Photocurrent-time Curves Research Articles

Enhancing Photoelectric Response of Self-powered UV and Visible Detectors Using CuO/ZnO NRs Heterojunctions.

Understanding the development and performance of UV photodetectors is crucial, given their extensive applications in both military and civilian sectors. The evolution of self-powered photodetectors, especially those based on heterojunction nanostructures, has demonstrated significant potential for enhancing both device efficiency and functionality. By exploring the effects of material composition and structural design, can optimize these devices for improved photoelectric response and energy efficiency. In this study, we prepared the CuO/ZnO NRs heterojunction photodetector on an ITO substrate to enhance photoelectric response of UV detectors. The fabrication process utilized the hydrothermal method and the spin coating technique. The effect of CuO concentration on the optical response of the photodetector under UV radiation at wavelengths of 405nm and 385nm was investigated. The samples were characterized using FESSEM, XRD, EDX, and UV-Vis spectra. The device is further distinguished by its standard I-V curves and photocurrent-time curves, which demonstrate the device's behavior under various light conditions. The prepared thin films are polycrystalline, with CuO layers displaying monoclinic phases and ZnO layers exhibiting a hexagonal wurtzite phase. All samples have the potential to exhibit photovoltaic properties and self-powered capabilities. Furthermore, the I-V curve confirms that the photocurrent mechanism of these junctions adheres to the recombination standard, in addition to demonstrating correction behavior. A sample with a CuO concentration of 0.1M shows the highest photosensitivity, reaching 340,700%, and a photocurrent gain (Iph/Idark) of 3,408 when exposed to light irradiation at 405nm. Additionally, it exhibits a rapid response time of 0.8s.

Physics-Based Artificial Neural Network Assisting in Extracting Transient Properties of Extrinsically Triggering Photoconductive Semiconductor Switches.

In this paper, a physics-based ANN assisting method for extracting transient properties of extrinsically triggering photoconductive semiconductor switches (ET-PCSSs) is proposed. It exploits the nonlinear mapping of ANN between transient current (input) and doping concentration (output). According to the basic laws of photoelectric device operating, two types of ANN models are constructed by gaussian and polynomial fitting. The mean absolute error (MAE) of forecasting transient photocurrent can be less than 10 A under low triggering optical powers, which verifies the feasibility of ANN assisting TCAD applied to PCSSs. The results are comparable to computation by Mixed-Mode simulation, yet even thousands of seconds of CPU runtime cost are saved in every period. To improve the robustness of the Poly-ANN predictor, Bayesian optimization (BO) is implemented for minimizing the curl deviation of photocurrent-time curves.

Performance assessment of oxygenated CdS films-based photodetector

CdS films were grown by thermal evaporation on glass substrates. After growth process, samples were oxygenated at 400 °C at various gas pressures for 5 mins employing rapid thermal process. The produced CdS films were used as photodetectors in blue light. X-ray diffraction results revealed that as-deposited CdS films had a wurtzite crystal structure with a satrong preferred orientation along (002) plane. The intensity of (002) peak increased by rising oxygen gas pressure to 2 atm and then decreased with further increase of oxygen gas pressure to 4 atm. Scanning electron microscopy analysis indicated that even though as-deposited CdS thin films included some aligned rod-like grains on an underlaying layer, oxygenation at various gas pressures changed the surface morphology of CdS films. CdS films oxygenated at a gas pressure of 2 atm exhibited the best transmittance value of 80% in the range of 600–1000 nm. It was calculated that band gap increased from 2.42 eV to 2.45 eV as CdS films were oxygenated at a gas pressure of 2 atm. Photoluminescence spectrum of as-deposited CdS films indicated two fundamental peaks located at 530 nm and an interval of 550–700 nm, corresponding to green and deep level emissions, respectively. Consequently, it was attained that CdS films oxygenated at a pressure of 2 atm had the optimized structural, morphological and optical results and therefore, this sample was further employed for photodetecting applications. From photocurrent-time curves, the best photodetecting performance was reached for CdS films-based device oxygenated at a gas pressure of 2 atm including rise time and fall time values of 22 ms and 25 ms, respectively. In addition, the maximum responsivity, detectivity and external quantum efficiency were found to be 23.7 mA/W, 4.75 × 108 Jones and 6.6 for the same photodetector, respectively.

