Spatial mapping of photocurrents in organic solar cells comprising wedge-shaped absorber layers for an efficient material screening

In this work we present a facile route to an efficient experimental screening of new materials and to a layer thickness optimization in solution processable polymer photovoltaic devices. Therefore, we developed a method of fabricating solar cells with wedge-shaped active layers. Spatially resolved measurements of the solar cell short circuit current densities for different light absorbing polymers under white light allow for a quick conclusion about the optimum active layer thickness within the device. To demonstrate the generality of this experimental approach we studied the well-established photoactive blends from poly-(3-hexylthiophene-2,5-diyl) and [6,6]-phenyl C61-butyric acid methyl ester (P3HT:PC61BM) or poly[N-9′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] and [6,6]-phenyl C71-butyric acid methyl ester (PCDTBT:PC71BM). The short circuit current densities are in very good agreement with optoelectronic device simulations and results from sample-by-sample measurements.

► New material- and time-efficient method for photocurrent optimization in organic photovoltaic devices.
► Method for material screening on very low quantities using wedge-shaped active layers.
► Exact pre-calculation of the wedge-shaped layer thickness from fluid dynamics.
► JSC dependency on the active layer thickness for P3HT:PC61BM and PCDTBT:PC71BM solar cells with a resolution below 10 nm.
► n- and k-values of PCDTBT measured with spectroscopic ellipsometry.