ITO-free organic solar cells with roll-to-roll coated organic functional layers from non-halogenated solvents

This work reports on indium tin oxide (ITO)-free organic solar cells with roll to roll (R2R) processed organic functional layers. The device stack comprises a chromium-aluminum-chromium (Cr-Al-Cr) electron contact layer on a polyethylene terephthalate (PET) film, a photoactive layer of poly(3-hexylthiophene) (P3HT): (6,6)-phenyl C61 butyric acid methyl ester (PCBM), a hole transport layer of Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) and a silver (Ag) grid for current collection. For the photoactive layer the non-halogenated solvent o-Xylene was used in order to reduce the impact on health and environment for R2R coating on ambient atmospheric conditions. The Cr-Al-Cr layers were sputtered onto the PET rolls in a batch process while the photoactive layer as well as the hole transport layer were applied in a continuous R2R process by slot die coating. The Ag grid was either thermally evaporated through a shadow mask as reference process or deposited by aerosol printing as a more production compatible process. Device efficiencies up to 2.9% on an active area of 1.1 cm2 were obtained with no difference for the method of grid processing. These experimental results demonstrate that R2R coated organic functional layers in ITO-free devices obtain the same device performance as compared to spin coated laboratory cells.