Preparation of rose-like Bi2O2CO3 photocatalyst with enhanced performance for photocatalytic degradation of mineral flotation wastewater

Eight kinds of bismuth oxycarbonate (Bi2O2CO3, BOC) with different microscopic morphology were prepared to study the influence of microscopic morphology on its photocatalytic performance. The crystal structure and microscopic morphology of Bi2O2CO3 were regulated by different synthetic recipes and routes. The SEM and TEM show the samples can be classified into two-dimensional (2D) and three-dimensional (3D) Bi2O2CO3 materials. The BOC-8 possesses a rose-like structure and a specific surface area (SBET) of 44.93 m2/g. In the experiments of degrading mineral flotation agent sodium isobutyl xanthate (SIBX). The photocatalytic performance of 3D samples is generally superior to that of 2D samples, and BOC-8 exhibits the best photocatalytic performance. After 90 min of simulated sunlight irradiation, the degradation ratio of SIBX over BOC-8 is 92.41 %. The transient photocurrent-time curves, electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) spectra show that BOC-8 has excellent photogenerated electron and hole separation efficiency. The degradation pathway of SIBX was explored. And the hydroxyl radicals (OH) is the main active oxygen species for SIBX degrading. The enhanced photocatalytic degradation performance of BOC-8 samples originated from the increase of SBET, improved light utilization and more efficient photogenerated charge separation caused by the formation of 3D structure.

Enhancing catalytic performance of TiO2/P-doped C3N4 composite via preferentially bonded P-O-Ti

Optimizing photocatalyst structure at the atomic level is a crucial challenge in improving photocatalytic performance. Herein, a series of TiO2/P-doped C3N4-pinned composites have been synthesized to optimize photocatalyst structure at the atomic level. Among the nonmetals (P, C, and N) in P-doped C3N4 (CN-P), TiO2 preferentially bonds with P to form stable P-O-Ti chemical bonds that can act as efficient carrier transfer channels. Comprehensive correlations between P-O-Ti bond features, defects, carrier kinetics, and photocatalytic activity have been studied theoretically and experimentally. Photocurrent-time curves and distribution of relaxation times analysis reveals that preferentially bonded P-O-Ti improves carrier separation and transfer. The special P-O-Ti interface bonds endows composites TiO2/P-doped C3N4 with multifunctional photocatalysis properties, i.e., hydrogen production (815 µmol g−1 h−1), and completely reducing heavy metal ions Cr (VI) (10 min ) under visible light (λ > 400 nm) irradiations, which outperforms most of existing CN-P and TiO2 composite catalysts, as well as excellent degradation performance for organic contaminants. More importantly, the composite with optimal composition shows a superior stability and repeatability in ten cycles of testing. These findings provide valuable hints in optimizing photocatalyst structure at the atomic level for enhancing carrier dynamics and improving photocatalytic performance necessary for applications under visible light.

Opto-Electronic Characterization of Photocatalysts Based on p,n-Junction Ternary and Quaternary Mixed Oxides Semiconductors (Cu2O-In2O3 and Cu2O-In2O3-TiO2)

Semiconductor materials are the basis of electronic devices employed in the communication and media industry. In the present work, we report the synthesis and characterization of mixed metal oxides (MOs) as p,n-junction photocatalysts, and demonstrate the correlation between the preparation technique and the properties of the materials. Solid-state UV-visible diffuse reflectance spectroscopy (UV-VIS DRS) allowed for the determination of the light absorption properties and the optical energy gap. X-ray photoelectron spectroscopy (XPS) allowed for the determination of the surface speciation and composition and for the determination of the valence band edge. The opto-electronic behavior was evaluated measuring the photocurrent generated after absorption of chopped visible light in a 3-electrode cell. Scanning electron microscopy (SEM) measurements allowed for auxiliary characterization of size and morphology, showing the formation of composites for the ternary Cu2O-In2O3 p,n-mixed oxide, and even more for the quaternary Cu2O-In2O3-TiO2 MO. Light absorption spectra and photocurrent-time curves mainly depend upon the composition of MOs, while the optical energy gap and defective absorption tail are closely related to the preparation methodology, time and thermal treatment. Qualitative electronic band structures of semiconductors are also presented.

A kinetic model for redox-active film based biophotoelectrodes.

Redox-active films are advantageous matrices for the immobilization of photosynthetic proteins, due to their ability to mediate electron transfer as well as to achieve high catalyst loading on an electrode for efficient generation of electricity or solar fuels. A general challenge arises from various charge recombination pathways along the light-induced electron transfer chain from the electrode to the charge carriers for electricity production or to the final electron acceptors for solar fuel formation. Experimental methods based on current measurement or product quantification are often unable to discern between the contributions from the photocatalytic process and the detrimental effect of the short-circuiting reactions. Here we report on a general electrochemical model of the reaction-diffusion processes to identify and quantify the "bottlenecks" present in the fuel or current generation. The model is able to predict photocurrent-time curves including deconvolution of the recombination contributions, and to visualize the corresponding time dependent concentration profiles of the product. Dimensionless groups are developed for straightforward identification of the limiting processes. The importance of the model for quantitative understanding of biophotoelectrochemical processes is highlighted with an example of simulation results predicting the effect of the diffusion coefficient of the charge carrier on photocurrent generation for different charge recombination kinetics.

