Effects of ZnO buffer layer on characteristics of ZnO:Ga films grown on flexible substrates: Investigation of surface energy, electrical, optical, and structural properties

Ga-doped ZnO (GZO) transparent conductive oxide thin films were deposited on flexible polyethersulphone (PES) substrates by radio-frequency sputtering at room temperature. With the addition of an optimized 100-nm-thick ZnO buffer layer, the transmittance, carrier concentration, Hall mobility, and resistivity of GZO films improved from 88.3 to 94.45%, -2.89 × 10²¹ to -3.39 × 10²¹ cm-³, 1.76 to 7.97 cm²/V-s, and 1.32 × 10^-3 to 2.201 × 10^-4 Ω-cm, respectively. The higher surface energy (49.85 mJ/m²) of the 100-nm-thick ZnO layer deposited on the PES substrate compared to those of a bare PES substrate and ZnO layers of other thicknesses deposited on PES substrates is likely responsible for the superior GZO quality obtained with the GZO/100-nm-thick ZnO buffer/PES structure. Moreover, the best adhesion at the GZO surface was observed for the GZO/100-nm-thick ZnO buffer/PES structure based on it having the highest surface energy (67.33 mJ/m²). The GZO/100-nm-thick ZnO buffer/PES structure thus has potential to replace the GZO/PES structure for use in flexible transparent optoelectronic devices.