The development of advanced materials with tunable electrical and electronic properties, particularly transparent conducting oxides (TCOs), has been a primary focus in scientific and technological research, as oxides provide superior stability with respect to many other materials. In particular, when selecting materials containing elements that are non-critical. The conductivity of TCO based nanocrystal films remains on the lower side of commercially available inks. In fact in our comparison study we reveal that the resistivity of silver nanowire films usually falls between 10 to 100 µΩ·cm, depending on factors like the density of the nanowires, film thickness, and processing conditions. Copper (Cu) nanoparticle printed films are an emerging alternative to silver and other conductive materials, especially in flexible electronics. he resistivity of copper nanoparticle films typically ranges from 30 to 100 µΩ·cm. Copper films can be more susceptible to oxidation compared to silver, which can increase resistivity over time if not properly protected. While copper nanoparticle films can achieve respectable conductivity, their resistivity is generally higher than that of silver nanoparticle films but can still be competitive. In our study we focussed our attention on indium tin oxide (ITO) nanocrystals (NCs) as a valid alternative to Cu and silver. ITO nanoparticle printed films offer typically low to moderate resistivity, which can be optimized through careful control of composition, thickness, and post-processing, making them highly suitable for transparent conductive applications. Core-shell nanostructures have emerged as a promising platform due to their versatility in modifying intrinsic properties and creating novel functionalities. In that case, a base metal oxide nanocrystal (MO NCs) is produced, serving as the core, and its corresponding core-shell nanostructure is fabricated. In our case, we selected the base material, ITO nanocrystals, with well-defined optical and electronic properties, including a tunable localized surface plasmon resonance (LSPR) in the near-infrared region, a bandgap in the ultraviolet range, and high conductivity. By encapsulating these ITO nanocrystals (core) with an external shell of Indium Oxide (In3O2) ITO/In2O3 core/shell NCs are produced, which significantly modify their intrinsic properties. The core-shell interface introduces novel physical and chemical phenomena that we target to optimize. We tested the hypothesis that shell formation has an influence on the conductivity and upon precise dopant placement the conductivity can be optimized whilst keeping lower the doping density.
Towards this aim, we first targeted the large-scale synthesis of both materials, optimizing synthesis processes to ensure reproducibility and product quality. Subsequently, thin films were fabricated using spin coating, exploring various deposition conditions to obtain films with optimal properties. The films were characterized using electrical conductivity techniques to evaluate the impact of the core-shell structure on device performance, as well as post processing treatments. The device fabricated in this study is a thin-film electrode. The combination of high conductivity and structural stability achieved through the optimized synthesis and fabrication processes makes these thin films suitable for applications in optoelectronic devices. The core-shell structure, particularly the ITO/In2O₃ films, is critical for improving the charge transport and distribution within the films. The results obtained in this study provide deeper insights into the relationship between nanoscale structure and macroscopic properties of these materials, as well as identifying potential applications in flexible electronics, optoelectronics, and energy-related fields. Taken together, the conductivity measurements provided valuable insights into the electrical properties of ITO and ITO/In2O3 thin films, indicating that both the quality of the films and their conductivity improve more significantly with higher annealing temperatures and the use of octane compared to hexane. The superior performance of octane may be attributed to its ability to produce better film quality, potentially due to the differences in solvent interactions and evaporation dynamics, which lead to improved nanoparticle dispersion and a more uniform film morphology. Additionally, the research underscores the advantages of core-shell materials in enhancing conductivity. The interface in core-shell structures plays a critical role in optimizing transport properties, while the core materials exhibit more uniform electrical behavior. These findings highlight the importance of understanding charge transport at interfaces to design materials with improved electrical characteristics.
