Stable Light-Emitting Diodes Using Phase-Pure Ruddlesden-Popper Layered Perovskites

State-of-the-art light-emitting diodes (LEDs) are made from high-purity alloys of III-V semiconductors, but high fabrication cost has limited their widespread use for large area solid-state lighting. Here, efficient and stable LEDs processed from solution with tunable color enabled by using phase-pure 2D Ruddlesden-Popper (RP) halide perovskites with a formula (CH₃ (CH₂ )₃ NH₃ )₂ (CH₃ NH₃ )_n-1 Pb_n I_3n+1 are reported. By using vertically oriented thin films that facilitate efficient charge injection and transport, efficient electroluminescence with a radiance of 35 W Sr^-1 cm^-2 at 744 nm with an ultralow turn-on voltage of 1 V is obtained. Finally, operational stability tests suggest that phase purity is strongly correlated to stability. Phase-pure 2D perovskites exhibit >14 h of stable operation at peak operating conditions with no droop at current densities of several Amperes cm^-2 in comparison to mixtures of 2D/3D or 3D perovskites, which degrade within minutes.