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<p>High-boiling solvents are essential for inkjet-printed phosphorescent organic light emitting diodes (PHOLED), but their low vapor pressure leaves residual molecules that form dipolar sites, inducing polaron formation and quenching triplet emission. To overcome this, we introduced a vacuum-assisted annealing (VAA) strategy that removes &gt; 80% of ethyl p-toluate and &gt; 75% of 3-ethylbiphenyl from Ir(mppy)<sub>3</sub>-doped green PHOLED films. Efficient solvent removal was confirmed by mass spectroscopy, and photoluminescence decay indicated an extended triplet lifetime. Moreover, nanoscale surface analysis and absorption spectroscopy verified that VAA preserves film uniformity, smoothness, and the electronic structure of the Ir(III) complex. As a result, VAA-treated PHOLEDs achieved an external quantum efficiency (EQE) of 6.4%, a 75% improvement over spin-coated references. Under fully ambient inkjet-printing, devices also reached 4.4% EQE, representing a 30% gain compared to untreated films. This study demonstrates that residual solvent removal is the key bottleneck in printed PHOLEDs and establishes VAA as a simple, polymer-compatible strategy to enhance device performance under ambient, large-area processing conditions.</p> Graphical abstract <p>Vacuum-assisted annealing (VAA) effectively eliminates residual of high-boiling-point ethyl p-toluate and 3-ethylbiphenyl solvent from the phosphorescent EML processed under ambient conditions. This process removes dipolar solvent pockets, thereby preserving the emission characteristics and enhancing film uniformity. This increases the external quantum efficiency of VAA-based devices by 75% (from 3.7 to 6.4%), identifying residual solvent as the primary constraint for enabling an ambient and scalable fabrication process.</p> <p></p>

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Solvent engineering and vacuum annealing synergy for efficient ambient inkjet-printed PHOLEDs

  • 期刊论文

  • 发表日期：

    2025年10月17日

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  • Sagnik Chowdhury,
  • Keum-Jin Ko,
  • Vinayak Vitthal Satale,
  • Weiyang Zhou,
  • Jae-Wook Kang

摘要

High-boiling solvents are essential for inkjet-printed phosphorescent organic light emitting diodes (PHOLED), but their low vapor pressure leaves residual molecules that form dipolar sites, inducing polaron formation and quenching triplet emission. To overcome this, we introduced a vacuum-assisted annealing (VAA) strategy that removes > 80% of ethyl p-toluate and > 75% of 3-ethylbiphenyl from Ir(mppy)3-doped green PHOLED films. Efficient solvent removal was confirmed by mass spectroscopy, and photoluminescence decay indicated an extended triplet lifetime. Moreover, nanoscale surface analysis and absorption spectroscopy verified that VAA preserves film uniformity, smoothness, and the electronic structure of the Ir(III) complex. As a result, VAA-treated PHOLEDs achieved an external quantum efficiency (EQE) of 6.4%, a 75% improvement over spin-coated references. Under fully ambient inkjet-printing, devices also reached 4.4% EQE, representing a 30% gain compared to untreated films. This study demonstrates that residual solvent removal is the key bottleneck in printed PHOLEDs and establishes VAA as a simple, polymer-compatible strategy to enhance device performance under ambient, large-area processing conditions.

Graphical abstract

Vacuum-assisted annealing (VAA) effectively eliminates residual of high-boiling-point ethyl p-toluate and 3-ethylbiphenyl solvent from the phosphorescent EML processed under ambient conditions. This process removes dipolar solvent pockets, thereby preserving the emission characteristics and enhancing film uniformity. This increases the external quantum efficiency of VAA-based devices by 75% (from 3.7 to 6.4%), identifying residual solvent as the primary constraint for enabling an ambient and scalable fabrication process.