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

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.