer photocurrent and highly nonlinear photocurrent-voltage characteristics. This breakthrough in electrical band alignment control, interlayer exciton manipulation, and carrier trapping heralds a new era of versatile optical and (opto)electronic devices composed of van der Waals heterostructures.

Microsphere structure enhances the photocatalytic performance of TiO2-CdS heterojunction

Herein, a novel TiO2 microsphere structure (TMS) was reported for the first time, formed through the self-assembly of TiO2 nanocone monomers. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis revealed that the microsphere structure substantially boosted the growth density of TiO2 nanocone monomers, facilitating CdS loading. Photocurrent characterization revealed that CdS/TMS heterojunction (CTMS) exhibited a heightened photocurrent response than that of our previously reported CdS/TiO2 nanocone arrays (CTNC), suggesting that the microsphere structure enhanced photon absorption and electron-hole pair transmission channels for TiO2-CdS heterojunctions per unit area. Photocatalytic degradation experiments of tetracycline (TC) demonstrated that CTMS exhibited superior performance, achieving the degradation of 84.9 % of TC within 45 min, high than that of our previously reported CTNC (69.9 %). First-order kinetic fitting indicated that the degradation kinetic constant of CTMS (0.042 min−1) was 1.45 times higher than that of our previously reported CTNC (0.029 min−1).

Analytical modeling of photocurrent in double perovskite Cs[formula omitted]AgBiBr[formula omitted] X-ray detectors

This work has developed a theoretical model to investigate the mechanisms of nonlinear steady-state photocurrent versus dose rate characteristics in Cs2AgBiBr6-based X-ray detectors. The photocurrent analysis on Cs2AgBiBr6-based X-ray detector shows that there is a photocurrent gain, primarily due to the presence of dark current. Charge injection from metal contacts is the primary source of dark current in Cs2AgBiBr6. The accumulation of X-ray induced ions near the electrodes elevates the metal/perovskite interface electric field, and hence increases the charge injection with the X-ray dose. The Schottky barrier height for charge injection is found to be dependent on the X-ray dose as well. Therefore, the variation of dark current under X-ray exposures are mainly responsible for the non-linear steady-state photocurrent. The comparison of the model with the experimental results reveals the accumulated ion concentrations and effective barrier heights.

A study on the dark and illuminated operation of Al/Si3N4/p-Si Schottky photodiodes: optoelectronic insights

This work extensively investigates the operation of an Al/ Si3N4/p-Si Schottky-type photodiode under dark and varying illumination intensities. The photodiode is fabricated by employing the metal–organic chemical vapor deposition (MOCVD) method. A thorough electrical characterization is performed at room temperature, encompassing measurements of current–voltage (I–V), current–time (I–t), capacitance–time (C–t), and conductance time (G–t). The photodiode’s rectification factor and reverse bias area increased under illumination. The relationship between light power density, barrier height, and diode ideality factor is found. The study also found a strong correlation between light intensity and applied voltage on series resistance (Rs) and shunt resistance (Rsh). Rs values are calculated using Cheung’s functions, revealing the diode’s resistance behavior. The study also examines the photodiode’s photoconductivity and photoconductance, finding a non-linear relationship between photocurrent and illumination intensity, suggesting bimolecular recombination. Calculated photosensitivity (K), responsivity (R), and detectivity (D*) values show the device’s light response effectiveness, but efficiency decreases at higher illumination intensities. Transient experiments indicate stable and reproducible photocurrent characteristics, revealing photogenerated charge temporal evolution. This study provides a complete understanding of the Al/Si3N4/p-Si Schottky photodiode’s behavior under different illumination intensities. The findings advance optoelectronic device knowledge and enable their use in advanced technologies.

Gate controllable fully spin-polarized and pure spin current in γ-graphyne nanoribbon

Gate-controlled spin-dependent transport has paved the way for spintronic devices with tunable functionalities. In this study, we calculated the spin-dependent transport properties and photocurrent characteristics of a two-probe device based...

Low dose indirect conversion X-ray sensors based on Cs3Cu2I5 and CsPbBr3 coated BPW-34 photodiode

Metal halide perovskites (MHPs) have demonstrated tremendous applicability in optoelectronic research owing to their fascinating properties and extensive range of crystal structures. Among the MHPs, cesium copper iodide (Cs3Cu2I5) and cesium lead bromide (CsPbBr3) have been utilized in numerous applications like photovoltaics, photodetectors, and scintillation detectors. In this report, we present a cost-effective approach to developing an indirect conversion X-ray sensor based on Cs3Cu2I5 and CsPbBr3, utilizing a commercial photodiode (BPW 34). The MHPs were synthesized by solid-state exchange reaction, dissolved in dimethyl formamide (DMF), and recrystallized within a polymer matrix. The MHP polymer matrix was then coated onto the top surface of the photodiodes as thick films. The photocurrent characteristics of Cs3Cu2I5 and CsPbBr3 indirect X-ray sensors, upon exposure to X-rays at 70 kVp energy under various X-ray exposures and zero bias conditions, were recorded. Both MHPs exhibited a significant response to the incident X-rays. These outcomes highlight the potential of Cs3Cu2I5 and CsPbBr3 scintillators for fabricating X-ray imagers based on commercial photodiode arrays.

