Densification of Doped Zinc Oxide Nanocrystal Films via Chemical Bath Infiltration

Colloidal nanocrystals (NCs) hold great promise for the fabrication of thin film devices due to the ability to precisely control their properties and deposit coatings via solution-based protocols. The role of interfaces, surface defects, and (electrical) connectivity between NCs is a major bottleneck to achieving the desired performance. Here, a novel method to infiltrate and densify nanocrystalline coatings deposited from doped ZnO Ncs is presented. Reduced porosity, enhanced connectivity, and a reduction in surface defects are observed, culminating in vastly improved electrical conductivity. Doped ZnO NCs are processed into an ink and used for thin film deposition. Bulky native ligands are then removed from the film to promote better electrical contact between neighboring NCs and render their surfaces hydrophilic. Afterward, a modified chemical bath deposition (CBD) is adopted to slowly infill the pores between the NCs with pure ZnO via a controlled heterogeneous nucleation process. The optimized CBD avoids excessive surface growth and premature sealing of the film surface, confirmed by combined spectroscopic and morphological characterizations. The resultant hybrid films demonstrate enhanced electrical properties, with conductivity increasing by two orders of magnitude after pore infiltration. These results pave the way to hybrid functional coatings with enriched interparticle communication.