Solution and Evaporation Hybrid Approach to Enhance the Stability and Pattern Resolution Characteristics of Organic Light-Emitting Diodes

Abstract

The solution process and vacuum evaporation, both fabrication methods for conventional organic light-emitting diodes (OLEDs), are intrinsically restricted with regard to their ability to enhance pattern resolutions and film stability outcomes. Here, we introduce a novel approach of the solution process followed by intense pulsed light (IPL) evaporation for producing high-resolution line patterns of OLEDs. Through control of the wettability between the banks and microchannels via a mask-free selective surface treatment, we successfully deposited phosphorescent green and red inks only into the microchannels. Then, high-resolution patterns of an emitting layer (EML) layer were uniformly evaporated onto the device substrate using IPL evaporation. Ultimately, we fabricated green and red phosphorescent OLED devices with a high pixel density of a line-patterned EML with a width of 6 μm and a pitch of 13.6 μm. In addition, we demonstrated that the IPL-evaporated films have many advantages compared to those fabricated by the conventional solution process. We also showed that the IPL evaporation process can be less sensitive to problems related to the aggregation of organic molecules during a drying or annealing process. Hence, the device performance and lifetime of the IPL-evaporated OLEDs were enhanced compared to those of the spin-coated OLEDs.

Role of Guest Materials in the Lower Stability of Solution-Coated versus Vacuum-Deposited Phosphorescent OLEDs

“…The commercialization of organic light-emitting devices (OLEDs) based on vacuum-deposited (VAC) small molecules has seen rapid progress in the last 10 years . However, the use of vacuum deposition has several drawbacks, including a low utilization yield of materials and high manufacturing costs. , Using solution-coating methods in device fabrication can overcome these issues and provide benefits especially for large-area products. ,, Such solution-coated (SOL) devices, however, have significantly shorter electroluminescence (EL) lifetimes when compared to their VAC counterparts. ,− …”

Solution-processable donor–π–acceptor type thieno[3,2-b]thiophene derivatives; synthesis, photophysical properties and applications

“…Although several small materials have been applied for OLEDs fabricated by vacuum-evaporation technology, most of them are not suitable for solution processing methods on account of inadequate solubility and crystallization tendency problems. [11][12][13][14] In addition to the solution-processability of small molecules, efficient charge injection and charge transport balance are also very important for the performance of solutionprocessed device fabrications. [15][16][17] In order to obtain strong intramolecular charge transfer (ICT), push-pull heteroaromatic p-conjugated systems, which are a significant method of adjusting the electronic properties, are well-known models, such as donor-acceptor (D-A) and donor-p bridge-acceptor (D-p-A) systems.…”

“…Although several small materials have been applied for OLEDs fabricated by vacuum-evaporation technology, most of them are not suitable for solution processing methods on account of inadequate solubility and crystallization tendency problems. 11–14…”

Dewetting‐Assisted Patterning of Organic Semiconductors for Micro‐OLED Arrays with a Pixel Size of 1 µm

“…Currently, the rigid shadow mask patterning in the mainstream technology for OLEDs (i.e., vacuum deposition) has been challenged for microscale arrays due to the gap and mismatch of thermal expansion coefficients between the substrate and the shadow mask. [14] The resolution of typical micro-OLEDs obtained using the mask patterning method is limited to ≈30 µm. [15] Although lithographical patterning approach can readily achieve a resolution of micrometers, they cannot be simply applied to the inherently instable organic materials for micro-OLEDs.…”