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ZnO:In thin films were grown from 100 mL of spray solution on glass substrates by chemical spray atTs=400°C using 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 from2·1019 cm−3to1·1020 cm−3when spray rate is increased from 0.5 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 from 0.5 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.

To reduce the use of toxic and expensive elements in chalcopyrite thin film solar cells, materials such as cadmium or indium used in buffer layers need to be substituted. Zn(O,S) is considered to be a potential buffer layer material when deposited with a fast and inexpensive method. Zn(O,S) layers have been prepared by aerosol assisted chemical vapour deposition (AACVD) technique. AACVD technique is a simple non-vacuum process where the thin film deposition temperatures do not exceed 250°C. 10 mM spray solution was made by dissolving zinc(II)acetylacetonate monohydrate in ethanol. The films were grown on Mo substrate at 225°C (film growth temperature). The effect of deposition parameters (spray solution concentration, N 2 flow rate, H 2 S flow rate) on Zn(O,S) thin film properties were studied with SEM and XRD. Thereupon optimizing the deposition parameters, homogeneous and compact Zn(O,S) thin films were obtained and the films were employed in the chalcopyrite thin film solar cell structure by growing films on Cu(In,Ga)(S,Se) 2 substrates industrially produced by BOSCH Solar CISTech GmbH. The resulting cells were studied using current-voltage and quantum efficiency analysis and compared with solar cell references that include In 2 S 3 and CdS as buffer layer deposited by ion layer gas reaction and chemical bath deposition, respectively. The best output of the solar cell containing Zn(O,S) as buffer layer and without intrinsic ZnO under standard test conditions (AM 1.5G, 100 mW/cm 2 , 25°C) is: Voc=573 mV, Jsc=39.2 mA/cm 2 , FF=68.4% and efficiency of 15.4% being slightly better than the In 2 S 3 or CdS containing solar cell references.

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