From Event: SPIE Organic Photonics + Electronics, 2017
Although the promise of realizing lower cost fabrication by means of solution-based processing techniques, such as spin coating, web coating or inkjet printing, has been one key driver behind the interest in OLEDs for the last two decades, the lower stability of devices made by these techniques has been a long standing issue. With recent advances in developing solution-processable small molecule materials, it is now possible to make OLEDs of the same small molecule materials by either solution coating or vacuum deposition. Despite this, there continues to be an intriguing stability gap.
In this work, we investigate this phenomenon with the purpose of identifying its root causes. Electroluminescence, delayed electroluminescence and photoluminescence measurements are used to study and compare between the aging behavior in OLEDs made by spin-coating versus vacuum-deposition. Hole-only devices are also utilized, and employed to study the effects of charges and excitons, separately and combined. The results reveal that the faster degradation of solution-processed devices relative to their vacuum-deposited counterparts under electrical stress is due to a faster molecular aggregation process. Excitons and interactions between them and polarons appear to play a leading role in inducing this phenomenon. Results from these investigations will be presented and discussed.
Hany Aziz, Yong Joo Cho, Hyeonghwa Yu, and Yingjie Zhang, "Investigating the causes of the lower stability of solution-coated versus vacuum-deposited small-molecule organic light emitting devices (Conference Presentation)," Proc. SPIE 10362, Organic Light Emitting Materials and Devices XXI, 103620R (Presented at SPIE Organic Photonics + Electronics: August 07, 2017; Published: 19 September 2017); https://doi.org/10.1117/12.2276696.5581151948001.
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