Combinatorial optimization of evaporated bilayer small molecule organic solar cells through orthogonal thickness gradients

We report on a combinatorial optimization procedure applied to heterojunction small molecule organic solar cells made of evaporated copper phthalocyanine (CuPc) and 3,4,9,10-perylenetetracarboxylic bisbenzimidazole (PTCBI). Our strategy consists of depositing both light harvesting compounds as orthogonally arranged wedge-shaped layers to then determine the optimum thicknesses which yield the highest photoconversion efficiency. The device performance is locally assessed by means of light-beam induced current images. A quantitative model of co-locally measured Raman images allows determining the corresponding local thicknesses of the active layers. The spatial correlation of both datasets (i.e. local photocurrent density and active layer film thicknesses) enables the rapid optimization of the photovoltaic system studied employing a single functional device, reducing in approximately 20 times the use of resources and time.