Electrical engineering

Fabrication

Pathology

Nanotechnology

Organic chemistry

Semiconductor

Voltage source

Engineering

Voltage

Halide

Light-emitting diode

Inorganic chemistry

Chemistry

Materials science

Alternative medicine

Layer (electronics)

Phase (matter)

Diode

Electroluminescence

Voltage droop

Optoelectronics

Medicine

Advanced Materials

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 (CH 3 (CH 2 ) 3 NH 3 ) 2 (CH 3 NH 3 ) n −1 Pb n I 3 n +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 &gt;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.

Stable Light‐Emitting Diodes Using Phase‐Pure Ruddlesden–Popper Layered Perovskites