Formation of liquid cone jet dependent on rise time of driving voltage

Zero-Dimensional Cs2TeI6 Perovskite: Solution-Processed Thick Films with High X-ray Sensitivity

“…38,42,43 The polarity (permittivity) and conductivity of the precursor solution are critical parameters to determine the spray droplet size under high static electrical field. 37,42,44 The Cs 2 TeI 6 crystals formed immediately as the solvent evaporated from the heated substrate. Figure 2 presents a set of SEM images of the surface of the Cs 2 TeI 6 thick films prepared using a mixed DMF/ethanol solution.…”

“…The Cs 2 TeI 6 solution was spray-coated onto the substrates using a programmable fluid pump. Well-dispersed droplets formed by the Coulomb repulsive force and guided by the electrical gradient between the nozzle and the substrate were densely deposited without any rebound effect. ,, The polarity (permittivity) and conductivity of the precursor solution are critical parameters to determine the spray droplet size under high static electrical field. ,, The Cs 2 TeI 6 crystals formed immediately as the solvent evaporated from the heated substrate. Figure presents a set of SEM images of the surface of the Cs 2 TeI 6 thick films prepared using a mixed DMF/ethanol solution.…”

“…Another crucial parameter is the size of the Cs 2 TeI 6 precursor droplets generated at the nozzle and their dispersion over the substrate during film formation. This is affected by the spray rate, the electrical potential applied on the nozzle, and the distance between the nozzle and the FTO substrate. , Therefore, a well-adjusted balance between solvent evaporation and Cs 2 TeI 6 crystallization rates is necessary. We found that an applied bias of 15 kV coupled to an optimized nozzle-to-substrate distance of 7.5 cm and a solution flow rate of 1.2 mL·h –1 gave sufficiently small spray droplets and a granular surface morphology (Figure e).…”

Precise Morphology Control and Continuous Fabrication of Perovskite Solar Cells Using Droplet-Controllable Electrospray Coating System

“…Contrary to the conventional electrospray systems, we have optimized the inner diameter of the nozzle to solve issues of instability and uncontrollability of electrospray that arise from high conductivity of perovskite solutions. The formation of a stable cone jet in electrospray system is determined by the balance between two characteristic times: the dielectric relaxation time (τ e ), which indicates the response time of the fluid when voltage is applied, and the characteristic time of Taylor cone formation (τ h ). , #tab; where ε is the relative permittivity, K is the electrical conductivity, η is the viscosity, γ is the surface tension of the solvent, ε 0 is the permittivity of free space, and R is the inner radius of the nozzle. When electrical potential is applied, if the τ e is much shorter than the τ h , the fluid tends to be ejected before the Taylor cone is formed on the nozzle tip, which consequently induces unstable and uncontrollable electrospray.…”

“…When electrical potential is applied, if the τ e is much shorter than the τ h , the fluid tends to be ejected before the Taylor cone is formed on the nozzle tip, which consequently induces unstable and uncontrollable electrospray. Therefore, for high conductivity fluids such as perovskite precursor solution, τ h should be shortened by reducing the inner diameter of the nozzle to form a stable Taylor cone. , Thus, we have used a microsized silica nozzle with the inner diameter of 15 μm (Nano NC, Korea) which is not commonly used in the conventional methods. The nozzle is connected to a metal holder to which high voltage is applied by a DC high-power supplier (Nano NC, Korea).…”