A structural study of p-type A-D-A oligothiophenes: Effects of regioregular alkyl sidechains on annealing processes and photovoltaic performances

Abstract

In this study we report on a series of 12 small molecular p-type penta- and hexathiophene semiconductors end-capped with either malononitrile (MN), hexyl rhodanine (HR) or dicyano hexyl rhodanine (CHR) acceptors and functionalized with alkyl sidechains of two different lengths, orientated away from the central core in a regioregular manner. Organic photovoltaic devices were fabricated, and annealed using conditions optimized for each material to produce a wide range of power-conversion efficiencies (PCEs) from 1-8%. We find that achieving high PCEs is critically dependent on matching the conjugation length to specific end-group acceptors, and also find a slight correlation between improved p..