Ligand Engineering Achieves Suppression of Temperature Quenching in Pure Green Perovskite Nanocrystals for Efficient and Thermostable Electroluminescence

Abstract

Formamidinium lead bromide (FAPbBr3) perovskite nanocrystals (NCs) are promising for display and lighting due to their ultra-pure green emission. However, the thermal quenching will exacerbate their performance degradation in practical applications, which is a common issue for halide perovskites. Here, we reported the heat-resistant FAPbBr3 NCs prepared by a ligand-engineered room-temperature synthesis strategy. An aromatic amine, specifically β-phenylethylamine (PEA) or 3-fluorophenylethylamine (3-F-PEA), was incorporated as the short-chain ligand to expedite the crystallization rate and control the size distribution of FAPbBr3 NCs. Employing this ligand engineering approach, we synthesized high quality FAPbBr3 NCs with uniform grain size and reduced long-chain alkyl ligands, resulting in substantially suppressed thermal quenching and enhanced carrier transportation in the perovskite NCs films. Most notably, more than 90% of the room temperature PL intensity in the 3-F-PEA modified FAPbBr3 NCs film was preserved at 380 K. Consequently, we fabricated ultra-pure green EL devices with a room temperature external quantum efficiency (EQE) as high as 21.9% at the luminance of above 1,000 cd m−2, and demonstrated less than 10% loss in EQE at 343 K. This study introduces a novel room temperature method to synthesize efficient FAPbBr3 NCs with exceptional thermal stability, paving the way for advanced optoelectronic device applications.

1. Introduction

Lead halide perovskite nanocrystals (NCs) have emerged as a promising class of semiconductor materials for light-emitting applications, owing to their easily tunable optical bandgaps for wide color gamut, narrow emission spectra for excellent color purity, and strong quantum confinement for high photoluminescence quantum yields (PLQYs) [1–6]. The development of perovskite light-emitting diodes (PeLEDs) with perovskite NCs as the emissive layers (EMLs) has been notably swift. Impressively, the external quantum efficiency (EQE) of the blue, green and red PeLEDs based on perovskite NCs have successfully surpassed 20% [7–11], rivaling the performance of other solution processed light-emitting diodes (LEDs) [12–15]. In contrast to traditional inorganic semiconductor NCs such as CdSe [16–18] and InP [19–21], which necessitate high-temperature synthesis in an inert gas atmosphere, perovskite NCs can be synthesized in large quantities by cost-effective methods at room temperature, even under ambient air without the protection of inert gas [22–25].

Despite notable advancements in perovskite NCs, they still suffer from the thermal quenching of luminescence, which probably attributed to the thermal destruction of crystal lattice and non-radiative recombination aided by thermal effects [26, 27]. Addressing the issue of thermal quenching in the soft ionic semiconductors of perovskites remains a big challenge. Among the perovskite NCs, all-inorganic CsPbX3 NCs have garnered significant attention for their decent thermal stability, particularly compared to their organic–inorganic perovskite counterparts [28–32]. Liu et al. have made a significant breakthrough in suppressing thermal quenching effect in the CsPbBr3 NCs which synthesized by a hot injection method with a fluoride post-treatment, enabling a nearly temperature-independent emission efficiency in the range of room temperature to 373 K [33]. Impressively, they demonstrated that a peak EQE of 19.3% at 303 K was achieved in the PeLEDs based on fluoride-treated CsPbBr3 NCs, and the efficiency only dropped by 23% at 343 K. However, the emission peak of CsPbBr3 NCs typically falls below 520 nm [33–35], which restricts their ability to produce the green primary color as defined by the Rec. 2020 standard. In contrast, the FAPbBr3 NCs are proficient at sustaining...