Dual effect to improve the electrical properties of SZO films grown by nitrogen pneumatic spray pyrolysis

The principal aim of this study is to reduce considerably, via Sn doping, the resistivity of ZnO thin films prepared by simple, flexible, and cost-effective nitrogen pneumatic spray pyrolysis (NPSP) method on glass substrates at a temperature of 400°C. Different Sn content was tested (Sn/Zn = 0, 1, 3, 5 wt%) in an attempt to reduce the concentration of excessive oxygen atoms and create more free electrons. The microstructural, optical, morphological, and electrical properties of the films have been studied. The x-ray diffraction analysis demonstrated that tin-doped SZO films exhibited polycrystalline nature with a preferential orientation along (002) plane with the appearance of a new orientation (101) with the increase of Sn concentration leading then to bidirectional growth. The deposited SZO films showed an average optical transmittance of about 80% in the UV-visible region (200-800 nm) with optical band gap values at around 3.27 eV. Photoluminescence emissions of SZO samples presented three main peaks: near band edge emission, violet emission, and the blue-green emission. The surface morphology of the films obtained by scanning electron microscope (SEM) exhibited the change in morphology with increasing the Sn content. A minimum electrical resistivity value of about 17·10^-3 Ω·cm was obtained for 3% SZO films. SZO films prepared by the NPSP method can be used as transparent window layer and electrodes in solar cells. RESEARCH HIGHLIGHTS: Highly oriented, conducting, and transparent Sn-doped ZnO films are successfully synthesized. The film growth orientation changed from mono-directional (002) axis to bi-directional (002) and (101) axis according to Sn doping. Ultraviolet and green emissions are noted by photoluminescence investigation. A minimum resistivity is observed for 3 wt% SZO film. The dual positive effect of the carrier gas used (N₂) and Sn doping is confirmed.