Induced alignment of a reactive mesogen-based polymer electrolyte for dye-sensitised solar cells

Abstract

Liquid crystalline materials are interesting organic molecules possessing anisotropic behaviour. The materials undergo self-assembly forming highly ordered structures, which from the opto-electronic applications point of view, have a promising future. By controlling the functionality or the mesophase of the liquid crystal materials, it is possible to develop specific device architectures. So far, controlling the morphologies of organic materials for electronic applications has proven to be difficult. Here, we prepared a liquid crystal-based polymer template using a polymer alignment layer and electric field. The resultant morphology is closely related to the fabrication technique which can be further modified to suit particular device applications. The mesophase characteristics and morphologies of these materials are characterised using polarising optical microscopy, atomic force microscopy and scanning electron microscopy. Next, we utilised these polymer electrolytes in dye-sensitised solar cells as a potential application. Device performance such as open-circuit voltage, short-circuit current, fill-factor and power conversion efficiencies also showed strong dependence on the structure of the polymer scaffold. Hierarchical polymer electrolyte structures were prepared using a reactive mesogen assisted by Smectic A liquid crystals. The morphology of these hierarchical structures was controlled by the use of alignment layers on the substrate or by applying electric fields. The highest power conversion efficiency achieved was 5.02% in cells with electric field induced alignment, as compared to 4.57% for the polyimide aligned sample. This can be attributed to the higher porosity in the case of the electric field aligned sample whereas for the polyimide aligned sample, despite having more ordered pores, the width between the pores is comparatively smaller.