DOI: https://doi.org/10.29363/nanoge.sus-mhp.2022.032
Publication date: 15th November 2022
SnO2 and NiO are wide bandgap semiconducting metal oxides with applications in a variety of fields, including UV light sensing, gas sensing, and as a transparent conductor for LEDs and solar cells. Thanks to their wide bandgap energy, SnO2 and NiO are almost completely transparent to visible light, and thus ideal for UV detection. Metal oxides have traditionally been fabricated by physical and chemical deposition methods. Nevertheless, solution-processing approaches have gained prominence in the last years because of their versatility and controllability in layer deposition. In particular, technologies such as inkjet printing or spin coating enable controlled deposition of wide range of materials.
Inkjet printing is a digital deposition technique based on controlled ink ejection from a series of nozzles placed in printing head. As the printing head travels above the substrate, the ink is deposited in the form of a matrix of droplets in a specified pattern with high precision without the use of masks or photolithography. Despite these advantages, inkjet-printed layers are prone to surface irregularity. In contrast, with spin coating a thin layer is achieved by spreading a certain amount of solution through high-speed substrate rotation. Even though better surface regularities are achieved through spin coating, it cannot control the deposition pattern.
In this work, we compare the performance of high-quality inkjet-printed and spin-coated SnO2/NiO heterojunctions. Single layers of SnO2 and NiO deposited by both approaches are thoroughly studied by a variety of structural and optical techniques. SEM and profilometry show low surface roughness and a lack of pinholes. Optical absorption and conductivity measurements exhibited layers with good transparency and electrical conductivity. Heterojunctions combining these two metal oxides (ITO/SnO2/NiO/Ag), , were fabricated using both techniques. A large current ratio between negative and positive polarizations was observed together with a notable UV photodetection. Thus, nkjet-printed devices show results comparable to spin coated ones. These promising results showed that our inkjet-printed metal oxides are applicable to detect UV as well as for use as transparent charge conductors for either LEDs or solar cells.