Charge Separation Region Research Articles

Single Source, Surfactant‐Free, and One‐Step Solvothermal Route Synthesized TiO2 Microspheres for Highly Efficient Mesoscopic Perovskite Solar Cells

The instant extraction and transmission of photogenerated charge carriers is the key factor to obtain efficient perovskite solar cells (PSCs). The mesoporous electronic transport layer can provide heterogeneous nucleation sites for high‐quality perovskite films and expand the charge separation region to better balance charge transport. Therefore, compared with planar PSCs, most mesoporous PSCs usually exhibit superior photovoltaic performance. Herein, TiO2 microspheres with high crystallinity and purity are synthesized by a single source, surfactant‐free, and one‐step solvothermal reaction strategy. The morphology character of TiO2 mesoporous layers is conducive to good permeation and interfacial contact of perovskite. The gradient adjustment of energy level by the insertion of TiO2 mesoporous layer in the device is beneficial for the effective extraction of electrons. Finally, the optimized mesoporous PSCs can achieve an efficiency of 20.95% with slight hysteresis and satisfactory reproducibility.

Investigations on the plasma enabled growth of vertical graphene sheets on CNT surface

A theoretical model is developed to describe the plasma-assisted nucleation and growth kinetics of a vertical graphene (VG) sheet on a carbon nanotube (CNT) surface. The present model accounts the formalization of a charge separation region, i.e., plasma sheath between the bulk plasma and substrate surface in one-dimension along with the kinetics of all the plasma species (neutrals, positively charged species, and electrons), rate of charge accumulation on the graphene sheet surface, and growth of the VG sheet on the CNT surface owing to defect generation and various processes on the CNT surface. Using the model, we demonstrated that variations in the plasma enhanced chemical vapor deposition process control parameters such as the total gas pressure, input power, and substrate bias can be used for significant variation in the plasma composition and characteristics that in turn control the ion bombardment and generation of carbon species on the CNT surface and consequently tune the VG sheet growth characteristics such as height, thickness, and number density profiles of the VG sheet on the CNT surface. The results of the present study indicate that as the total gas pressure is lowered and the input power and substrate bias are enhanced, the number densities and height of the VG sheet on the CNT surface are increased; however, the thickness of the VG sheet is reduced. Some of our theoretical findings are in good agreement with the existing experimental results.

Suppressing longitudinal double-layer oscillations by using elliptically polarized laser pulses in the hole-boring radiation pressure acceleration regime

It is shown that well collimated mono-energetic ion beams with a large particle number can be generated in the hole-boring radiation pressure acceleration regime by using an elliptically polarized laser pulse with appropriate theoretically determined laser polarization ratio. Due to the J × B effect, the double-layer charge separation region is imbued with hot electrons that prevent ion pileup, thus suppressing the double-layer oscillations. The proposed mechanism is well confirmed by Particle-in-Cell simulations, and after suppressing the longitudinal double-layer oscillations, the ion beams driven by the elliptically polarized lasers own much better energy spectrum than those by circularly polarized lasers.

Predicting the potential for lightning activity in Mediterranean storms based on the Weather Research and Forecasting (WRF) model dynamic and microphysical fields

A new parameter is introduced: the lightning potential index (LPI), which is a measure of the potential for charge generation and separation that leads to lightning flashes in convective thunderstorms. The LPI is calculated within the charge separation region of clouds between 0°C and −20°C, where the noninductive mechanism involving collisions of ice and graupel particles in the presence of supercooled water is most effective. As shown in several case studies using the Weather Research and Forecasting (WRF) model with explicit microphysics, the LPI is highly correlated with observed lightning. It is suggested that the LPI may be a useful parameter for predicting lightning as well as a tool for improving weather forecasting of convective storms and heavy rainfall.

Virtual Device Simulator of Bipolar Photogalvanic Cell

A virtual bipolar photogalvanic cell was developed using Visual Basic. On the basis of the simulation, it is indicated that the charge separation (kd) and the charge recombination (kr) rate constants can be estimated using the photocurrent response. The thickness of the charge separation region can be anticipated by photocurrent response at various layer thicknesses. The increase in diffusion coefficients raises the short-circuit photocurrent to enhance the performance of the photogalvanic cell. An actual device was fabricated using tris(bipyridine)ruthenium(II) complex ([Ru(bpy)3]) as a sensitizer and Prussian Blue as a mediator. This device worked as a photogalvanic cell: short-circuit photocurrent (JSC), 2.3μA/cm2; open-circuit photovoltage (VOC), 0.118V; fill-factor, 20.5 %. It was shown from the action spectrum that electrons are transferred from [Ru(bpy)3] to Prussian Blue. The charge separation and the recombination rate constants were estimated, using the virtual device, to be 5 102 mol-1cm3s-1 and 6 109 mol-1cm3s-1, respectively.

Velocity measurement of the ablated particles during picosecond laser ablation

The laser-induced plasma plume dynamics for picosecond laser ablation of silicon and YBaCuO targets have been studied using optical time-of-flight spectra. The picosecond pulse ablation allows one to reduce the temperature and velocity dispersion of the ablated species. The expansion velocities of the ionized species show an inverse square root dependence vs. the atomic mass and are proportional to their charge. The velocities of the neutral atoms exhibit a much weaker dependence vs. atomic mass. The formation of a charge separation region was observed during plasma plume expansion. These experimental results support the Coulomb expansion mechanism of the laser-induced plasma.

Analysis of the seeded combustion gas boundary layer near a cold electrode

The boundary layer of potassium-see ded combustion gas over a cold electrode under the condition of diffusive current mode without arcs is studied theoretically and experimentally. The theoretical analysis features the introduction of charge separation between electrons and ions, electron thermal nonequilibrium, finite ionization rate, and no assumption of thin sheath layer adjoining the electrode surface. To simplify the problem, the case when the current is produced by an applied external electric field without a magnetic field is studied. In this paper, because of the reliability and suitability of the electric boundary condition adopted in the analysis, the boundary layer around the anode is specifically taken up. For the laminar boundary layer, numerical results for the colder electrode and smaller seed fraction show that the region of the electron-ion charge separation extends much wider than the Debye length from the surface and that both electron thermal and ionizational nonequilibria are considerably remarkable near the electrode even in the seeded combustion gas, and the calculated performance of the electrode voltage drop and current density agrees fairly well with experimental results. On the other hand, for the turbulent boundary layer under the condition of practical MHD generator operation, it is shown from numerical calculations that the charge separation region is limited to the extent of several Debye lengths from the surface and that the electron number density is very close to that obtained by Saha equation for the electron temperature.

Potential distribution in the charge separation region of a plasma boundary layer

The approximation of a test particle moving in an average force field is used to obtain an equation for the potential in the charge separation region. It is shown that effects associated with the interaction of the charges in the layer can be taken into account by introducing dynamic forces (dynamic friction, deceleration due to charge transfer on the ions, loss of energy of excitation, and so on).

Photoelectrochemical effects in the electrolyte-pigment-metal system

Using a semitransparent metallic electrode covered with a thin film of metal-free phthalocyanine, photoelectrochemical effects have been studied in the electrolyte-pigment-metal system. Measurement of the short-circuit photocurrent, produced by continuous illumination, allows description of a photodependent kinetic phase corresponding to the establishment of a stationary state in the charge separation region of the system after the creation of the current carriers.