Evaluation of the Dispersion Stability of AZO Mesocrystals for Their Processing into Functional Thin Films Using Small Angle X-ray Scattering

Julian Ungerer,Georg Garnweitner,Ann-Kathrin Thurm,Hermann Nirschl

doi:10.3390/cryst10050374

Abstract

Within the scope of the comprehensive elucidation of the entire process chain for the production of highly functional thin films made of semiconducting aluminum-doped zinc oxide ( A Z O ) nanocrystals, this work deals with the detailed investigation of the stabilization sub-process, considering the requirements for the subsequent coating process. An innovative investigation procedure using non-invasive small angle X-ray scattering ( S A X S ) is developed, enabling an evaluation of qualitative and quantitative dispersion stability criteria of sterically stabilized A Z O nanocrystals. On the one hand, qualitative criteria for minimizing layer inhomogeneities due to sedimentation as well as aggregate formation are discussed, enabling a high particle occupancy density. On the other hand, a procedure for determining the A Z O concentration using S A X S , both in the stable phase and in the non-stabilized phase, is demonstrated to provide a quantitative evaluation of the stabilization success, having a significant impact on the final layer thickness. The obtained insights offer a versatile tool for the precise stabilization process control based on synthesis process using S A X S to meet coating specific requirements and thus a successful integration into the entire process chain for the production of functional A Z O thin films.

Highlights

The field of printable electronics is gaining increasing economic importance and offers the possibility of producing flexible andtransparent electronic components for use in complex systems [1,2,3,4,5]
The production of particulate thin films consisting of transparent conductive oxides (TCOs), which can be applied in displays, organic light-emitting diodes, or thin-film solar cells [6,7,8,9,10], poses a major challenge, since nanoparticular layers often have very low conductivity due to their high interfacial resistances
The particle structure and the fractal properties of aluminum doped zinc oxide (AZO) nanocrystals in an ethanol-based dispersion after synthesis, particle preparation, and before stabilization are examined in more detail using small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and dynamic light scattering (DLS)

Summary

Introduction

The field of printable electronics is gaining increasing economic importance and offers the possibility of producing flexible and (semi-)transparent electronic components for use in complex systems [1,2,3,4,5]. Crystals 2020, 10, 374 particle-based properties for the entire process chain within the fabrication process, starting with the synthesis of the AZO nanocrystals followed by their conversion into stable dispersions up to the coating and drying or post-processing of the final layers. For this purpose, small-angle X-ray scattering (SAXS) as a non-invasive measuring method basically offers the possibility of recording and correlating structural properties in each individual process step independently of the state of the nanoparticles (e.g., powder, dispersion, or thin film) [13,14,15]. In the course of our own previous work, the synthesis of AZO nanocrystals via the benzylamine route could be comprehensively clarified using X-ray scattering analysis methods, on the one hand, by developing a growth model covering the time-resolved growth to hexagonal-shaped mesocrystalline nanoparticles [16] and, on the other hand, by investigating influences of important process parameters on the growth behavior at low reaction kinetics [17]

Methods

Results

Conclusion