3D perovskites are promising to achieve efficient and bright deep‐blue light‐emitting diodes (LEDs), which are required for lighting and display applications. However, the efficiency of deep‐blue 3D perovskite‐based LEDs is limited by high density of defects in perovskites, and their deep‐blue emission is not easy to achieve due to the halide phase separation and low solubility of chloride in precursor solutions. Here, an in situ halide exchange method is developed to achieve deep‐blue 3D perovskites by spin‐coating an organic halide salts solution to treat blue 3D perovskites. It is revealed that the halide‐exchange process is mainly determined by halide ion diffusion targeting a concentration equalization, which leads to homogeneous 3D mixed‐halide perovskites. By further introducing multifunctional organic ammonium halide salts into the exchange solution to passivate defects, high‐quality deep‐blue perovskites with reduced trap density can be obtained. This approach leads to efficient deep‐blue perovskite LEDs with a peak external quantum efficiency (EQE) of 4.6% and a luminance of 1680 cd m−2, which show color coordinates of (0.131, 0.055), very close to the Rec. 2020 blue standard. Moreover, the halide exchange method is bidirectional, and blue perovskite LEDs can be achieved with color coordinates of (0.095, 0.160), exhibiting a high EQE of 11.3%.

Chemical passivation via functional additives plays a critical role in achieving high performance perovskite light‐emitting diodes (PeLEDs). Here, perovskite composite films for high performance PeLEDs by using zwitterion 3‐aminopropanesulfonic acid (APS) as the additive are developed. The sulfonic group of APS can simultaneously passivate deep and shallow level defects in perovskites via coordinate and hydrogen bonding, which leads to suppressed non‐radiative recombination and ion migration in the perovskite composite films. Based on this, PeLEDs with a peak external quantum efficiency of 19.2% and a half‐lifetime of 43 h at a constant current density of 100 mA cm−2 are obtained, representing one of the most stable and efficient PeLEDs under high current densities.

Tin‐based perovskites are a promising candidates to replace their toxic lead‐based counterparts in optoelectronic applications, such as light‐emitting diodes (LEDs). However, the development of tin perovskite LEDs is slow due to the challenge of obtaining high‐quality tin perovskite films. Here, a vapor‐assisted spin‐coating method is developed to achieve high‐quality tin perovskites and high‐efficiency LEDs. It is revealed that solvent vapor can lead to in situ recrystallization of tin perovskites during the film‐formation process, thus significantly improving the crystalline quality with reduced defects. An antioxidant additive is further introduced to suppress the oxidation of Sn2+ and increase the photoluminescence quantum efficiency up to ≈30%, which is an approximately fourfold enhancement in comparison with that of the control method. As a result, efficient tin perovskite LEDs are achieved with a peak external quantum efficiency of 5.3%, which is among the highest efficiency of lead‐free perovskite LEDs.

Efficient and stable deep-blue emission from perovskite light-emitting diodes (LEDs) is required for their application in lighting and displays. However, this is difficult to achieve due to the phase segregation issue of mixed halide perovskites and the challenge of synthesizing high-quality single-halide deep-blue perovskite nanocrystals through a traditional method. Here, we show that an antisolvent treatment can facilitate the in situ formation of perovskite nanocrystals using a facile spin-coating method. We find that the dropping time of the antisolvent can significantly affect the constitution of nanocrystal perovskite films. With a delay in the start time of the antisolvent treatment, small single-halide perovskite nanocrystals can be achieved, exhibiting efficient deep-blue emission. The LED device shows a stable electroluminescence (EL) peak at 465 nm, with a peak external quantum efficiency and a peak current efficiency of 2.4% and 2.5 cd A–1, respectively. This work provides a facile approach to changing the size of perovskite nanocrystals, thus effectively tuning their EL emission spectra.

Room‐temperature‐high‐efficiency light‐emitting diodes based on metal halide perovskite FAPbI3 are shown to be able to work perfectly at low temperatures. A peak external quantum efficiency (EQE) of 32.8%, corresponding to an internal quantum efficiency of 100%, is achieved at 45 K. Importantly, the devices show almost no degradation after working at a constant current density of 200 mA m−2 for 330 h. The enhanced EQEs at low temperatures result from the increased photoluminescence quantum efficiencies of the perovskite, which is caused by the increased radiative recombination rate. Spectroscopic and calculation results suggest that the phase transitions of the FAPbI3 play an important role for the enhancement of exciton binding energy, which increases the recombination rate.