The heterogeneous electrolyte of CuFeO2 nano-flakes composited with flower-shaped ZnO for advanced solid oxide fuel cells

The flower-shaped ZnO was synthesized to form composite with the delafossite structure CuFeO2. The composite heterojunction formed for the ZnO-CuFeO2 composite material demonstrates a profound significance for exploring novel materials in solid oxide fuel cell (SOFC) field. At 550 °C, power outputs of 300 mW cm−2 and 468 mW cm−2 were achieved for SOFC devices using pure ZnO and composite with CuFeO2 as the electrolytes, respectively. The composite showed a good performance at low temperatures, for instance, it showed a power output of 148 mW cm−2 at 430 °C. The studies on photocurrent-time curves with visible light on/off irradiation provided an evidence for electron-hole separation. The heterojunctions separate holes and electrons, preventing short-circuiting while used in the SOFC device. These results demonstrate that introducing the heterojunctions in the electrolyte is an innovative approach for advanced SOFCs.

The study of the CdS film and the carrier transport characteristics of CdS/CuInS2 pn junction

Cadmium sulfide (CdS) films were grown by chemical-bath deposition (CBD). Some films were annealed at 300 °C in N2 atmosphere for 30 min. The diffraction peaks related to the (111) crystal plane of wurtzite CdS phase appeared in as prepared CdS films. After annealing, the diffraction peaks related to (220) and (311) crystal planes of wurtzite CdS phase came out. Meanwhile, the roughness, the crystallite sizes and the Cd/S ratio of annealed CdS films increased, which might be due to the volatilization of S element. Furthermore, the absolute values of photocurrent of different CdS films may be related to the interaction between the electron and the intrinsic defects in CdS film and the absorption capacity for incident light. Moreover, the I-V characteristics for all FTO/CdS/CuInS2/Mo hetero-junctions exhibited successful rectifying characteristic, and the corresponding electrical parameters may be attributed to the thickness of CdS films and the intrinsic defects in p-n junction. The figure is the photocurrent-time curves of CdS thin films prepared by different time.

Visible-light-driven selective oxidation of alcohols using a dye-sensitized TiO2-polyoxometalate catalyst

This study demonstrated a dye-sensitized TiO2-polyoxometalate system (denoted TiO2-(PW12-TH)8, where PW12=PW12O403− and TH=thionine) for selective oxidation of alcohols under visible light. The results showed that various substituted alcohols were transformed into their corresponding aldehydes with high selectivity. Due to more efficient electrons transfer, large surface area, and enhanced visible light absorption, the photocatalytic activity of TiO2-(PW12-TH)8 was superior to any other dye-sensitized system reported to date. The response in the photocurrent-time curves over several on/off cycles of intermittent irradiation showed good reproducibility. The photocurrent response of TiO2-(PW12-TH)8 was much higher than that of TiO2/TH (physical mixture of TiO2 and TH), SiO2-(PW12-TH)8 or P25-(PW12-TH)8 (P25=Degussa P25), attributed to the more efficient transfer and longer lifetime of photoexcited electrons. This photocatalytic process confirmed that efficient electron transfer during photocatalytic oxidation plays a vital role in determining the reaction conversion and obtaining good selectivity. Electron paramagnetic resonance (EPR) spectra and radical scavenging experiments proved that superoxide radicals and electrons were the main reactive species in the proposed system, the absence of hydroxyl radicals and holes is demonstrated to be the key of high reaction selectivity.

Enhanced visible light activity on direct contact Z-scheme g-C3N4-TiO2 photocatalyst

