Light‐Emitting Microinlaid Spots Produced through Lateral Phase Separation by Means of Simple Single‐Inkjet Printing

Abstract

High‐performance solution‐processable light‐emitting diodes (LEDs) attract much research interest due to the very high complexity of conventional vacuum‐processed LEDs. A simple single‐inkjet‐printing process using a phase‐separable material combination is presented. With single‐inkjet printing of an ink containing semiconducting compounds on a phase‐separable insulating layer, convective and Marangoni flows in sessile droplets can produce microinlaid spots through the site‐selective etching of the insulating layer and the simultaneous self‐filling of the semiconductors in the etched vacancies. As a proof of concept, microinlaid organic LEDs (OLEDs) with a spatial resolution of ≈200 dpi in a phase‐separable poly(4‐vinylpyridine) layer without any conventional preformation of bank‐like structures are produced. The fabricated green microinlaid OLEDs exhibit excellent performance with maximum brightness of ≈13 000 cd m−2 and maximum efficiency of ≈14.2 cd A−1. Moreover, large‐area inkjet‐printed OLEDs are simply realized using the microinlaid spot arrays. These results demonstrate that the inkjet‐inlay structure is a promising candidate for high‐performance next‐generation solution‐processable LEDs.

Interphase-Controlled Inkjet Printing of MicroInlaid OLEDs: Effects of Solvent– and Solute–Polymer Interactions

“…Site-selective etching of the P4VP insulating layer and the simultaneous infilling of CBP into the vacancies in the P4VP layer via lateral phase separation produced microinlaid spots by the single-step inkjet printing process. 43 Micro-Raman measurements confirmed the formation of the microinlaid spot structures of CBP through the P4VP layer, differing from conventional comixed CBP spots within insulating poly(methyl methacrylate) (PMMA) layers. 42 Based on these studies, the importance of the interaction between functional solutes and a phase-separable insulating polymer has been elucidated and emphasized as a key parameter when aiming to create microinlaid spots by means of single-step inkjet printing.…”

“…One promising method involves incorporating a functional material layer into a single-step inkjet printing process. 42,43 The authors recently presented a simple single-step inkjet printing process that utilizes simultaneous inkjet etching and infilling steps realized by a phase-separable material system involving functional materials with different solubility properties. 43 This material system was composed of poly(4vinylpyridine) (P4VP) as an insulating polymer and semiconducting 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) as a functional compound.…”

“…42,43 The authors recently presented a simple single-step inkjet printing process that utilizes simultaneous inkjet etching and infilling steps realized by a phase-separable material system involving functional materials with different solubility properties. 43 This material system was composed of poly(4vinylpyridine) (P4VP) as an insulating polymer and semiconducting 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) as a functional compound. Site-selective etching of the P4VP insulating layer and the simultaneous infilling of CBP into the vacancies in the P4VP layer via lateral phase separation produced microinlaid spots by the single-step inkjet printing process.…”

“…To the best of our knowledge, ours was the first report of a simple single-step inkjet printing process for high-performance microinlaid OLED arrays using a phase-separable material combination. 43 This OLED fabrication procedure unifies single-step inkjet-printing step of emissive layers (EML) with spin-coating and vacuum deposition steps for common layers, circumventing the need for complex bank-formation or intricate patterning steps. 43 This integrated approach enables precise patterning, minimizes waste, and offers adaptability across various substrates and scalability for mass production, thus presenting a cost-efficient alternative to conventional OLED patterning methods, highlighting a significant advancement in the field of OLED technology.…”

“…43 This OLED fabrication procedure unifies single-step inkjet-printing step of emissive layers (EML) with spin-coating and vacuum deposition steps for common layers, circumventing the need for complex bank-formation or intricate patterning steps. 43 This integrated approach enables precise patterning, minimizes waste, and offers adaptability across various substrates and scalability for mass production, thus presenting a cost-efficient alternative to conventional OLED patterning methods, highlighting a significant advancement in the field of OLED technology. 43 Even with advanced knowledge of solute-polymer interactions, it is still challenging to select an appropriate solvent to successfully create well-patterned microinlays with homogeneous thin layers of a specific phase-separable polymer.…”