Photovoltage and Photocurrent Absorption Spectra of Sulfur Vacancies Locally Patterned in Monolayer MoS2.

We report on the optical absorption characteristics of selectively positioned sulfur vacancies in monolayer MoS2, as observed by photovoltage and photocurrent experiments in an atomistic vertical tunneling circuit at cryogenic and room temperature. Charge carriers are resonantly photoexcited within the defect states before they tunnel through an hBN tunneling barrier to a graphene-based drain contact. Both photovoltage and photocurrent characteristics confirm the optical absorption spectrum as derived from ab initio GW and Bethe-Salpeter equation approximations. Our results reveal the potential of single-vacancy tunneling devices as atomic-scale photodiodes.

Morphological, structural, optical and photocurrent characteristics of Bi(TixMn(1-x))O3 perovskite nanorods grown by hydrothermal synthesis

This study focuses on the hydrothermal synthesis of Bi(TixMn(1-x))O3 (x = 0.3–0.9) perovskite nanorods on fluorine-doped tin oxide glass substrates and investigates the influence of Ti4+ on their morphological, structural, optical properties, and photocatalytic behavior. The high-resolution XPS spectra results have proved that Ti has been properly substituted into the Bi(TixMn(1-x))O3 nanorods. The characterization of morphology reveals a decrease in average diameter from 222 to 115 nm as the Ti concentration increases, while the band-gap energy experiences a slight reduction from 3.158 to 3.132 eV. X-ray and Raman spectroscopy analyses of the Bi(TixMn(1-x))O3 nanorods indicate that Ti ions substitute not only Mn3+ but also Bi3+ ions, leading to structural distortions in the crystal lattice. Moreover, the Bi(TixMn(1-x))O3 systems demonstrate enhanced photocurrent densities at 1.5 V potential, ranging from 3.19 to 5.54 mA/cm2, as the Ti concentration increases. This enhancement can be attributed to the combined effects of increased surface area, accelerating electron transfer at the interface of the electrode, and decreased optical band-gap energy. It is anticipated that this novel system will pave the way for further advancements in the field of photocatalytic water splitting and solar energy conversion applications.

Photonic synaptic transistors with new electron trapping layer for high performance and ultra-low power consumption

Photonic synaptic transistors are being investigated for their potential applications in neuromorphic computing and artificial vision systems. Recently, a method for establishing a synaptic effect by preventing the recombination of electron–hole pairs by forming an energy barrier with a double-layer consisting of a channel and a light absorption layer has shown effective results. We report a triple-layer device created by coating a novel electron-trapping layer between the light-absorption layer and the gate-insulating layer. Compared to the conventional double-layer photonic synaptic structure, our triple-layer device significantly reduces the recombination rate, resulting in improved performance in terms of the output photocurrent and memory characteristics. Furthermore, our photonic synaptic transistor possesses excellent synaptic properties, such as paired-pulse facilitation (PPF), short-term potentiation (STP), and long-term potentiation (LTP), and demonstrates a good response to a low operating voltage of − 0.1 mV. The low power consumption experiment shows a very low energy consumption of 0.01375 fJ per spike. These findings suggest a way to improve the performance of future neuromorphic devices and artificial vision systems.

Synergistic effect of AgBiS2 segregated NaV3O8 nanostructures in direct conversion X-ray sensors

Synergistic nanostructures possess enriched electrical and optical properties compared to conventional nanostructures. 1D-3D synergized nanostructure was implied to elucidate the performance of the X-ray sensor for the first time. Current research in X-ray detection only focuses on implementing high attenuating material based on oxides/ perovskites in developing X-ray sensors. Herein we approached tailoring the performance of an X-ray sensor with a synergistic nanostructure composed of sodium vanadium oxide (NaV3O8) with substantial grain boundary (GB) segregation of silver bismuth sulfide (AgBiS2), enabling the structured arrangement of nanostructured grains at the surface of NaV3O8 nanorods. Then, it was coated as a thick film on top of the interdigitated electrodes by glass rod sliding technique to readout the dose-dependent X-ray sensing capability. From the X-ray impinged photocurrent characteristics, the sensor with 75 wt% AgBiS2 segregated NaV3O8 exhibits superior sensitivity 82.6 nC mGy-1 cm-2 and low-noise equivalent dose rate 1.04 mGy Hz-0.5 for 2.49 mGy s-1 than other compositions. These experimental findings explore the implication of synergistic nanostructures as active layers in direct conversion X-rays sensors for improved charge extraction and enhancement in X-ray impinged photocurrent at low dose rates.

