Partial Ligand Stripping from CsPbBr3 Nanocrystals Improves Their Performance in Light-Emitting Diodes

Abstract

Halide perovskite nanocrystals (NCs), specifically CsPbBr₃, have attracted considerable interest due to their remarkable optical properties for optoelectronic devices. To achieve high-efficiency light-emitting diodes (LEDs) based on CsPbBr₃ nanocrystals (NCs), it is crucial to optimize both their photoluminescence quantum yield (PLQY) and carrier transport properties when they are deposited to form films on substrates. While the exchange of native ligands with didodecyl dimethylammonium bromide (DDAB) ligand pairs has been successful in boosting their PLQY, dense DDAB coverage on the surface of NCs should impede carrier transport and limit device efficiency. Following our previous work, here, we use oleyl phosphonic acid (OLPA) as a selective stripping agent to remove a fraction of DDAB from the NC surface and demonstrate that such stripping enhances carrier transport while maintaining a high PLQY. Through systematic optimization of OLPA dosage, we significantly improve the performance of CsPbBr₃ LEDs, achieving a maximum external quantum efficiency (EQE) of 15.1% at 516 nm and a maximum brightness of 5931 cd m^-2. These findings underscore the potential of controlled ligand stripping to enhance the performance of CsPbBr₃ NC-based optoelectronic devices.

Keywords: CsPbBr3; carrier mobility; halide perovskites; light-emitting diodes; nanocrystal films; nanocrystals; surface ligands engineering.

Figure 1

(a) Schematic description of the preparation of the reference CsPbBr₃-DDAB NCs and their subsequent treatment with OLPA. (b) Ultraviolet–visible (UV–vis) absorption and steady-state PL spectra of the various CsPbBr₃ NC suspensions/films (ref: reference sample, OLPA 0: sample washed with only ethyl acetate). (c) PLQY and average PL lifetime values of the NC suspensions (top) and films (bottom). (d) X-ray diffraction patterns of the films. (e) TEM images of the drop-cast suspensions (scale bars are 50 nm).

Figure 2

(a) Device structure of an LED based on CsPbBr₃ NCs (left) and cross-sectional SEM image of the device (right). (b) Band-energy alignment of the adopted device structure. (c) Normalized EL spectra of the six devices when a 4.5 V bias was applied to them. The inset is a representative photograph of OLPA 2 device working at 4.5 V. (d) Current density and luminance versus driving voltage curve of the LEDs. (e) EQE versus current density of the same batch devices. (f) EQE statistics of a series sample.