Perovskite heteroepitaxy for high-efficiency and stable pure-red LEDs

Ultrasmall CsPbI₃ perovskite quantum dots (QDs) are the most promising candidates for realizing efficient and stable pure-red perovskite light-emitting diodes (PeLEDs)^1-5. However, it is challenging for ultrasmall CsPbI₃ QDs to retain their solution-phase properties when they assemble into conductive films, greatly hindering their device application^3,6. Here we report an approach for in situ deposit stabilized ultrasmall CsPbI₃ QD conductive solids, by constructing CsPbI₃ QD/quasi-two-dimensional (quasi-2D) perovskite heteroepitaxy. The well-aligned periodic array of edge-oriented ligands at heterointerface triggers a substantial octahedral tilting in a critical layer thickness of CsPbI₃ QDs, which heightens the Gibbs free energy difference between the tilted-CsPbI₃ and δ-CsPbI₃ leading to thermodynamic stabilization of CsPbI₃ QDs. The approach allows us to fabricate stabilized CsPbI₃ QD conductive films with tunable emission covering the entire red spectral region from 600 nm to 710 nm. Here we report the pure-red PeLEDs with narrow electroluminescence peak centred at 630 nm, matching the Rec. 2100 standard for ultrahigh-definition display. The champion device exhibits a certified external quantum efficiency of 24.6% and a half-lifetime of 6,330 min, ranking as one of the most efficient and stable pure-red PeLED reported to date. The approach is also compatible with large-area manufacturing, enabling 1 cm² PeLED to exhibit the best external quantum efficiency of 20.5% at 630 nm.