H-aggregated small molecular nanowires as near infrared absorbers for organic solar cells

Near infrared absorber materials for organic solar cells are needed to cover larger parts of the solar spectrum and, therefore, achieve higher short circuit current densities. We present a push-pull chromophore with a quinoid merocyanine structure (QM1) as donor material in vacuum deposited organic solar cells with a thin film absorption up to 1100 nm. A blue shift of the main absorption peaks of the thin film as compared to the solution indicates H-aggregation of the material. Morphology investigations using scanning electron microscopy and electron diffraction reveal a crystalline growth in nanowires, with lengths of hundreds of nanometers to a few micrometers, and diameters of a few tens of nano-meters. Organic solar cells incorporating a blend of QM1 with C-60 reach power conversion efficiencies up to 1.9% under 1 sun illumination with an external quantum efficiency of over 18% from 600 nm to 1000 nm. (C) 2017 Elsevier B.V. All rights reserved.