On the homogeneity of the external quantum efficiency in a free OPV roll-to-roll flexible solar module

We present a microscopic characterization of an organic photovoltaic (OPV) module demonstrator, fabricated within the "freeOPV" project. The local properties of the module are discussed on different length scales, from the submicrometric to the centimeters one, inferring the module structure and the origin of the different contributions to the optical and photoelectrical spatial inhomogeneity. We show that the local external quantum efficiency (EQE) in the individual cells of the module exhibits typical variations within 6-8% of the peak value over about 0.4 mm2. Larger variations are observed when comparing different cells across the module surface, with differences in the EQE peak values up to 1.6 times. Our results suggest that the roll-to-roll OPV module performance can be further improved by optimizing the printing uniformity as well as the charge extraction efficiency of electrodes.