In this paper, indium-doped zinc oxide (IZO) films were grown by spray pyrolysis, using zinc acetate and indium acetylacetonate precursors. The focus was on developing a solution recipe based on water as solvent, with only minor acetic acid content, as well as keeping the substrate temperature as low as possible-at 360°C. The process is therefore environment friendly and energy efficient. Despite the challenging conditions, the resulting IZO films were highly transparent and conductive. Their texture deviates strongly from the (002) texture of ZnO and depends on the indium content, which also influences the resistivity. The latter attains its minimum for an indium concentration of 4 at.% in the solution and decreases for increasing film thickness, reaching the value of (5.0 ± 0.1) 9 10 -3 X cm, mainly due to the increase in carrier mobility. The stability of the resistivity after high dose of UV irradiation was found to increase with the carrier density and the film thickness. Thick, highly doped films show minimal resistivity modification even after a total dose of 12.1 kJ/cm 2 UVA/ UVB irradiation. Finally, to demonstrate its applicability in devices, the IZO electrode was used for the fabrication of a lead-perovskite absorber solar cell, yielding an energy conversion efficiency of 6% and 910 mV open-circuit voltage.

A comparative study is presented on chemical bath-deposited ZnO films, doped with the group-13 metals Al, Ga and In. The study reveals marked differences in dopant incorporation in the films, which increases in the order: In, Al and Ga. The presence of dopant in the solution induces significant modifications in the deposition rate, which varies between 110 and 40 nm min -1 . All films are (002)-textured, whereas the lattice stress evolution with the dopant type and concentration suggests that Ga has the highest degree of substitutional incorporation in Zn sites. The average visible transmittance is higher than 80%, while the infrared reflectivity depends on the free carrier density in the films, which is the lowest for undoped ZnO and increases in the order: In-, Al-and Ga-doped ZnO. Optical measurements also yield an inverse correlation between carrier density and mobility. Doping enlarges the bandgap, as well as the Urbach energy that is related to the films' disorder. The lowest electrical resistivity, measured by fourpoint probe, is 1.7 9 10 -2 X cm and is obtained for In-doped films after being exposed to ultraviolet light. Ga-doped films are found to exhibit the highest stability of the conductivity upon ultraviolet exposure.

The paper reports on all-solution-processed, all-oxide solar cells, based on an electrodeposited Cu 2 O absorber. The transparent indium-doped zinc oxide (IZO) contact and buffer layers of zinc oxide or zinc magnesium oxide (Zn 1-x Mg x O) were fabricated by ultrasonic spray pyrolysis. The cells were completed with graphite paste top contacts. The focus was set on using exclusively environment-friendly and low-cost raw materials, deposited from aqueous solutions without organic solvents. The latter is especially important for spray pyrolysis, where high process temperatures restrict the use of flammable solvents. The developed spray pyrolysis recipes yielded conductive (25 X/sq.) and transparent IZO and various compositions of transparent Zn 1-x Mg x O layers, with a linear dependence of the energy band gap (3.28-3.50 eV) as a function of the Mg content (0-16 mol %), as seen for layers deposited by vacuum-based techniques. Solar cells with a Zn 0.88 Mg 0.12 O buffer showed an improved photovoltaic performance compared to cells with ZnO buffer or without buffer, reaching a power conversion efficiency of 0.67% with a short-circuit current density of 3.76 mA/cm 2 , an open-circuit voltage of 0.34 V and a fill factor of 52.7%. The study correlated the improved cell performance with structural and electronic properties of the heterojunction.

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A simple, low-temperature route for the chemical bath deposition of Mg-doped ZnO films, based on low-cost, abundant and non-toxic materials was developed. The film growth mechanism, the resulting morphology and texture were investigated in detail by scanning electron microscopy and X-ray diffraction measurements. It was found that substantial film growth is only possible in a narrow solution pH window due to the Zn(OH) 2 supersaturation as driving force for the film deposition. Different amounts of Mg in the solution cause distinct (0001), (10 10) or (10 11) ZnO crystal textures. Speciation modelling helped to understand the solution chemistry and explain the occurrence of different textures by face-selective adsorption of Mg species onto specific ZnO faces. The amount of incorporated Mg into the ZnO lattice, determined by inductively coupled plasma atomic emission spectroscopy, was limited to 2.1 mol%. Optical band gaps, calculated from transmittance spectra, showed an increase with higher amounts of incorporated Mg and ranged between 3.41 and 3.55 eV.

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