Infrared study on the molecular orientation in bulk-heterojunction films based on perylene and 3,4,9,10-perylenetetracarboxylic dianhydride

► We study molecular orientation in perylene-PTCDA blend films using infrared spectroscopy. ► PTCDA molecules take face-on orientation over a wide range of PTCDA contents from 7.5 to 88 mol%. ► Orientation of perylene molecules changes from edge-on toward random as the PTCDA content increases.