<p>Organic light-emitting diodes (OLEDs) represent a revolutionary technology that has been successfully commercialized in full-colour displays. However, this technology is still severely limited by the low efficiency of blue OLEDs. Developing high-performance blue OLEDs is a major challenge, and emitters are critical for overcoming this issue. Here we design phosphorescent platinum(<span>ii</span>) complexes with a locally excited-dominated character and a rigid three-dimensional geometry to suppress intermolecular interactions, enabling robust deep-blue devices. Bottom-emitting OLEDs emit at 464 nm with a full-width at half-maximum of 17.1 nm and high external quantum efficiencies of 30.8%, 26.4% and 23.2% at 1,000 cd m⁻², 5,000 cd m⁻² and 10,000 cd m⁻², respectively. Top-emitting devices achieve enhanced colour purity (full-width at half-maximum of 13.1 nm, CIE_<i>y</i> = 0.062), a low running voltage (3.9 V at 1,000 cd m⁻²) and a maximum blue index of 468 cd A⁻¹ CIE_<i>y</i>⁻¹. These OLEDs also exhibit a long half-lifetime of 670 h at an initial luminance of 1,000 cd m⁻². This study provides an important strategy to develop high-performance deep-blue phosphorescent OLEDs.</p>