Sub-10 nm nano-structured carbohydrate-based block copolymer thin films for organic photovoltaic applications

Nanoscale patterning through self-assembly of block copolymers is one of the promising bottom-up strategies for controlling active layer morphology in organic photovoltaics. In this thesis, a new class of carbohydrate-based semiconducting block copolymers consisting of π-conjugated regioregular poly(3-hexylthiophene) (P3HT) and oligosaccharides were synthesized and self-organized into sub-10 nm scale periodic nanostructures. Two different diblock copolymers, i.e. P3HT-block-peracetylated maltoheptaose (P3HT-b-AcMal7) and P3HT-block-maltoheptaose (P3HT-b-Mal7) were synthesized via "click" reaction between end-functionalized oligosaccharide and P3HT moieties. A comprehensive investigation of their self-assembly behavior by AFM, TEM, and X-ray scattering analyses revealed that the P3HT-b-AcMal7 diblock copolymer has the ability to self-assemble into sub-10 nm scale lamellar structure, which is the ideal morphology of the active layer in organic photovoltaics and one of the smallest domain sizes achieved by self-assembly of P3HT-based block copolymers, via thermal annealing. Nano-patterned film made of P3HT was attained by selective chemical etching of AcMal7 block from microphase-separated P3HT-b-AcMal7 template without affecting the original lamellar structure. The resultant void where the etched-out AcMal7 block existed will be filled with electron acceptor compounds such as [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) for photovoltaic application as a perspective of this thesis. The results and knowledge obtained in this study are expected to provide further advances and innovation in organic photovoltaics.