Conductivity enhancement of ZnO:F thin films by the deposition of SnO2:F over layers for optoelectronic applications

Highlights: ► This is the first report on FTO/FZO bilayer. ► A simplified spray pyrolysis technique is employed for the fabrication of the bilayer. ► Quality factor obtained is the highest achieved value so far for ZnO involved bilayer. ► Interesting and desirable electrical results are achieved. ► Structural and electrical results are supplemented by PL studies. - Abstract: Fluorine doped tin oxide (SnO2:F – FTO) layer is deposited over fluorine doped zinc oxide layer (ZnO:F – FZO) so as to get FTO/FZO bilayers with varying thickness proportions of the two layers using a simplified spray pyrolysis technique. In order to analyse the possible enhancement in the transparent conducting properties of these bilayered films, two separate sets of single layered FTO and FZO films are prepared with similar thickness values and their electrical, optical, photoluminescence and structural characteristics are compared with their bilayered counterparts. The electrical studies revealed that the double-layered films with the lesser thickness of FTO exhibit higher sheet resistance (Rsh) and the Rsh value decreases with the increase in the thickness of FTO over layer. The FTO/FZO bilayer with thickness proportions of FTO:FZO nearly equal to 450 nm:300 nm (3:2) is found to have good figure of merit (quality factor) when compared with FZO films. Even though the optical transmittance (T) in the visible range of FTO/FZO bilayer is lesser (80%) than that of FZO (90%) and FTO (85%) films, the electro-optical properties are reasonably good for the bilayered films making them suitable candidates for opto-electronic applications. The photoluminescence studies support the results obtained in the electrical and structural studies.