Organic lighting-emitting diodes (OLEDs) have steadily become one of the dominant display technologies, particularly in mobile devices, smartwatches and televisions, due to the inherent advantages of self-luminescence, the wide viewing angle, its low energy use and the capacity to fabricate flexible and transparent devices. Almost all commercialized OLEDs are fabricated by vacuum deposition as this technology has been shown to produce high-quality, high-performance devices, in part due to the performance of materials specifically designed to be processed by vacuum thermal evaporation. Compared to this fabrication process, solutionprocessed OLEDs (SP-OLEDs), especially those based on ink-jet printing technology, have distinct advantages associated with a much lower production cost, a more facile fabrication process for large-area devices, and a lower level of wasted material. Historically, however, SP-OLEDs tended to show poorer performance than vacuum-deposited OLEDs (VD-OLEDs) in terms of their luminescence efficiency, device lifetime, and color purity. This is in part due to sub-optimal materials performance and design. Developing new materials specifically targeted for SP-OLEDs remains an outstanding academic and industry research challenge.