Inverted bulk heterojunction solar cells are fabricated using a conjugated polyelectrolyte (PFN) as a cathode interlayer. Enhanced photovoltaic performance is achieved by adjusting the PFN thickness. Measurements of the optical transmittance, cathode work function (via UPS) and surface atomic composition (via XPS) provide insights into this optimization. Drift-diffusion simulations point to a reduction in recombination of holes at the cathode as the main cause for improving Voc. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.