There are significant challenges in designing suitable device architectures for deep-blue OLEDs. The high triplet energy and shallow LUMO energy of the emitters mean that there are very few suitable hosts, most deep-blue OLEDs use the phosphine oxide-based hosts TSPO1 or DPEPO. There are several issues with the use of DPEPO including poor hole transporting ability and its inherent instability. In the context of being limited to the use of this class of host, in order to improve the performance of deep-blue OLEDs there are a number of device architectures that can be used to partially overcome the deficiencies of the available hosts. For instance, to improve charge balance in the emissive layer (EML) high concentrations of emitter can be used as the emitter can act as a hole transporting material, this approach can be very successful, although only when the emitter doesn't undergo aggregation-caused quenching. Constraining the excitons within the emissive layer of the OLED is possible with the use of the emitter itself as an exciton blocking layer. The poor device lifetime of phosphorescent deep-blue OLEDs presents a significant hurdle to their adoption in commercial displays. Unfortunately, device lifetimes are rarely reported in the academic literature; 33 however, degradation of blue OLEDs has been studied. Several degradation mechanisms have been identified, including via triplet-triplet annihilation (TTA), triplet-polaron annihilation (TPA) and chemical degradation of the emitter. Knowledge of these degradation mechanisms has been used to guide the design and choice of host materials and device structures leading to a steady improvement in device performance. This is exemplified by cross-comparing device lifetimes using the same Ir(cb)3 emitter (Figure ). The first reported OLED using this emitter showed an EQEmax of 24.8% with a described short device lifetime. Jung et al. demonstrated that the device lifetime could be significantly enhanced to LT50 > 10 000 h at 100 cd m -2 by optimizing the charge balance within the EML by using the bipolar host SiCzTrz. The blue OLEDs [λEL = 471 nm and CIE coordinates of (0.12, 0.13)] also showed excellent efficiency and low efficiency roll-off with EQEmax of 27.6% that decreased slightly at 1000 cd m -2 to 25.6%.