p-Type aliovalent Li(I) or Fe(III)-doped CuO hollow spheres self-organized by cationic complex ink printing: Structural and gas sensing characteristics

[Display omitted] •Li(I) or Fe(III)-doped CuO hollow sphere films are prepared via cationic complex ink.•Substitutional doping of aliovalent cations modifies the electronic structure of CuO.•The gas response of CuO toward ethanol was enhanced with aliovalent Fe(III) doping. The p-type CuO hollow sphere films doped with aliovalent Li(I) or Fe(III) have been prepared directly on the substrate through a self-organization process in the printed films using the formulated cationic complex inks. The Li(I) or Fe(III) ions are substitutionally incorporated into CuO lattice with the variation in lattice parameters and act as a shallow acceptor or donor leading to the increase or decrease of the hole density, respectively. Such an electronic modification shifts the optical band gap and binding energy of Cu. The increased hole density by Li(I) doping reduces the overall sensor resistance and the width of hole-accumulation layer (λd) in CuO grains, resulting in the decrease in gas response toward the reducing ethanol gas to ca. 50% compared to that of undoped CuO. In contrast, the decreased hole density by Fe(III) doping increases the sensor resistance and λd, leading to the enhancement in gas response to ca. 150%, based on the electronic sensitization mechanism. These results show clearly that the substitutional doping of aliovalent cation is effective for the manipulation of electronic structure and gas sensing properties of p-type CuO.