Close-space sublimation (CSS) has been considered as a cost-effective, alternative deposition method to conventional line-of-sight deposition techniques, such as the linear source, in the production of OLED displays. In the CSS process, a donor sheet pre-coated with OLED materials is utilized as a planar source and, upon heating, transfers these materials to a receiver substrate held in proximity to form an organic thin film. Owing to its unique configuration, CSS has demonstrated numerous advantages, such as high material utilization, short process time, and multi-component co-deposition. Despite its great potential, CSS has yet to be reduced to practice in manufacturing because OLED devices fabricated by CSS generally show inferior performance to the devices made by conventional metho...[ Read more ]

Close-space sublimation (CSS) has been considered as a cost-effective, alternative deposition method to conventional line-of-sight deposition techniques, such as the linear source, in the production of OLED displays. In the CSS process, a donor sheet pre-coated with OLED materials is utilized as a planar source and, upon heating, transfers these materials to a receiver substrate held in proximity to form an organic thin film. Owing to its unique configuration, CSS has demonstrated numerous advantages, such as high material utilization, short process time, and multi-component co-deposition. Despite its great potential, CSS has yet to be reduced to practice in manufacturing because OLED devices fabricated by CSS generally show inferior performance to the devices made by conventional methods. It is therefore imperative to fully establish the evaporation characteristics of OLED materials used in the CSS process and to assess the morphological, photoluminescent and electrical properties of CSS-deposited films as a function of CSS process conditions.

This thesis is focused on the development of a CSS process suitable for the fabrication of blue OLED devices. Two different CSS setups, one using a thin Ta foil as the resistive heating donor and the other using a Si wafer as the IR-absorbing donor, were devised to carry out CSS experiments. Their system design, work principle, and experimental verifications are discussed in detail. More importantly, the CSS processes for the deposition of a series of amine-based blue dopants and a hydrocarbon blue host, which resemble the composition of the blue emitters used in commercial products, were thoroughly examined. The aim is to identify a host-dopant pair that can be evaporated simultaneously in CSS without segregation to produce a uniformly doped emitter layer. The device performances of selected blue host-dopant pairs deposited under various CSS conditions were evaluated. Furthermore, the CSS deposition with fine shadow masks was simulated by numerical calculation to illustrate the patterning capability of CSS as a function of mask dimensions and CSS configurations. Design principles of CSS setups and shadow masks for patterning ultrahigh-resolution OLED displays are proposed.