In summary, we developed the first deuterated exciplex-forming host (D-SiCzCz: D-SiTrzCz2) for deep-blue phosphorescent OLEDs in literature, derived from the previous reported promising SiCzCz: SiTrzCz2 exciplex-system. It was demonstrated that, besides the suppressed high-energy molecular vibrations and reduced chemical reactivity to improve the stability of materials, the deuteration could lower the molecular reorganization energy to improve carrier transporting capabilities of both donor and acceptor components. Moreover, deuteration was also found to enlarge the compactness of the host and thus provide a rigid environment to suppress the dopant deformation, consequently decreasing the shoulder emission intensity of the dopant for a bluer colour and accelerating the radiative decay process for a shorter lifetime of excited states meanwhile. The corresponding PhOLEDs displayed a dramatically longer lifespan of 370 h at an initial luminance of 1000 cd m -2 , which is 1.6 times longer than that of the control device, a reduced operational voltage and bluer CIE coordinates of (0.148, 0.165). All those performances represent one of the best results among deep-blue devices. Given the lack of sufficient attention on the deuteration of host materials, our work offered a valuable contribution, elucidating the impact of deuterated exciplexes and facilitating the advancement of stable and efficient blue OLEDs.