Ultrastable Films Could Boost OLED Performance
A research team from Spain and Germany has now offered a surprisingly simple way to boost both OLED efficiency and stability by 15 percent or possibly much more, across a range of OLED devices and without a change in materials or device architecture. Instead, the multinational team’s approach focuses on adjusting the deposition temperature for the films that host the functional layers in a wide variety of OLEDs, to improve the films’ thermodynamic stability. The technique’s simplicity and generality, the researchers believe, could allow it to be leveraged to maximize the OLED performance, no matter which specific materials are used.
It’s the glass (transition)
The research team in the recently published work looked at another variable: how the organic layers in OLEDs are actually grown. In thinking about the question, the researchers took their cue from recent work in physical vapor deposition, the predominant technique for laying down OLED layers. That work showed that ultrastable glass films—which sport higher thermal and kinetic stabilities and a host of other thermodynamic pluses—could be formed by slowing down the deposition process and performing it at a temperature of around 85 percent of the substrate’s glass-transition temperature.
Boosting longevity and brightness
The team found that for both parameters, OLEDs including any of four different phosphorescent emitters and made using ultrastable glasses showed a greater than 15 percent enhancement relative to reference devices made with conventionally quenched films. And for some samples the improvement was far better. The blue test OLED, for instance, sported an EQE value 163 percent higher than the reference device; green and red OLED samples clocked LT70 lifetimes some 86 to 119 percent longer (or more) than the reference samples.
For OLEDs and beyond
The researchers also undertook a detailed analysis to determine just why the use of ultrastable glass boosted the device’s quantum efficiency. They were able to rule out effects such as temperature-dependent differences in the orientation of the emitters’ dipole moments and other factors. Instead, the work suggests, the enhancement in EQE traced to differences in exciton dynamics at the nanoscale that lead to a better radiative efficiency for the emissive layer.