Polyol synthesized aluminum doped zinc oxide nanoparticles - influence of the hydration ratio on crystal growth, dopant incorporation and electrical properties

Abstract

The wet chemical deposition of solution processed transparent conducting oxides (TCO) provides an alternative low cost and economical deposition technique to realize large-areas of conducting films. Since the price for the most common TCO Indium Tin Oxide rises enormously, Aluminum Zinc Oxide (AZO) as alternative TCO reaches more and more interest. The optoelectronical properties of nanoparticle coatings strongly depend beneath the porosity of the coating on the shape and size of the used particles. By using bigger or rod-shaped particles it is possible to minimize the amount of grain boundaries resulting in an improvement of the electrical properties, whereas particles bigger than 100 nm should not be used if highly transparent coatings are necessary as these big particles scatter the visible light and lower the transmittance of the coatings. In this work we present a simple method to synthesize AZO particles with different shape and size, but comparable electronical properties. We use a simple, well reproducible polyol method for synthesis and influence the shape and size of the particles by adding different amounts of water to the precursor solution. We can show that the addition of aluminum as dopant strongly hinders the crystal growth but the addition of water counteracts this, so that both, spherical and rod-shaped particles can be obtained.

Characterization and Optimization of AZO Nanoparticles as Coatings for Flexible Substrates toward High IR Reflectivity

“…Both lead to a slight increase of crystallite sizes for the [100] and [101] planes. Similar to our previously reported observation on the effect of hydration, the preferred growth direction is [002] . The crystallite size increases as a function of the precursor concentration, and the measurements indicate a uniform growth in all directions at concentrations between 0.063 and 0.25 mol/L (Figure c).…”

“…For the coating of flexible and heat-sensitive substrates like technical textiles and roofing membranes commonly used in architecture, TCO particles can be synthesized and deposited on the substrate by wet-chemical applications in a two-stage process. Such coatings can be applied with common techniques under mild conditions. , …”

“…Doping ZnO with aluminum generates highly conductive particles (aluminum-doped zinc oxide, AZO) with Al being an inexpensive substituent for a chemically and thermally stable product. ,, Al 3+ ions can substitute for or co-locate with different zinc and oxygen ions in the wurtzite structure. As at least four different lattice sites are discussed that could be occupied by the dopants, the doping mechanisms in a wet-chemical synthesis approach are very complex …”

“…Zinc acetate dihydrate and aluminum nitrate nonahydrate were used as precursors and diethylene glycol with a fixed amount of water as a solvent. Based on our previously published results, the water-to-metal-ion ratio was fixed at 3:1 . Changes in the physical and chemical properties of the AZO particles were observed depending on the reaction temperature and time, the Al doping degree, and the precursor concentration in solution.…”

Ba33Zn22Al8O67 with a Framework of ([O(Zn/Al)4]/Ba)(Zn/AlO4)4 Motifs

“…1-dimensional 27 Al DE-MAS NMR spectrum of Ba 33 Zn 22 Al 8 O 67 (Figure a) reveals two resonance peaks at 79.2 and 84.9 ppm, which are characteristic of Al in four-fold coordination with O (i.e., AlO 4 ). The positions of the peaks (chemical shifts, δ) are similar to those in the spectrum of Al-doped ZnO powder. − In previous studies, the chemical shifts were interpreted as some of the tetrahedral Zn sites being substituted by Al atoms, where the observed Al environment can be described as a Q 4 (4Zn) configuration. In the present study, Q n ( m T) is defined as follows: Q is the tetrahedral Al, n is the degree of condensation, T is a second neighboring tetrahedral atom (Al or Zn), and m is the number of bonding T atoms via oxygen.…”