High Efficiency Blue and Green Light-Emitting Diodes Using Ruddlesden–Popper Inorganic Mixed Halide Perovskites with Butylammonium Interlayers

Abstract

Ruddlesden–Popper phase inorganic metal halide perovskites are promising candidates for efficient light-emitting diodes (LEDs) with high brightness and color purity. Here, we demonstrate LEDs made from in situ grown CsPbX3 quasi 2D/3D thin films that are color tunable across the entire visible spectrum. CsPbX3 nanosheets are used to produce RP phase perovskites using butylammonium as a separating ligand to create BA2Cs n–1Pb n (Br/Y)3n+1 2D/3D mixed halide thin films, where Y = Cl or I. The number of CsPbBr3 monolayers in these crystals was optimized by changing the butylammonium concentration. We demonstrate a stable perovskite phase with thin emission line widths providing points covering the edge of the CIE triangle and a maximum red/green/blue coverage of ∼130% of the National Television System Committee color standard. Additionally, we are able to report record efficiencies for blue emitting perovskite nanocrystal LEDs with a maximum external quantum efficiency (EQE) of 2.4% and 6.2% at 465 and 487 nm and a maximum luminance of 3340 cd/m2. We also demonstrate efficient green LEDs with a maximum efficiency of 10.1% EQE, 23.3 cd/A and 9.8 lm/W at 16.3 mA/cm2.

Recent advances and prospects toward blue perovskite materials and light‐emitting diodes

“…They served as ligands to limit the further growth in the out‐of‐plane direction, as well as to prevent restacking between individual crystals. Octylammonium bromide (OCTABr), ethylammonium bromide (EABr), butylammonium bromide (BABr), and phenylethylammonium bromide (PEABr) have commonly been used as A‐site ligands to adjust the dimension. By reducing the number of inorganic layers (n), the bandgap of 2D perovskites can be tuned from 2.6 eV (n = 4) to 3.1 eV (n = 1; Figure A) …”

“…A deep valence band (≈ 6.1 eV) in blue emissive perovskites can lead to a large charge injection barrier for blue PeLEDs, and charge carriers can easily be quenched by the PEDOT:PSS interfaces or the ZnO interfaces . In order to reduce the energy barrier, the hole‐injection‐layer (HIL) and the HTL, a common double‐layer structure, were used in Ruddlesden‐Popper inorganic mixed halide perovskites . Adding a layer of PVK on PEDOT:PSS can not only effectively reduce the work function (WF), but can also isolate the interface between the perovskite and PEDOT:PSS, and reduce carrier quenching.…”

“…Over the past few years, LEDs based on metal halide perovskites (MHPs) have shown great potential as candidate in blue-emissive LEDs. 12,[21][22][23][24][25][26][27][28][29] MHPs possess excellent optoelectronic properties, [30][31][32][33][34][35][36][37][38][39] such as narrow emission linewidths (full width at half-maximum [FWHM] < 20 nm), precise tunable bandgaps (ranging from ultraviolet to near-infrared), and high charge carrier mobility and defect tolerance. The ultrahigh color purity and wide color gamut (~150%; the color gamut level for the national television standards committee [NTSC] standard is <100%) grant MHP LEDs great prospects in display applications.…”

Pure Bromide‐Based Perovskite Nanoplatelets for Blue Light‐Emitting Diodes

“…The as‐obtained blue LED exhibited a maximum EQE of 2.12% at a wavelength of 466 nm . Vashishtha et al reported a record EQE value of 6.2% to blue PeLEDs (EL λ = 487 nm), which based on mixed‐halide quasi‐2D BA 2 Cs n −1 Pb n (Br/Cl) 3 n +1 . By changing the butylammonium concentration, PeLEDs with an emission peak at 465 nm also can be achieved.…”

“…The devices were found to be redshift at the bias exceeding 6 V . After 3 years of development, this filed still remains elusive . The best reported EQE result gets stalled at the relative low level ( Table 1 ).…”