Erki Kärber

Photoluminescence of spray pyrolysis deposited ZnO nanorods

Photoluminescence of highly structured ZnO layers comprising well-shaped hexagonal rods is presented. The ZnO rods (length 500-1,000 nm, diameter 100-300 nm) were grown in air onto a preheated soda-lime glass (SGL) or ITO/SGL substrate by low-cost chemical spray pyrolysis method using zinc chloride precursor solutions and growth temperatures in the range of 450-550°C. We report the effect of the variation in deposition parameters (substrate type, growth temperature, spray rate, solvent type) on the photoluminescence properties of the spray-deposited ZnO nanorods. A dominant near band edge (NBE) emission is observed at 300 K and at 10 K. High-resolution photoluminescence measurements at 10 K reveal fine structure of the NBE band with the dominant peaks related to the bound exciton transitions. It is found that all studied technological parameters affect the excitonic photoluminescence in ZnO nanorods.PACS: 78.55.Et, 81.15.Rs, 61.46.Km

Effect of solution spray rate on the properties of chemically sprayed ZnO: in thin films

ZnO:In thin filmswere grown from 100 mL of spray solution on glass substrates by chemical spray at Ts = 400°Cusing solution spray rates of 0.5-6.7 mL/min. Zinc acetate and indium(III)chloride were used as Zn and In sources, respectively, with [In]/[Zn] = 3 at.%. Independent of solution spray rate, the crystallites in ZnO:In films grow preferentially in the (101) plane parallel to the substrate. The solution spray rate influences the surface morphology, grain size, film thickness, and electrical and optical properties. According to SEM and AFM studies, sharp-edged pyramidal grains and canvas-resembling surfaces are characteristic of films grown at spray rates of 0.5 and 3.3 mL/min, respectively. To obtain films with comparable film thickness and grain size, more spray solution should be used at low spray rates. The electrical resistivity of sprayed ZnO:In films is controlled by the solution spray rate. The carrier concentration increases from 2ċ1019 cm-3 to 1ċ1020 cm-3 when spray rate is increased from0.5 mL/min to 3.3 mL/min independent of the film thickness; the carrier mobilities are always lower in slowly grown films. Sprayed ZnO:In films transmit 75-80% of the visible light while the increase in solution spray rate from0.5 mL/min to 3.3 mL/min decreases the transmittance in the NIR region and increases the band gap in accordance with the increase in carrier concentration. Lower carrier concentration in slowly sprayed films is likely due to the indium oxidation.

Sb2S3 grown by ultrasonic spray pyrolysis and its application in a hybrid solar cell

Chemical spray pyrolysis (CSP) is a fast wet-chemical deposition method in which an aerosol is guided by carrier gas onto a hot substrate where the decomposition of the precursor chemicals occurs. The aerosol is produced using an ultrasonic oscillator in a bath of precursor solution and guided by compressed air. The use of the ultrasonic CSP resulted in the growth of homogeneous and well-adhered layers that consist of submicron crystals of single-phase Sb2S3 with a bandgap of 1.6 eV if an abundance of sulfur source is present in the precursor solution (SbCl3/SC(NH2)2 = 1:6) sprayed onto the substrate at 250 °C in air. Solar cells with glass-ITO-TiO2-Sb2S3-P3HT-Au structure and an active area of 1 cm2 had an open circuit voltage of 630 mV, short circuit current density of 5 mA/cm2, a fill factor of 42% and a conversion efficiency of 1.3%. Conversion efficiencies up to 1.9% were obtained from solar cells with smaller areas.

