Bright and Stable Red Perovskite LEDs under High Current Densities.

Perovskite LEDs (PeLEDs) have emerged as a next-generation light-emitting technology. Recent breakthroughs were made in achieving highly stable near-infrared and green PeLEDs. However, the operational lifetimes (T50) of visible PeLEDs under high current densities (>10 mA cm-2) remain unsatisfactory (normally <100 h), limiting the possibilities in solid-state lighting and AR/VR applications. This problem becomes more pronounced for mixed-halide (e.g., red and blue) perovskite emitters in which critical challenges such as halide segregation and spectral instability are present. Here, we demonstrate bright and stable red PeLEDs based on mixed-halide perovskites, showing measured T50 lifetimes of up to ∼357 h at currents of ≥25 mA cm-2, a record for the operational stability of visible PeLEDs under high current densities. The devices produce intense and stable emission with a maximum luminance of 28,870 cd m-2 (radiance: 1584 W sr-1 m-2), which is record-high for red PeLEDs. Key to this demonstration is the introduction of sulfonamide, a dipolar molecular stabilizer that effectively interacts with the ionic species in the perovskite emitters. It suppresses halide segregation and migration into the charge-transport layers, resulting in enhanced stability and brightness of the mixed-halide PeLEDs. These results represent a substantial step toward bright and stable PeLEDs for emerging applications.

Advances in the Application of Perovskite Materials.

Nowadays, the soar of photovoltaic performance of perovskite solar cells has set off a fever in the study of metal halide perovskite materials. The excellent optoelectronic properties and defect tolerance feature allow metal halide perovskite to be employed in a wide variety of applications. This article provides a holistic review over the current progress and future prospects of metal halide perovskite materials in representative promising applications, including traditional optoelectronic devices (solar cells, light-emitting diodes, photodetectors, lasers), and cutting-edge technologies in terms of neuromorphic devices (artificial synapses and memristors) and pressure-induced emission. This review highlights the fundamentals, the current progress and the remaining challenges for each application, aiming to provide a comprehensive overview of the development status and a navigation of future research for metal halide perovskite materials and devices.

Ultralow-voltage operation of light-emitting diodes.

For a light-emitting diode (LED) to generate light, the minimum voltage required is widely considered to be the emitter's bandgap divided by the elementary charge. Here we show for many classes of LEDs, including those based on perovskite, organic, quantum-dot and III-V semiconductors, light emission can be observed at record-low voltages of 36-60% of their bandgaps, exhibiting a large apparent energy gain of 0.6-1.4 eV per photon. For 17 types of LEDs with different modes of charge injection and recombination (dark saturation currents of ~10-39-10-15 mA cm-2), their emission intensity-voltage curves under low voltages show similar behaviours. These observations and their consistency with the diode simulations suggest the ultralow-voltage electroluminescence arises from a universal origin-the radiative recombination of non-thermal-equilibrium band-edge carriers whose populations are determined by the Fermi-Dirac function perturbed by a small external bias. These results indicate the potential of low-voltage LEDs for communications, computational and energy applications.

Tuning Precursor-Amine Interactions for Light-Emitting Lead Bromide Perovskites.

Organic additives with amino moieties are effective in improving the properties of archetypical formamidinium (FA)-based hybrid perovskites for photovoltaic and light-emitting applications. However, a detailed understanding of how amino additives affect the perovskite materials is lacking, impeding developments in this area. Here, by investigating the interactions of lead bromide perovskite precursors with phenethylamine (PEA) and its derivatives with small variations in chemical structure, we reveal that only the secondary amine (N-methyl-2-phenylethylamine (N-PEA)) results in strengthened hydrogen bonds with FABr in precursor solutions, allowing the formation of high-quality perovskite films. The photoluminescence quantum efficiencies (PLQEs) of the resultant perovskite samples on widely used charge-transport substrates are retained to 82% of their original values, indicating reduced sensitivity to interfacial nonradiative traps critical to device applications. Using a standard device structure, green perovskite light-emitting diodes with peak external quantum efficiencies of 12.7% at ∼500 cd m-2 and operational lifetimes (T50) exceeding 10 h (at 100 cd m-2) are obtained.

Germanium-lead perovskite light-emitting diodes.

Reducing environmental impact is a key challenge for perovskite optoelectronics, as most high-performance devices are based on potentially toxic lead-halide perovskites. For photovoltaic solar cells, tin-lead (Sn-Pb) perovskite materials provide a promising solution for reducing toxicity. However, Sn-Pb perovskites typically exhibit low luminescence efficiencies, and are not ideal for light-emitting applications. Here we demonstrate highly luminescent germanium-lead (Ge-Pb) perovskite films with photoluminescence quantum efficiencies (PLQEs) of up to ~71%, showing a considerable relative improvement of ~34% over similarly prepared Ge-free, Pb-based perovskite films. In our initial demonstration of Ge-Pb perovskite LEDs, we achieve external quantum efficiencies (EQEs) of up to ~13.1% at high brightness (~1900 cd m-2), a step forward for reduced-toxicity perovskite LEDs. Our findings offer a new solution for developing eco-friendly light-emitting technologies based on perovskite semiconductors.