ITO-free laminated concept for flexible organic solar cells

• A concept for ITO-free laminated organic solar cells on flexible foils is presented.
• Offers freedom of choice of materials and deposition techniques for electrodes.
• Done with simple lamination rolls making it attractive for roll-to-roll processing.
• Efficiencies of 2.5% were achieved for laminated P3HT:PCBM organic solar cells.
• Over 80% of the reference device efficiency on a single substrate.

In this paper, we present laminated concept for indium tin oxide (ITO)-free organic solar cells (OSC). This concept omits the need of electrode deposition on top of organic layers and thus gives freedom of choice for the electrodes and the corresponding deposition techniques to achieve the best ratio between material consumption and electrical/optical properties. Various lamination processes have already been conducted on organic solar cells, mainly hot press lamination in which the lamination is done under high pressure in preheated conditions for several minutes. Here a new concept is presented where the polyethylene terephthalate (PET) flexible foils with organic layers are laminated without the use of high pressure and/or temperature and are just passed through simple lamination rolls. This use of simple lamination rolls and elimination of high pressure and temperature during lamination makes this concept a significant step closer to roll to roll (R2R) compatible. Furthermore the transparent contact was formed by a silver (Ag) grid and highly conductive Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) to replace ITO. To our best knowledge, this is the first ITO-free laminated concept on flexible foils which additionally eliminates the use of high pressure lamination. For a laminated organic solar cell with poly(3-hexylthiophene) (P3HT): (6,6)-phenyl C61 butyric acid methyl ester (PCBM) as photoactive layer, experimental results have shown a device efficiency of 2.5% on an active area of 1.1 cm2 which is more than 80% of the reference device efficiency with similar device architecture on a single substrate.

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