The relationship between morphology and performance of donor-acceptor rod-coil block copolymer solar cells

Self-assembled functional rod-coil block copolymers (poly(3-hexylthiophene)-b-poly(n-butyl acrylatestatacrylate perylene)) containing electron donor (poly(3-hexylthiophene)) and acceptor (perylene) moieties were synthesized, characterized, and studied in photovoltaic devices. The block copolymers were synthesized by a combination of the McCullough route yielding monodisperse polythiophene, living radical polymerization and finally "click chemistry''. The self-assembled nanostructure was tuned via time to control the degree of order. As a result, devices with active layers which were completely disordered (molecularly mixed), contain short range order in which the nanodomains were molecularly pure, but were poorly organized, or consisted of cylindrical fibrils with their long axes running parallel to the electrodes were compared. Active layers with well formed but poorly organized nanodomains had the highest photovoltaic efficiencies indicating that molecular scale segregation has a significant effect on device performance. The poor performance of the well defined cylindrical nanostructures is probably a reflection of the poor charge transport properties associated with the misorientation of the long axes parallel to the electrodes.