Metal halide perovskites show promise for light-emitting diodes (LEDs) owing to their facile manufacture and excellent optoelectronic performance, including high color purity and spectral stability, especially in the green region. However, for blue perovskite LEDs, the emission spectrum line width is broadened to over 25 nm by the coexistence of multiple reduceddimensional perovskite domains, and the spectral stability is poor, with an undesirable shift (over 7 nm) toward longer wavelengths under operating conditions, degradation that occurs due to phase separation when mixed halides are employed. Here we demonstrate chloride insertion-immobilization, a strategy that enables blue perovskite LEDs, the first to exhibit narrowband (line width of 18 nm) and spectrally stable (no wavelength shift) performance. We prepare bromide-based perovskites and then employ organic chlorides for dynamic treatment, inserting and in situ immobilizing chlorides to blue-shift and stabilize the emission. We achieve sky-blue LEDs with a record luminance over 5100 cd/m 2 at 489 nm, and an operating half-life of 51 min at 1500 cd/m 2 . By device structure optimization, we further realize an improved EQE of 5.2% at 479 nm and an operating half-life of 90 min at 100 cd/m 2 .
Electro-optic
(EO) modulation is of interest to impart information
onto an optical carrier. Inorganic crystalsmost notably LiNbO3 and BaTiO3exhibit EO modulation and good
stability, but are difficult to integrate with silicon photonic technology.
Solution-processed organic EO materials are readily integrated but
suffer from thermal degradation at the temperatures required in operating
conditions for accelerated reliability studies. Hybrid organic–inorganic
metal halide perovskites have the potential to overcome these limitations;
however, these have so far relied on heavy metals such as lead and
cadmium. Here, we report linear EO modulation using metal-free perovskites,
which maintain the crystalline features of the inorganic EO materials
and incorporate the flexible functionality of organic EO chromophores.
We find that, by introducing a deficiency of cations, we reduce the
symmetry in the perovskite crystal and produce thereby an increased
EO response. The best-engineered perovskites reported herein showcase
an EO coefficient of 14 pm V–1 at a modulation frequency
of 80 kHz, an order of magnitude higher than in the nondefective materials.
We observe split peaks in the X-ray diffraction and neutron diffraction
patterns of the defective sample, indicating that the crystalline
structure has been distorted and the symmetry reduced. Density functional
theory (DFT) studies link this decreased symmetry to NH4
+ deficiencies. This demonstration of EO from metal-free
perovskites highlights their potential in next-generation optical
information transmission.
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