Crystallisation behaviour of PCDTBT in thin films

Chapter 1 introduces the reasons behind this study, the importance and applications of PCDTBT in organic electronic devices, thus the importance of understanding how confinement in thin films influences the crystallisation of this polymer which will have an impact on the electronic properties of the material. Chapter 2 describes the analytical techniques used (ellipsometry, atomic force microscopy and grazing incidence X-ray scattering) and their importance for this study. In chapter 3 is reported the thermal protocol that allowed the understanding of the crystallisation of PCDTBT; ellipsometry, GIWAXS and AFM results are reported in order to understand the importance of the protocol and also aid the comprehension of the rest of the thesis. Chapter 4 describes how different annealing temperatures influence the crystallisation kinetics and the amount of crystallinity in a sample. Chapter 5 looks in detail at a phenomenon occurring in the film that was quite unpredicted: the ellipsometry data are used to follow the change of the thickness of the film under the thermal treatment explained in chapter 3; an initial shrinking at the ellipsometry shows the crystallisation phenomenon, but what is causing a second expansion which is following the crystallisation. In chapter 6 is finally reported the influence of the film thickness on the crystallisation properties of the material; the influence of the two interfaces on its ordering is key in understanding how to improve the efficiency of organic electronic devices

Zn(II) and Ni(II) complexes with poly-histidyl peptides derived from a snake venom

The snake venoms are complex mixtures containing many bioactive peptides and proteins; some of them are aimed to protect the snake glands, where the venom is stored, until the latter is inoculated in the victim. In the venom of some vipers of the genus Atheris, a set of peptides containing poly-His and poly-Gly segments was recently found. Poly-His peptides are not rare in Nature. Although their exact biological function is most often unknown, one thing is certain: they have good binding properties towards the transition metal ions. As a matter of fact, the imidazole side chain of histidine is one of the groups most frequently involved in metal complexation in the active sites of metallo-enzymes. This is also true for snake-venom metallo-proteases, which contain Zn(II) and Ca(II) ions.In the present paper, the complex-formation ability of the poly-His-poly-Gly peptide found in the venom of Atheris squamigera (EDDH9GVG10-NH2) towards the Zn(II) and Ni(II) ions was investigated by means of thermodynamic and spectroscopic techniques. Two model peptides, derived from the poly-His portion of this peptide but where His residues were alternated with alanines (Ac-EDDAHAHAHAHAG-NH2, and Ac-EDDHAHAHAHAHG-NH2) were also studied, for the sake of comparison. The high affinity of these peptides for the metal ions under investigation was confirmed. In addition, it was demonstrated that the number of His residues in the peptide and their relative position play a main role in the complex-formation ability of the ligand. The very high affinity of EDDH9GVG10-NH2 for Zn(II) can be the key for its role in the inactivation of the venom in the snake glands

Understanding and controlling morphology evolution via DIO plasticization in PffBT4T-2OD/PC71BM devices

We demonstrate that the inclusion of a small amount of the co-solvent 1,8-diiodooctane in the preparation of a bulk-heterojunction photovoltaic device increases its power conversion efficiency by 20%, through a mechanism of transient plasticisation. We follow the removal of 1,8-diiodooctane directly after spin-coating using ellipsometry and ion beam analysis, while using small angle neutron scattering to characterise the morphological nanostructure evolution of the film. In PffBT4T-2OD/PC71BM devices, the power conversion efficiency increases from 7.2% to above 8.7% as a result of the coarsening of the phase domains. This coarsening process is assisted by thermal annealing and the slow evaporation of 1,8-diiodooctane, which we suggest, acts as a plasticiser to promote molecular mobility. Our results show that 1,8-diiodooctane can be completely removed from the film by a thermal annealing process at temperatures ≤100 °C and that there is an interplay between the evaporation rate of 1,8-diiodooctane and the rate of domain coarsening in the plasticized film which helps elucidate the mechanism by which additives improve device efficiency