Direct contact Z-scheme g-C3N4-TiO2 nanocomposites without an electron mediator are prepared via simple annealing the mixture of bulk g-C3N4 and nanotube titanic acid (NTA) in air at 600°C for 2h. In the process of annealing, the bulk g-C3N4 transformed to ultra-thin g-C3N4 nanosheets, and NTA converted to a novel anatase TiO2, then the two components formed a close interaction. The XPS result reveals that some amount of nitrogen is doped into this novel-TiO2, and g-C3N4 nanosheets exist in the composites. The results of XRD, TEM and TG indicate that the thickness of g-C3N4 nanosheets is very thin. The ESR spectrum shows the existence of Ti3+ and single-electron-trapped oxygen vacancy in the 30%g-C3N4-TiO2 composites. In photocatalytic activity test, the 30%g-C3N4-TiO2 nanocomposites showed an excellent photo-oxidation activity of propylene under visible light irradiation (λ≥420nm), and the removal efficiency of propylene reached as high as 56.6%, and the activity kept nearly 82% after four consecutive recycles. Photoluminescence (PL) result using terephthalic acid (TA) as a probe molecule indicated that the g-C3N4-TiO2 nanocomposites displayed a Z-sheme photocatalytic reaction system and this should be the main reason for the high photocatalytic activity. A possible photocatalytic mechanism was proposed on the basis of PL result and transient photocurrent-time curves.

Photocatalytic Reduction of CO2to Methane on Pt/TiO2Nanosheet Porous Film

Anatase TiO2nanosheet porous films were prepared by calcination of the orthorhombic titanic acid films at 400°C. They showed an excellent photocatalytic activity for CO2photoreduction to methane, which should be related to their special porous structure and large Brunauer-Emmett-Teller (BET) surface area. In order to further improve the photocatalytic activity, Pt nanoparticles were loaded uniformly with the average size of 3-4 nm on TiO2porous films by the photoreduction method. It was found that the loading of Pt expanded the light absorption ability of the porous film and improved the transformation efficiency of CO2to methane. The conversion yield of CO2to methane on Pt/TiO2film reached 20.51 ppm/h·cm2. The Pt/TiO2nanosheet porous film was characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and ultraviolet-visible light diffuse reflectance spectra (UV-vis DRS). Moreover, the transient photocurrent-time curves showed that the Pt/TiO2nanosheet porous film exhibited higher photocurrent, indicating that the higher separation efficiency of the photogenerated charge carriers was achieved.

A facile strategy to passivate surface states on the undoped hematite photoanode for water splitting

A facile strategy was found to passivate surface states on the undoped hematite photoanode by scanning the photocurrent-time curves in saturated NaCl aqueous electrolyte. Incident photon to current efficiency (IPCE) of the hematite photoanode was increased by a factor of 2.6 (from 5% to 13%) at 365nm and 1.23 VRHE (reversible hydrogen electrode) after this pretreatment. This enhancement was ascribed to the surface states passivation, which diminishes the recombination centers of the photogenerated carriers. The surface states passivation was confirmed by current transients and photoluminescence (PL) spectra.

Application of optically transparent electrodes: Part II. Analytical solution of illumination step chronoamperometry for first-order kinetics with the lambert-beer concentration profile

A theoretical study of transient photocurrent-time curves caused by a step functional illumination through an optically transparent electrode, i.e. “illumination step chronoamperometry” is presented for first-order kinetics of the dark back reaction of photochemically generated species with the Lambert-Beer concentration profile. Characteristics of the present method for the study of photo-redox systems consisting of two redox couples A, B and Y, Z which react according to the following scheme: ▪ Electrode B→A±e are discussed in comparison with those of flash electrolysis. The simple cases, whose differential equations can be solved exactly without the aid of digital simulation, are considered and some of the analytical solutions are compared with the previous results by the digital simulation in Part I for the cases of no dark back reaction. Using lower case letters a, b, y, and z for the concentrations of A, B, Y. and Z, the assumptions made can be written as: (1) thermal reaction of A+Z can be ignored and b ∡ a (i.e. a = a 0) in the dark, (2) intensity of illuminated light is not so strong and b ∡ b ∡ a (i.e. a = a 0) even under the illumination, (3) b ∡ y (i.e. y = y 0) for the first order kinetics, (4) to keep the quantum efficiency for the generation of B constant during illumination, b ∡ z (i.e. z = z 0). The effect of double layer charging effect, which cannot be neglected in the photocurrent transient measurements in a short period comparable to the cell time constant, is also discussed, and observable transient photocurrent-time curves taking the effect into account are derived.

Application of optically transparent electrodes: Part III. A double-illumination-step chronoamperometric study of the kinetics of the dark back reaction of photochemically generated leucothionine with iron(III) in the iron-thionine system

Experimental transient photocurrent-time curves caused by a step-functional illumination through an optically transparent electrode (OTE) are compared with theoretical ones for the iron-thionine system. where not only can photochemically generated leucothionine be oxidized and consequently be monitored electrochemically at the OTE, but it can also be oxidized homogeneously with ferric ion in solution. It is also described how the rate constants of this dark back reaction in solution can be determined by double-illumination-step chronoamperometry. The second order rate constant for the reaction was determined to be 190±30 M −1 s −1 at 15±1°C