Structure–properties of small donor–acceptor molecules for homojunction single-material organic solar cells

Abstract

Homojunction single-material organic solar cells (HOSCs) based on small donor–acceptor molecules represent the ultimate stage of simplification of OSCs. While single-material OSCs based on double-cable polymers or fullerene-based dyads have recently emerged on the forefront of research, the literature contains very few examples of homojunction SMOSCs. In this work a series of small donor–acceptor molecules involving arylamine donor blocks connected to an electron acceptor group by a thienyl or phenyl conjugating bridge has been synthesized. Results of UV-Vis absorption spectroscopy, cyclic voltammetry and theoretical calculations show that the band gap of the materials can be tuned over a wide range by modification of the bridge and acceptor group. The photovoltaic properties of the materials have been evaluated on direct and inverted cells. The two series of devices give consistent results showing that the photocurrent, conversion efficiency and spectral response of the cells are tightly correlated to the chemical structure of the active material. These results thus represent a first step towards a systematic analysis of structure–properties relationships of small D–A molecules as active material for homojunction SMOSCs.