High-performance tandem perovskite LEDs through interlayer photon recycling

Tandem light-emitting diodes (LEDs), achieved by vertically stacking several units in series to combine the luminance of individual light-emitting elements, are effective for improving efficiency and lifespan compared with single-unit devices^1-3. In particular, tandem perovskite LEDs benefit from the small Stokes shift of perovskites⁴, which-in principle-can enable substantial photon recycling between individual perovskite layers and enhance light extraction from trapped modes. However, a tandem structure that effectively merges the luminance of each perovskite unit still remains a notable challenge. Here we demonstrate efficient and stable tandem LEDs by combining two solution-processed perovskite light-emitting units. This tandem structure effectively combines the original luminance of each light-emitting unit; we argue that the emissions are also substantially enhanced through photon recycling between the individual light-emitting units. Consequently, we achieve tandem perovskite LEDs with a low turn-on voltage of 3.2 V, a high peak external quantum efficiency (EQE) of 45.5% (even 20% higher than the sum of the peak EQEs of single-unit devices), an average peak EQE of 40.9% and a half-lifetime of 64 h at an initial radiance of 70 W sr^-1 m^-2. These findings represent a notable advancement in achieving high-performance and multicolour LEDs through the stacking of perovskite LEDs.