Mixing and Interfacial Composition in Polymer/Fullerene Thin Films

Abstract

Organic photovoltaic (OPV) devices use polymers and small-molecules, such as fullerenes, and offer an alternative to conventional inorganic devices. To achieve commercial success OPV devices require well-controlled morphologies and increased device lifetimes. The film morphology of these devices is complex: both mixing and crystallisation can occur. In this thesis, the fundamental behaviour of two model polymer/fullerene systems is investigated. The impact of parameters such as film thickness, molecular weight (MW) of the polymer and annealing temperature, on crystallisation and mixing are examined.

Interfacial width and phase equilibrium in polymer-fullerene thin-films

“…g A GIXD detector map from a crystallised PCBM single layer annealed at higher temperatures and for longer times than used in the present bilayer study ( measurements on samples that had been annealed for a standard time of 5 min (although equilibration was checked for other Mw samples at various temperatures, by annealing some samples for shorter times). In-situ annealing/neutron reflectivity measurements that were performed on 2-20k PCBM/PS bilayers, also found that the bulk of the PCBM diffusion was concluded within a 5 min period, following a temperature step 58 . Layer thickness could in-principle influence the measured composition profile in the bilayers.…”

“…Fullerenes were dissolved in chlorobenzene and then spincoated onto silicon substrates that had been sonicated in acetone and isopropanol (for 15 min each) and then rinsed in de-ionised water. The PS layers were spincoated from toluene solutions onto freshly cleaved mica substrates, and then floated on top of the silicon/fullerene in a bath of de-ionised water (further details in Mon et al 43 and Hynes 58 ). The samples were then placed under vacuum at room temperature (and in the dark) for at least 2 h. Samples were then stored in the dark, and were annealed within a few days of fabrication.…”

“…1-12, 15, 19-21, Supplementary Notes 1-5 and Supplementary Methods). Further discussion of the data reduction, data analysis and robustness tests can also be found in Hynes 58 .…”

Nucleation Front Proliferation in Bi-modal PCBM Crystals and a Crystal Fan – Axial Morphological Transition.

“…Sample fabrication; Fullerenes were dissolved in chlorobenzene and then spin-coated onto silicon substrates that had been sonicated in acetone and isopropanol (for 15 minutes each) and then rinsed in de-ionised water. The PS layers were spin-coated from toluene solutions onto freshly-cleaved mica substrates, and then oated on top of the silicon/fullerene in a bath of de-ionised water (further details can be found in Môn et al 29 and Hynes 44 ). The samples were then placed under vacuum at room temperature (and in the dark) for at least 2 hours.…”