Efficient Conjugated‐Polymer Optoelectronic Devices Fabricated by Thin‐Film Transfer‐Printing Technique

The fabrication of functional multilayered conjugated‐polymer structures with well‐defined organic‐organic interfaces for optoelectronic‐device applications is constrained by the common solubility of many polymers in most organic solvents. Here, we report a simple, low‐cost, large‐area transfer‐printing technique for the deposition and patterning of conjugated‐polymer thin films. This method utilises a planar poly(dimethylsiloxane) (PDMS) stamp, along with a water‐soluble sacrificial layer, to pick up an organic thin film (～20 nm to 1 µm) from a substrate and subsequently deliver this film to a target substrate. We demonstrate the versatility of this transfer‐printing technique and its applicability to optoelectronic devices by fabricating bilayer structures of poly(9,9‐di‐n‐octylfluorene‐alt‐(1,4‐phenylene‐((4‐sec‐butylphenyl)imino)‐1,4‐phenylene))/poly(9,9‐di‐n‐octylfluorene‐alt‐benzothiadiazole) (TFB/F8BT) and poly(3‐hexylthiophene)/methanofullerene(6,6]‐phenyl C₆₁ butyric acid methyl ester) (P3HT/PCBM), and incorporating them into light‐emitting diodes (LEDs) and photovoltaic (PV) cells, respectively. For both types of device, bilayer devices fabricated with this transfer‐printing technique show equal, if not superior, performance to either blend devices or bilayer devices fabricated by other techniques. This indicates well‐controlled organic‐organic interfaces achieved by the transfer‐printing technique. Furthermore, this transfer‐printing technique allows us to study the nature of the excited states and the transport of charge carriers across well‐defined organic interfaces, which are of great importance to organic electronics.