A Solution-Processable Small Molecule Based on Benzodithiophene and Diketopyrrolopyrrole for High-Performance Organic Solar Cells

Organic photovoltaic devices and solar cells (OPVs) that can be fabricated by simple solution processing techniques are under intense investigation in academic and industrial laboratories because of their potential to enable mass production of lightweight, fl exible and cost-effective devices. [ 1-4 ] Much of the focus has been on the development of polymer-based OPVs which have seen a dramatic rise in effi ciency over the last decade, and the encouraging power conversion effi ciency (PCE) over 9% has been achieved from bulk heterojunction (BHJ) OPVs based on polymer donors and fullerene acceptors. [ 5 ] Compared with their polymer counterparts, small molecules offer potential advantages in terms of defi ned molecular structure, defi nite molecular weight, easy purifi cation, easy mass-scale production, and good batch-to-batch reproducibility. [ 6-10 ] Recently, great efforts have been dedicated to develop small molecules for application in solar cells, such as linear molecules, [ 11-23 ] star-shaped molecules, [ 24-28 ] and other organic dyes; [ 29 , 30 ] and, so far, the highest PCEs of solution-processed OPVs based on small molecular donors and [6,6]-phenyl-C 61 (or C 71 )-butyric-acid-methyl-ester (PC 61 BM or PC 71 BM) acceptors are over 6% [ 15 , 17 ] and 7%, [ 19 , 20 ] respectively. Despite the fact that considerable progress has been made in small molecule-based OPVs, the relatively low PCE is hindrance to commercialization of these devices.© 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim.