Triazatruxene-Diketopyrrolopyrrole Dumbbell-Shaped Molecules as Photoactive Electron Donor for High-Efficiency Solution Processed Organic Solar Cells

Photovoltaic solar energy conversion has attracted considerable interest of the scientifi c community due to the urgent need for alternative and renewable energy sources. Solar cells using solution-processed organic semiconductors as a photoactive layer have appeared as a particularly promising technology due to the prospective for low cost, light weight modules and roll-to-roll processing. [ 1 ] A signifi cant increase in the power conversion effi ciency (PCE) of solution-processed organic photovoltaic (OPV) devices has been achieved over the last decade, and results largely from the development of new electron-donating conjugated polymers. Intensive research on solution-processed small conjugated molecules, as an alternative to semiconducting polymers, started more recently and is driven by potential advantages, such as the mono-disperse nature, easier purifi cation, better reproducibility and excellent light-harvesting properties of molecular dyes. Small molecules have already been used effi ciently in vapor-deposited OPV devices and allowed the development of tandem cells with PCEs around 12%. [ 2 ] For solution-processed devices, however, the performances are still lower and limited by the diffi-culty in achieving high quality thin fi lms with a controlled and thermally stable nanomorphology (interpenetrated network of donor and acceptor domains), good charge carrier transport and low recombination rates.© 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim.