Enhancing Light Out-coupling in Perovskite Light-Emitting Diodes through Plasmonic Nanostructures.

Perovskite light-emitting diodes (PeLEDs) have emerged as promising candidates for lighting and display technologies owing to their high photoluminescence quantum efficiency and high carrier mobility. However, the performance of planar PeLEDs is limited by the out-coupling efficiency, predominantly governed by photonic losses at device interfaces. Most notably, the plasmonic loss at the metal electrode interfaces can account for up to 60% of the total loss. Here, we investigate the use of plasmonic nanostructures to improve the light out-coupling in PeLEDs. By integrating these nanostructures with PeLEDs, we have demonstrated an effectively reduced plasmonic loss and enhanced light out-coupling. As a result, the nanostructured PeLEDs exhibit an average 1.5-fold increase in external quantum efficiency and an ∼20-fold improvement in device lifetime. This finding offers a generic approach for enhancing light out-coupling, promising great potential to go beyond existing performance limitations.

Continuous-Wave Lasing in Perovskite LEDs with an Integrated Distributed Feedback Resonator.

Realization of electrically pumped laser diodes based on solution-processed semiconductors is a long-standing challenge. Metal halide perovskites have shown great potential toward this goal due to their excellent optoelectronic properties. Continuous-wave (CW) optically pumped lasing in a real electroluminescent device represents a key step to current-injection laser diodes, but it has not yet been realized. This is mainly due to the challenge of incorporating a resonant cavity into an efficient light-emitting diode (LED) able to sustain intensive carrier injection. Here, CW lasing is reported in an efficient perovskite LED with an integrated distributed feedback resonator, which shows a low lasing threshold of 220 W cm-2 at 110 K. Importantly, the LED works well at a current density of 330 A cm-2 , indicating the carrier injection rate already exceeds the threshold of optically pumping. The results suggest that electrically pumped perovskite laser diodes can be achieved once the Joule heating issue is overcome.

Enhanced Charge Balance for Efficient Electroluminescence from Cesium Copper Halides.

Cesium copper halides have the advantages of high photoluminescence quantum efficiency and good stability, making them attractive for replacing toxic lead halides in the field of perovskite light-emitting diodes (LEDs). However, due to their shallow conduction band and the lack of electron transport layers compatible with it, it remains a great challenge to achieve charge balance in LED devices. This drawback manifests as the accumulation of holes at the interface between the emitting layer and electron transport layer, resulting in nonradiative recombination. Here, we demonstrate an effective approach to address this issue by suppressing hole injection, which is realized through modification of the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) layer with polyethylenimine. This leads to cesium-copper-halide LEDs with a high external quantum efficiency of 5.6%, representing an advance in device architecture for efficient electroluminescence from cesium copper halides.

Efficient and Bright Deep-Red Light-Emitting Diodes based on a Lateral 0D/3D Perovskite Heterostructure.

Bright and efficient deep-red light-emitting diodes (LEDs) are important for applications in medical therapy and biological imaging due to the high penetration of deep-red photons into human tissues. Metal-halide perovskites have potential to achieve bright and efficient electroluminescence due to their favorable optoelectronic properties. However, efficient and bright perovskite-based deep-red LEDs have not been achieved yet, due to either Auger recombination in low-dimensional perovskites or trap-assisted nonradiative recombination in 3D perovskites. Here, a lateral Cs4 PbI6 /FAx Cs1- x PbI3 (0D/3D) heterostructure that can enable efficient deep-red perovskite LEDs at very high brightness is demonstrated. The Cs4 PbI6 can facilitate the growth of low-defect FAx Cs1- x PbI3 , and act as low-refractive-index grids, which can simultaneously reduce nonradiative recombination and enhance light extraction. This device reaches a peak external quantum efficiency of 21.0% at a photon flux of 1.75 × 1021 m-2 s-1 , which is almost two orders of magnitude higher than that of reported high-efficiency deep-red perovskite LEDs. Theses LEDs are suitable for pulse oximeters, showing an error <2% of blood oxygen saturation compared with commercial oximeters.