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Solution-processed light-emitting diodes (LEDs) based on copper–iodide clusters are promising candidates for solid state lightings due to their abundance, environmental friendliness and high luminescent efficiency. However, the development of this class of LEDs is hampered by the instability of the clusters, poor solution compatibility and low film quality, resulting in poor device performances. Here we report a new type of copper–iodide cluster hybrids with functional groups that facilitate both solubility and stability of the clusters. The hybrid clusters exhibit high structural stability in solvents, enabling smooth solution-processed thin films with low surface roughness of 0.22 nm and high photoluminescence quantum yields of over 70%. We employ the high-quality thin film as an emissive layer in warm-white LEDs, showing a maximum external quantum efficiency of 19.1%, maximum high brightness of over 40,000 cd m−2and a good operational lifetime of 232 h (T50at an initial luminance of 100 cd m−2). We also demonstrate a large-area LED with brightnesses of up to ~60,000 cd m−2through blade-coating and a series of colour-tunable LEDs based on ligand modifications. Our results suggest great potential of copper–iodide cluster-based LEDs for practical applications in panel display and solid-state lighting.