Optimization of Si photocathode formation conditions through correlation between saw damage removal and black Si

This study aimed to address the correlation between the saw damage removal (SDR) process and the formation of a nanoporous structure in order to fabricate a phototoelectrochemical (PEC) water splitting photocathode using silicon (Si) wafer utilized in solar cell. The experimental conditions were categorized into two groups: 1) before and after SDR process, and 2) the nanoporous structure formation time (ranging from 1 to 10 min) to identify the optimized conditions for enhancing efficiency. The results showed that the Si photocathode manufactured with a nanoporous structure fabricated for 5 min after SDR process had the lowest reflectance and interfacial defect, and the highest photocurrent density. This is because saw damage on the wafer caused many defects on the surface, making it difficult to form a uniform nano-porous structure. The SDR process helped in eliminating the saw damage and creating a uniform Si surface. In addition, the uniform nanoporous structure facilitated substantial light absorption, leading to the creation of numerous electrons and hole pairs, and resulted in achieved high efficiency by providing smoother the movement of carriers due to low interfacial defects. In summary, this study established a correlation between the SDR process and the formation of a nanoporous structure in the manufacturing of Si wafer for solar cells as a photocathode, and confirmed that the uniform nanostructure remarkably improves the photocurrent density characteristics.

Nanoscale Characterization of Photocurrent and Photovoltage in Polycrystalline Solar Cells.

We investigate the role of grain structures in nanoscale carrier dynamics of polycrystalline solar cells. By using Kelvin probe force microscopy (KPFM) and near-field scanning photocurrent microscopy (NSPM) techniques, we characterize nanoscopic photovoltage and photocurrent patterns of inorganic CdTe and organic-inorganic hybrid perovskite solar cells. For CdTe solar cells, we analyze the nanoscale electric power patterns that are created by correlating nanoscale photovoltage and photocurrent maps on the same location. Distinct relations between the sample preparation conditions and the nanoscale photovoltaic properties of microscopic CdTe grain structures are observed. The same techniques are applied for characterization of a perovskite solar cell. It is found that a moderate amount of PbI2 near grain boundaries leads to the enhanced photogenerated carrier collections at grain boundaries. Finally, the capabilities and the limitations of the nanoscale techniques are discussed.

Current, photocurrent and thermocurrent of borophene-black phosphorus heterostructures

In this paper, we calculated current–voltage characteristic curves (IV curves), Conductivity, real space charge distribution, transmission spectrum, photocurrent, and thermal current of the borophene-black phosphorus heterostructure. Our results show that the zigzag device has excellent photocurrent characteristics. The direction of photocurrent can be adjusted by changing the wavelength of incident light and adding gate voltage. The armchair device has excellent IV curve characteristics and good linear characteristics at low voltage. The armchair device also has good thermoelectric current properties. The position distribution of covalent bonds formed between atoms in this heterostructure is revealed by the real space charge distribution. Our results are significant for applying borophene-black phosphorus heterostructure in electric transport devices.

Influence of applied bias on direct conversion X-ray sensing capability of nanocrystalline Ca9Ag(PO4)6(OH)2

Silver (Ag) doping in hydroxyapatite (HAP) can enhance the attenuation coefficient (μ) 0.65 cm2/g at photon energy 70 keV as compared with pure hydroxyapatite (μ = 0.31 cm2/g). In this study, direct conversion X-ray sensors were fabricated using pure HAP (Ca10(PO4)6(OH)2) and Ag-doped HAP (Ca9Ag(PO4)6(OH)2) to realize superior X-ray sensing capability. Thick films of wet-chemical route derived nanocrystalline samples were deposited on interdigitated electrodes by glass rod sliding technique and its X-ray instigated photocurrent characteristics at 2 V biased condition were recorded for different low doses (mGy). The observed sensitivity at 7.97 mGy dose reveals ten folds enhancement from 0.19 nC/mGy cm3 to 1.00 nC/mGy cm3. According to the “Grain boundary double Schottky potential barrier height model”, the formation of potential barrier height (φb) at the interface of grain and grain boundaries of nanocrystalline samples is identical to the Schottky barrier. By increasing the applied bias, the conduction band starts to bend and suppresses the potential barrier height (φb). In higher biased conditions, φb does not exist. Hence, the influence of applied bias on direct conversion X-ray sensing capability of Ca9Ag(PO4)6(OH)2 was investigated and discussed in detail.