<p>Perovskite quantum dots (PQDs) hold great potential for brain-like neuromorphic computing. However, the development of PQDs-based synaptic devices is hindered by interfacial defects and limited stability. Here, we demonstrate a high-performance Cs₂AgBiBr₆ QDs/organic single crystal heterojunction synaptic device, fabricated via a novel space-confined vertical growth technique combined with a polymer-free transfer process. Vertically grown organic single crystals enable superior carrier mobility and facilitate the formation of low-defect interfaces with PQDs. The heterojunction exhibits remarkable photosensitivity (7.22 × 10⁵ at 425 nm) and detectivity (2.15 × 10¹⁵ Jones), owing to the strong optical absorption of PQDs coupled with the superior charge transport characteristics of organic single crystals. Notably, the device achieves dual-functional light adaptation, emulating synaptic behaviour under blue light while exhibiting photo-switching under green/red light. This unique capability enables smart blue-light hazard protection. This work not only provides a versatile platform for high-performance PQDs-based synaptic devices but also advances the development of brain-inspired neuromorphic systems for next-generation computing and intelligent sensing.</p>