Hanne Damm

Relation between synthesis conditions, dopant position and charge carriers in aluminium-doped ZnO nanoparticles

The ability to achieve an understanding of the correlations between chemical synthesis, doping mechanism and properties of aluminium-doped zinc oxide (ZnO:Al) nanocrystals is of great importance to evaluate the potential of ZnO:Al nanocrystals as optimal building blocks for solution deposited transparent conductive oxide layers. Two series of Al-doped ZnO nanoparticles were synthesized by solution-based methods under different conditions yielding phase-pure wurtzite ZnO:Al nanocrystals with different morphologies (quasispheres and rods). In both series 80% of the input Al is incorporated in the ZnO:Al crystals. Furthermore, 27Al nuclear magnetic resonance demonstrated a 5 times higher tetrahedral Al content for the quasispheres, which can be directly linked to the presence of free charge carriers, as showed with Fourier transform infrared spectroscopy. XPS data show the Zn2+ and O2− chemical state of the constituting ions. It is demonstrated that an efficient Al doping, creating charge carriers in the ZnO, can be achieved by controlling the chemical synthesis parameters of the nanoparticles.

Combustion deposition of MoO3 films: from fundamentals to OPV applications

A systematic study of a combustion precursors thermal decomposition pathway is undertaken, in both powders and thin films, to obtain insights in the various parameters influencing the combustion process. The study focuses on MoO3 as a hole transporting layer (HTL) for applications in organic photovoltaics (OPV). Via evolved gas analysis, it was found that fuel volatility occurs prior to the actual combustion reaction of the acetylacetonate based precursor, affecting the optimal oxidizer to fuel ratio. Moreover, close investigation showed that the high rate combustion reaction disappears with increasing surface to volume ratio. Nonetheless, thermal analysis performed on films suggests that with the right heating rate, an oxidative complete decomposition still occurs in films, exemplified by the film composition and specific morphological differences in the resulting layers and through analysis of the evolved components. Finally, the discussed synthesis route allows organic free, crystalline MoO3 films to be obtained affording organic solar cell devices with promising current density–voltage characteristics.

Thermal decomposition synthesis of Al-doped ZnO nanoparticles: an in-depth study

Al-doped ZnO nanoparticles are synthesized by means of a heating up solution based thermal decomposition method. The synthesis involves a reaction of zinc acetylacetonate hydrate, aluminium acetylacetonate and 1,2-hexadecanediol in the presence of oleic acid and oleyl amine. A proposed reaction mechanism from reagents to monomers is corroborated by analysis of the evolving gases using headspace GC-MS analysis. The Al-doped ZnO nanoparticles synthesized are dynamically stabilized by adsorbed oleate ions, after deprotonation of oleic acid by oleyl amine, as was found by NOESY proton NMR and complementary FTIR spectroscopy. Precession electron diffraction shows a simultaneous increase in lattice parameters with Al concentration. This, together with HAADF-STEM and EDX maps, indicates the incorporation of Al into the ZnO nanoparticles. By the combination of complementary characterization methods during all stages of the synthesis, it is concluded that Al is incorporated into the ZnO wurtzite lattice as a dopant.

Annealing of sulfide stabilized colloidal semiconductor nanocrystals

The effect of thermal annealing on layers of CuInS2 nanocrystals (NCs) stabilized with (NH4)2S was investigated using in situ transmission electron microscopy (TEM), in situ X-ray diffraction (XRD), thermogravimetric analysis combined with mass spectrometry (TGA-MS) and X-ray photoelectron spectroscopy (XPS). It is shown that these inorganic, chalcogen containing ligands inhibit NC sintering up to 450 °C in an inert atmosphere. On the other hand, sintering can be promoted by annealing in hydrogen gas. A similar behavior is found with Cu2ZnSnSe4 and CdSe NCs. We attribute the inhibited sintering to the oxidation of the S2− originally stabilizing the NCs to sulfite or sulfate moieties, where oxidation is possible either by exposure of the films to air or by thermal decomposition of residual solvent molecules present in the film under inert conditions.