Binary-Solvent-Programmed Single-Step Inkjet Printing of Self-Confined Micro-Inlaid OLED Arrays

Inkjet printing offers a mask-free route to large-area electronics, yet achieving uniformity in micron-scale organic light-emitting diode (µ-OLED) arrays remains challenging. Presented here is a photolithography-free, solvent-programmed, single-step inkjet micro-inlay process in which lateral phase separation self-confines each emissive pixel. Guided by solubility parameters, a trichloromethane (TCM)/1,2-dichloroethane (DCE) binary solvent is designed to optimize interactions among the solvents, emissive solutes, and the poly(4-vinylpyridine) (P4VP) underlayer. Micro-Raman mapping, cross-sectional SEM, and AFM phase analysis support lateral phase separation between the emissive region and the displaced P4VP phase, selective restructuring of P4VP while preserving the underlying transport layer, and no detectable nanoscale phase segregation within the emissive interior, yielding self-confined pixels of approximately 100 µm. High-speed imaging shows that the blend yields reproducible 180 dpi arrays without jetting instability or nonuniform deposition. Green µ-OLED arrays printed with the blend achieve a peak luminance of 2400 cd m^-2, a peak current efficiency of 3.5 cd A^-1, and a peak external quantum efficiency of 1.0%. The figure of merit and luminance uniformity improve by 2.6- and 6.9-fold, and by 3.9- and 2.9-fold, respectively, relative to neat TCM and neat DCE. This strategy enables scalable fabrication of flexible and three-dimensional conformal OLED platforms.