We present all-solution processed, indium tin oxide-free organic solar cells on mechanically flexible polyethylene terephthalate (PET) substrates with power conversion efficiencies up to 4.8%. The mechanical properties of the devices are dictated by the electrodes from either metal-organic silver inks or a combination of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) and silver nanowires. Both electrodes can sustain high tensile strains. The influence of mechanical strain on the solar cell performance was experimentally studied in situ by measuring the J-V curves of elongated samples under illumination. At a strain of 14%, we still observed 90% of the initial device power output. At higher strain, crack formation within the electrodes was identified as the origin for device failure. (C) 2014 Elsevier B.V. All rights reserved.