Inkjet printing offers a scalable and material-efficient route for fabricating organic light-emitting devices, yet solution-processed phosphorescent OLEDs (PHOLEDs) remain limited by interfacial instability, solvent incompatibility, and poor ambient processability. In this study, we report a high-performance, hole-transport layer (HTL)-free PHOLED fully fabricated under ambient conditions using an inkjet printing strategy based on eco-friendly solvents. A dual self-assembled monolayer (SAM) modification on the ITO anode, combining 2,3,4,5,6-pentafluorobenzoyl phosphonic acid and tricosafluorododecanoic acid, enables efficient charge injection without the need for conventional HTLs. Complementing this, a binary solvent system comprising environmentally benign components is engineered to suppress the coffee-ring effect and significantly improve film uniformity. Furthermore, a newly designed heteroleptic Ir(III) emitter with tailored solubilizing groups enhances ink compatibility and charge-transport properties. The resulting devices achieve a record-high external quantum efficiency of 16.8% under ambient processing conditions, marking a new benchmark for inkjet-printed PHOLEDs. This work demonstrates a synergistic approach to interfacial engineering and eco-conscious solvent design, offering a scalable, sustainable pathway toward high-efficiency, vacuum-free OLED technologies.