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Abstract Electrically driven light‐emitting diodes (ED LEDs) based on 3D metal halide perovskites have seen remarkable advancements during the past decade. However, the highest‐performing devices are largely based on lead‐containing 3D perovskites, presenting two key challenges – toxicity and stability – that must be addressed for commercialization. Reducing structural dimensionality and incorporating non‐lead metals present promising pathways to address these issues. Although research on ED LEDs based on low‐dimensional, lead‐free metal halides (LD LFMHs) is growing, their performance still significantly lags behind that of 3D lead halide perovskites. This review seeks to deliver a comprehensive overview of ED LEDs based on LD LFMHs, covering a brief history of their development, methods for material synthesis, luminescence mechanisms, and applications in electroluminescent devices. It also examines current challenges and proposes practical strategies to enhance device performance, with the goal of inspiring further progress in the field. 

A series of Ag( i ) and Cu( i ) complexes [Ag 3 (L 1 ) 2 ][PF 6 ] 3 ( 8 ), [Ag 3 (L 2 ) 2 ][PF 6 ] 3 ( 9 ), [Cu(L 1 )][PF 6 ] ( 10 ) and [Cu(L 2 )][PF 6 ] ( 11 ) have been synthesized by reactions of the tridentate amine-bis(N-heterocyclic carbene) ligand precursors [H 2 L 1 ][PF 6 ] 2 ( 6 ) and [H 2 L 2 ][PF 6 ] 2 ( 7 ) with Ag 2 O and Cu 2 O, respectively. Complexes 10 and 11 can also be obtained by transmetalation of 8 and 9 , respectively, with 3.0 equiv. of CuCl. A heterometallic Cu/Ag–NHC complex [Cu 2 Ag(L 1 ) 2 (CH 3 CN) 2 ][PF 6 ] 3 ( 12 ) is formed by the reaction of 8 with 2.0 equiv. of CuCl. All complexes have been characterized by NMR, electrospray ionization mass spectrometry (ESI-MS), and single-crystal X-ray diffraction studies. The luminescence properties of 10–12 in solution and the solid state have been studied. At room temperature, 10–12 exhibit evident luminescence in solution and the solid state. The emission wavelengths are found to be identical at 483 nm in CH 3 CN, but they are 484, 480 and 592 nm in the solid state for 10–12 , respectively. These results suggest that 12 dissociates into two molecules of 10 and Ag( i ) ions in solution. Complex 12 is the first luminescent heterometallic Cu/Ag–NHC complex.