Lecithin Capping Ligands Enable Ultrastable Perovskite-Phase CsPbI₃ Quantum Dots for Rec. 2020 Bright-Red Light-Emitting Diodes

Abstract

Bright-red light-emitting diodes (LEDs) with a narrow emission line width that emit between 620 and 635 nm are needed to meet the latest industry color standard for wide color gamut displays, Rec. 2020. CsPbI 3 perovskite quantum dots (QDs) are one of the few known materials that are ideally suited to meet these criteria. Unfortunately, CsPbI 3 perovskite QDs are prone to transform into a non-redemitting phase and are subject to further degradation mechanisms when their luminescence wavelength is tuned to match that of the Rec. 2020 standard. Here, we show that zwitterionic lecithin ligands can stabilize the perovskite phase of CsPbI 3 QDs for long periods in air for at least 6 months compared to a few days for control samples. LEDs fabricated with our ultrastable lecithin-capped CsPbI 3 QDs exhibit an external quantum efficiency (EQE) of 7.1% for electroluminescence centered at 634 nm�a record for all-inorganic perovskite nanocrystals in Rec. 2020 red. Our devices achieve a maximum luminance of 1391 cd/m 2 at 7.5 V, and their operational half-life is 33 min (T 50 ) at 200 cd/m 2 �a 10-fold enhancement compared to control samples. Density functional theory results suggest that the surface strain in CsPbI 3 QDs capped with the conventional ligands, oleic acid and oleylamine, contributes to the instability of the perovskite structural phase. On the other hand, lecithin binding induces virtually no surface strain and shows a stronger binding tendency for the CsPbI 3 surface. Our study highlights the tremendous potential of zwitterionic ligands in stabilizing the perovskite phase and particle size of CsPbI 3 QDs for various optoelectronic applications.

Halide-Driven Halogen–Hydrogen Bonding versus Chelation in Perovskite Nanocrystals: A Concept of Charge Transfer Bridging

“…The recent reports on using zwitterionic molecules, e.g., lecithin, during the postsynthetic process shows enhanced surface adhesion along with precise size and shape control of perovskite NCs and may open a new direction for enhancing the stability of NCs colloids. − While such zwitterionic molecules are promising for enhancement in the surface coupling, they still form an insulating layer around perovskite NCs and therefore may affect the charge transfer properties. In this regard, it is essential to comprehend the nature of surface coupling of such bidentate ligands on the NCs surface. − Stronger surface coupling of these capping ligands may translate to the inherent lattice vibrations of perovskite NCs and may alter the optical properties of the coupled system.…”

Mn4+-Doped Fluoride Nanocrystals Enable High-Resolution Red-Emitting X-ray Imaging Screens

“…The XRD patterns of the films stored for more than 7 months also showed no change in phase composition (Figure S20). These results indicate excellent emission and phase stability of the Mn 4+ -doped NCs over time, which is higher than that of other red-emitting NCs, such as InP and CsPbI 3 QDs. − Moreover, we tested the thermal stability of the NC films by measuring their temperature-dependent PL spectra between 100 and 475 K (Figure S21–S22). The luminescence quenching temperature T 1/2 , defined as the temperature at which the PL intensity reaches half of its initial value (at 300 K), is around 475 K for Cs 2 SiF 6 :Mn 4+ and Cs 2 SnF 6 :Mn 4+ NCs and about 445 K for K 3 AlF 6 :Mn 4+ NCs, which are close to the values derived for the bulk phosphors .…”

Ultra-small α-CsPbI3 perovskite quantum dots with stable, bright and pure red emission for Rec. 2020 display backlights

“…10,33 Recently, Mir et al developed quantum-confined CsPbI 3 perovskite QDs with bright-red emission and a PL emission maximum at 627 nm and a PLQY close to 100% by using zwitterionic lecithin ligands. 34 However, the CsPbI 3 perovskite QDs with high PLQYs can only be maintained in solution. The nearly 100% PLQY of CsPbI 3 QDs in the colloidal phase decreased to 68% for lecithin-stabilized QD films and the PL spectra of the QD films were red-shifted.…”