In Situ Halide Exchange of Cesium Lead Halide Perovskites for Blue Light‐Emitting Diodes

Abstract

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%.

Tuning the energy transfer in Ruddlesden–Popper perovskites phases through isopropylammonium addition – towards efficient blue emitters

“…But for blue-emitting PeLEDs, the progress in efficiency has been lagging behind, although many efforts have been dedicated to improving these devices. 12–25 Recently, a record EQE of 17.9% has been reported by ligand manipulation in on-substrate synthesis of quantum dots. 26…”

“…But for blue-emitting PeLEDs, the progress in efficiency has been lagging behind, although many efforts have been dedicated to improving these devices. [12][13][14][15][16][17][18][19][20][21][22][23][24][25] Recently, a record EQE of 17.9% has been reported by ligand manipulation in on-substrate synthesis of quantum dots. 26 At least three major approaches have been used to fabricate efficient blue-emissive MHP layers with high values of photoluminescence quantum yields (PLQYs), which acts as a primary indicator for a promising emissive layers in emitting devices technology.…”

“…26 At least three major approaches have been used to fabricate efficient blue-emissive MHP layers with high values of photoluminescence quantum yields (PLQYs), which acts as a primary indicator for a promising emissive layers in emitting devices technology. 27 These three approaches rely on the use of active layers of very different nature, namely: (i) 3D MHPs, 15,25,28 (ii) quasi-2D perovskites, 17,21,22,29,30 and (iii) nanocrystals based on 3D MHPs. 16,23,31 The first approach has the advantage of the good charge transport properties of 3D perovskites, which contribute to improve the EQE.…”

“…However, the PLQY is often limited in bulk materials, as it is affected by trap-induced and non-radiative recombination. 25,28 Furthermore, to push the emission towards the blue spectral region, it is common to use Cl/Br mixtures, which are prone to phase separate in Cl-rich or Brrich domains, leading to multiple emission peaks and unstable colour coordinates. 15 In the last strategy, based on perovskites nanocrystals, the colour is primarily tailored by varying the halide composition, although also variation of the dimensionality of the system composing the nanostructure from 3D to 2D perovskites have been reported.…”

Photoluminescence Enhancement for Efficient Mixed‐Halide Blue Perovskite Light‐Emitting Diodes

“…[1] While green, red, and near-infrared PeLEDs have reached external quantum efficiencies (EQEs) over 20%, [2][3][4][5] the EQEs of blue PeLEDs remain moderate. [6][7][8][9][10][11][12][13][14][15] Since blue light is essential in the practical applications of lighting and displays, realizing high-efficiency blue PeLEDs is important and urgent.…”