Lead halide perovskites have been considered promising semicon-ducting materials for next-generation optoelectronic devices due to their solution processability and excellent optoelectronic proper-ties. Device performance of perovskite light-emitting diodes (PeLEDs) and perovskite solar cells (PSCs) has been rapidly devel-oped during the past decade. Very recently, organic molecules containing phosphine oxide groups have emerged as promising ad-ditives and passivators to improve the device performance and sta-bility of both PeLEDs and PSCs. In this perspective, we summarize recent progress in the development of new phosphine-oxide-based additives for PeLEDs and PSCs. The passivation mechanism, molecule design principle, and structure-property relationship of phosphine oxide molecules for PeLEDs and PSCs are systematically discussed and analyzed. Finally, we provide an outlook on the mo-lecular design of novel phosphine oxide compounds for efficient and stable PeLEDs and PSCs in the future.