Main-chain chiral poly(2-oxazoline)s:Influence of alkyl side-chain on secondary structure formation in the solid state

\u3cp\u3eThe influence of the side-chains of main-chain chiral poly(2-oxazoline) s on their thermal properties was investigated using differential scanning calorimetry (DSC) and the nature of the obtained melting endotherms was further investigated by thermal annealing of the polymers. Poly(R-2-ethyl-4-ethyl-2-oxazoline) (p-R-EtEtOx) was found to be amorphous, while polymers with longer side-chains are semicrystalline. Previously we reported that the chirally ordered crystals of poly(R-2-butyl-4-ethyl-2-oxazoline) (p-R-BuEtOx) have a high melting temperature of more than 200°C. in this work we demonstrate that elongation of the side-chains frombutyl to octyl results in a decrease in the crystallization rate and melting temperature suggesting that the chirally ordered crystals of p-R-BuEtOx are based on close packing of the mainchain enhancing diploar interactions between the tertiary amide moieties. Crystallizaiton of chiral polymers with longer side-chains resultsmay then be driven by close packing of the side-chains. This is supported by the observation that further elongation of the sidechain length increases the crystallization rate. Moerover, an additional melting endothermappears for thesepolymers at a lower temperature upon annealing ascribed to a dual crystal size population. Circular dichroism (CD) measurements of the semicrystalline main-chain chiral polymer films revealed the presence of chirally ordered crystals while X-ray diffraction (XRD) patterns revealed a closer packing of the chiral poly(2-alkyl-2-oxazoline) s compared to the non-chiral polymers, suggested to result form the chiral ordering in the crystals. Grazing incidence wide angle x-ray scattering (GIWAXS) patterns indicated that the chiral crystals of p-R-BuEtOx do not form a helical structure, however, the substrate does influence the type of structure formed.\u3c/p\u3

Morphology analysis of near IR sensitized polymer/fullerene organic solar cells by implementing low bandgap heteroanalogue C-/Si-PCPDTBT

In the current work, we have investigated the morphological aspects of the ternary solar cells based on host matrices of P3HT:PCBM and P3HT:ICBA, using the low bandgap polymer analogues of C- and Si-bridged PCPDTBT as near IR sensitizers, which show noticeably different performance. A direct comparison of these well-functional and poorly functional ternary blend systems provides insights into the bottlenecks of device performance and enables us to set up an initial set of design rules for ternary organic solar cells. Our study reveals the importance of surface energy as a driving force controlling sensitizer location and morphology formation of ternary blends. The interfacial surface energy results indicate that Si-PCPDTBT locates at amorphous interfaces and P3HT crystallites, while C-PCPDTBT tends to accumulate at amorphous interfaces and semi-crystalline (or agglomerated) domains of the fullerene derivatives. GIWAXS and SCLC results support this prediction where adding high content of C-PCPDTBT influences mainly the semi-crystallinity (aggregation) of the fullerene and reduces the electron mobility, but Si-PCPDTBT impacts mainly the P3HT ordering and, in turn, deteriorates the hole mobility. These findings show that the disruption of the fullerene semi-crystalline domains is more detrimental to the device performance than the disruption of the polymer domains