Colloidal Synthesis of Strongly Fluorescent CsPbBr3 Nanowires with Width Tunable down to the Quantum Confinement Regime

Abstract: We report the colloidal synthesis of strongly fluorescent CsPbBr3 perovskite nanowires (NWs) with rectangular section and with tuneable width, from 20 nm (exhibiting no quantum confinement, hence emitting in the green) down to around 3 nm (in the strong quan-tum-confinement regime, emitting in the blue), by introducing in the synthesis a short acid (octanoic acid or hexanoic acid) together with alkyl amines (octylamine and oleylamine). Temperatures below 70 {\deg}C promoted the formation of monodisperse, few unit cell thick NWs that were free from byproducts. The photoluminescence quantum yield of the NW samples went from 12% for non-confined NWs emitting at 524 nm to a maximum of 77% for the 5 nm diameter NWs emitting at 497 nm, down to 30% for the thinnest NWs (diameter ~ 3nm), in the latter sample most likely due to aggregation occurring in solution.

• The paper demonstrates a colloidal synthesis method that precisely controls CsPbBr3 nanowire widths from 20 nm to 3 nm, enabling quantum confinement.
• The study reports enhanced photoluminescence performance, with a quantum yield reaching up to 77% and a blue shift in emission for narrower wires.
• Structural analyses confirm monodisperse, single-crystal nanowires with stable orthorhombic facets, highlighting their potential in advanced optoelectronic applications.

Colloidal Synthesis of Strongly Fluorescent CsPbBr Nanowires with Width Tunable Down to the Quantum Confinement Regime

The paper explores the synthesis of cesium lead bromide (CsPbBr<sub\>3</sub>) nanowires (NWs) with width tunability down to the quantum confinement regime. The focus of this research is on achieving efficient photoluminescence properties through colloidal processing, utilizing short-chain carboxylic acids and alkyl amines. This synthesis approach aims to enhance the performances of NWs in optoelectronic applications, benefiting from both the quantum and classical confinement regimes.

Synthesis Methodology

The authors adopted a colloidal synthesis strategy, introducing short alkyl carboxylic acids (such as octanoic acid and hexanoic acid) in conjunction with alkyl amines. At temperatures below 70°C, they synthesized NWs that display monodisperse characteristics and minimal byproduct formation. As a result, NW widths were precisely controlled between 20 nm (non-confined) and 3 nm (strongly confined). The latter is particularly significant as it involves the quantum confinement regime, demonstrating potential for significant optical and electronic applications.

Photoluminescence and Quantum Yield

This study reports a photoluminescence quantum yield (PLQY) reaching as high as 77% for NWs at a specific width (5 nm diameter), suggesting enhanced radiative recombination efficiency. A remarkable blue shift in the photoluminescence emission was observed as the width decreases, corroborating the quantum confinement effect. The PL peaks shifted from green (524 nm) for broader, less confined NWs, to blue (497 nm and below) for narrower, confined ones.

Morphological and Structural Insights

Through analyses such as BF-TEM and HAADF-STEM imaging, the paper confirms the rectangular section of NWs and characterizes them as single-crystal structures with orthorhombic configurations. Atomic force microscopy further supported these findings, verifying the flat upper surface of the NWs. The authors identify and manipulate specific crystallographic facets to control nanowire growth, emphasizing the critical role of short-chain acids in enhancing facet stability.

Implications and Future Directions

The findings offer promising implications, particularly in enhancing the durability and performance of optoelectronic devices. CsPbBr<sub\>3</sub> NWs, known for their superior resistance to moisture when compared to hybrid counterparts, potentially serve a critical role as active materials in light-emitting diodes, lasers, and photovoltaic cells.

Prospective research should address the instability of the thinnest NWs, advancing synthesis techniques to prevent aggregation and secondary photoluminescence peak formations. Furthermore, understanding the interplay between NW shape and quantum confinement effects could lead to optimizing anion exchange tactics, broadening optical property tunability.

Overall, this research highlights significant advancements in the colloidal synthesis of perovskite NWs, contributing valuable insights to the development of next-generation materials for optoelectronic systems. Continued exploration along these lines is imperative to harness and stabilize the advantageous properties demonstrated by the quantum confinement effects.