Improved laser-induced forward transfer of organic semiconductor thin films by reducing the environmental pressure and controlling the substrate-substrate gap width

Laser-induced forward transfer (LIFT) has been investigated for bilayer transfer material systems: silver/organic film (Alq(3) or PFO). The LIFT process uses an intermediate dynamic release layer of a triazene polymer. This study focuses on the effect of introducing a controlled donor-receiver substrate gap distance and the effect of doing the transfer at reduced air pressures, whilst varying the fluence up to similar to 200 mJ/cm(2). The gap between 'in-contact' substrates has been measured to be a minimum of 2-3 mu m. A linear variation in the gap width from 'in contact' to 40 mu m has been achieved by adding a spacer at one side of the substrate-substrate sandwich. At atmospheric pressure, very little transfer is achieved for Alq(3), although PFO shows some signs of successful doughnut transfer (with a large hole in the middle) in a narrow fluence range, at gaps greater than 20 mu m. For the transfer of Ag/PFO bilayers at atmospheric pressure, the addition of a PFO layer onto the receiver substrate improved the transfer enormously at smaller gaps and higher fluences. However, the best transfer results were obtained at reduced pressures where a 100% transfer success rate is obtained within a certain fluence window. The quality of the pixel morphology at less than 100 mbar is much higher than at atmospheric pressure, particularly when the gap width is less than 20 mu m. These results show the promise of LIFT for industrial deposition processes where a gap between the substrates will improve the throughput.