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 (similar to 20 nm to 1 mu m) 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-benzo-thiadiazole) (TFB/F8BT) and poly(3-hexylthiophene)/methanofullerene([6,6]-phenyl C-61 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.