Metal halide perovskites are an emerging class of solution processable materials that have exhibited remarkable optoelectronic properties, such as high carrier mobility 1 , long diffusion length 2,3 , bandgap tunability 4,5 , high luminescence efficiency 6 and narrow emission bandwidth 7 . These properties, along with the ease of preparation of halide perovskite materials, have led to great advances in applications such as solar cells [8][9][10][11] , photodetectors 12,13 and light-emitting diodes (LEDs) [14][15][16][17] . The development of perovskite LEDs (PeLEDs) has, in particular, been rapid: in 2014 we reported electroluminescence (EL) from halide perovskites 14 and by 2018 we and others had achieved external quantum efficiencies of >20% 18-21 .

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Reducing environmental impact is a key challenge for perovskite optoelectronics, as most high-performance devices are based on potentially toxic lead-halide perovskites. For photovoltaic solar cells, tin-lead (Sn–Pb) perovskite materials provide a promising solution for reducing toxicity. However, Sn–Pb perovskites typically exhibit low luminescence efficiencies, and are not ideal for light-emitting applications. Here we demonstrate highly luminescent germanium-lead (Ge–Pb) perovskite films with photoluminescence quantum efficiencies (PLQEs) of up to ~71%, showing a considerable relative improvement of ~34% over similarly prepared Ge-free, Pb-based perovskite films. In our initial demonstration of Ge–Pb perovskite LEDs, we achieve external quantum efficiencies (EQEs) of up to ~13.1% at high brightness (~1900 cd m−2), a step forward for reduced-toxicity perovskite LEDs. Our findings offer a new solution for developing eco-friendly light-emitting technologies based on perovskite semiconductors.