Low-cost plasmonic solar cells prepared by chemical spray pyrolysis

Summary Solar cells consisting of an extremely thin In2S3/CuInS2 buffer/absorber layer uniformly covering planar ZnO were prepared entirely by chemical spray pyrolysis. Au nanoparticles (Au-NPs) were formed via thermal decomposition of a gold(III) chloride trihydrate (HAuCl4·3H2O) precursor by spraying 2 mmol/L of the aqueous precursor solution onto a substrate held at 260 °C. Current–voltage scans and external quantum efficiency spectra were used to evaluate the solar cell performance. This work investigates the effect of the location of the Au-NP layer deposition (front side vs rear side) in the solar cell and the effect of varying the volume (2.5–10 mL) of the sprayed Au precursor solution. A 63% increase (from 4.6 to 7.5 mA/cm2) of the short-circuit current density was observed when 2.5 mL of the precursor solution was deposited onto the rear side of the solar cell.

Chlorine Doping of Cadmium Sulfide on the Example of CBD CdS

The role of thermal annealing and of CdCl 2 as a main source of electrically active but vaporizable chlorine doping in chemical bath deposited CdS thin films is studied. The films were deposited on glass substrates from aqueous solution of either CdCl 2, NH 4Cl, NH 4OH, and thiourea, or CdSO 4, (NH 4)2SO 4, NH 4OH, and thiourea. Films deposited in the presence of CdCl 2 and annealed in H 2 atmosphere at 310 and 420 °C show a resistivity lower than 10 � ·cm, one order of magnitude less than for identically annealed films deposited in absence of CdCl 2. Annealing at 420 °C in closed ampoules, where a counter pressure of CdCl 2 builds up, leads to a lower resistivity on the order of 10 -1 � ·cm, confirming the key role of chlorine on the electronic properties. However, further characterization via photoluminescence raises new questions about chlorine-related defects and their role in the mechanisms that govern film resistivity.

Modification of light absorption in thin CuInS2 films by sprayed Au nanoparticles

The chemical spray pyrolysis method was used to deposit CuInS2 (CIS) thin films and Au nanoparticles (NPs) in two configurations: glass/Au-NP layer covered with CuInS2 film (Au-NP/CIS) and glass/CuInS2 films covered with Au-NP layer (CIS/Au-NP). According to X-ray diffraction (XRD), the spray of 2 mM HAuCl4 aqueous solution with a volume of 2.5 to 15 ml onto a glass substrate at 340°C results in metallic Au nanoparticles with a similar mean crystallite size in the range of 30 - 38 nm. The mean crystallite sizes remain in the range of 15 - 20 nm when grown onto a CIS film. The prepared films show plasmonic light absorption with increasing intensity in the spectral range of 500- 800 nm when increasing the volume of HAuCl4 solution sprayed. When compared to bare CIS on glass, the absorptance was increased ca. 4.5 times in the case of glass/Au-NP/CIS and ca. 3 times in the case of glass/CIS/Au-NP configuration. The glass/Au-NP/CIS configuration had an advantage since Au-NP could be embedded without chemically damaging the CIS.

Aqueous photocatalytic degradation of selected micropollutants by Pd-modified titanium dioxide in three photoreactor types

ABSTRACT The goals of the present study were to synthesise highly efficient Pd-TiO2 photocatalyst, to characterise its performance in slurry in smaller scale and to investigate its performance in the aqueous photocatalytic oxidation of three antibiotics: doxycycline, sulphamethizole and amoxicillin. The performance of the photocatalyst was evaluated in an open batch slurry reactor equipped with a fluorescent long-wavelength ultraviolet (UVA) lamp (0.2 L). With the fastest degrading doxycycline, experimental research was continued in a fixed-bed continuous flow photoreactor (0.13 L), with the Pd-TiO2 photocatalyst attached to a glass plate, and a medium laboratory-scale three-phase fluidised-bed reactor (2 L) equipped with four fluorescent UVA lamps, with the photocatalyst attached to the surface of expanded clay granules employed as the bed material. While showing very high activity in the batch slurry reactor, far surpassing P25 Aeroxide, the performance of Pd-TiO2 with doxycycline was comparable to P25 in the semi-continuous reactors. GRAPHICAL ABSTRACT