Van der Waals integrated single-junction light-emitting diodes exceeding 10% quantum efficiency at room temperature

The construction of miniaturized light-emitting diodes (LEDs) with high external quantum efficiency (EQE) at room temperature remains a challenge for on-chip optoelectronics. Here, we demonstrate microsized LEDs fabricated by a dry-transfer van der Waals (vdW) integration method using typical layered Ruddlesden-Popper perovskites (RPPs). A single-crystalline layered RPP nanoflake is used as the active layer and sandwiched between two few-layer graphene contacts, forming van der Waals LEDs (vdWLEDs). Strong electroluminescence (EL) emission with a low turn-on current density of ~20 pA μm^-2 and high EQE exceeding 10% is observed at room temperature, which sets the benchmark for the EQE of vdWLEDs ever recorded. Such efficient EL emission is attributed to the inherent multiple quantum well structure and high photoluminescence quantum yield (~35%) of RPPs and a low charge injection barrier of ~0.10 eV facilitated by the Fowler-Nordheim tunneling mechanism. These findings promise a scalable pathway for accessing high-performance miniaturized light sources for on-chip optical optoelectronics.