Laser-Induced Forward Transfer of Organic LED Building Blocks Studied by Time-Resolved Shadowgraphy

The patterned deposition of thin films is essential for many technological applications. One promising material deposition technique is laser-induced forward transfer (LIFT), where a thin layer coated oil a transparent substrate is ablated by it laser pulse passing through the substrate. The ablated material is collected on a nearby receiver substrate in a pattern defined by the laser. The technique can be applied to heat and light sensitive materials, provided that they are not directly irradiated by the laser pulse. For this application, a sacrificial layer is introduced between the substrate rind the transfer layer so that the laser energy is converted into mechanical propulsion while protecting the sensitive layer from radiation. In this work, the application of a triazene polymer as it sacrificial layer for LIFT has been studied with the final goal of transferring organic light-emitting diode (OLED) pixels. Donor films made of it stack of triazene polymer, metal, and optionally an electroluminescent polymer were irradiated from the back side by a pulsed XeCl excimer laser (308 rim, 30 ns), and the ablation process was imaged by lateral tune-resolved shadowgraphy. Back-side ablation of it triazene/metal film produced the ejection of a metal flyer, whose stability in flight can be improved when the flyer contained a layer of undecomposed triazene polymer. The stabilization was provided by the composite structure of the metal/polymer film. A receiver substrate was placed at distances of 0.5 and 1 min to collect the pixel. However, the transfer across the gap revealed an effect that complicates the system. The shock wave created by ablation was reflected from the receiver substrate and may cause the destruction of the flyer. Transfer studies in a vacuum showed that the shock wave can be eliminated but that the flyer speed increased substantially, leading to the disintegration of the flyer upon impact with the receiver Substrate. The ejection of a flyer from a triazene/metal/luminescent polymer film, selected as a building block of an OLED pixel, shows an increased stability of the flyer as well, thus confirming the strengthening effect of a polymer layer on the metal flyer. Using this system. the transfer in air of incomplete pixels showed promise, opening the way to patterned deposition without contact between the substrates.