Low-Cost Synthesis of Silicon Quantum Dots with Near-Unity Internal Quantum Efficiency.

Jingjian Zhou,Jing Huang,Ilya Sychugov,Archana Samanta,Zhenyu Yang,Jan Linnros,Huai Chen

doi:10.1021/acs.jpclett.1c02187

Abstract

As a cost-effective batch synthesis method, Si quantum dots (QDs) with near-infrared photoluminescence, high quantum yield (>50% in polymer nanocomposite), and near-unity internal quantum efficiency were fabricated from an inexpensive commercial precursor (triethoxysilane, TES), using optimized annealing and etching processes. The optical properties of such QDs are similar to those prepared from state-of-the-art precursors (hydrogen silsesquioxane, HSQ) yet featuring an order of magnitude lower cost. To understand the effect of synthesis parameters on QD optical properties, we conducted a thorough comparison study between common solid precursors: TES, HSQ, and silicon monoxide (SiO), including chemical, structural, and optical characterizations. We found that the structural nonuniformity and abundance of oxide inherent to SiO limited the resultant QD performance, while for TES-derived QDs this drawback can be avoided. The presented low-cost synthetic approach would significantly favor applications requiring high loading of good-quality Si QDs, such as light conversion for photovoltaics.

Highlights

As a cost-effective batch synthesis method, Si quantum dots (QDs) with nearinfrared photoluminescence, high quantum yield (>50% in polymer nanocomposite), and nearunity internal quantum efficiency were fabricated from an inexpensive commercial precursor, using optimized annealing and etching processes
Benefiting from wavelength-tunable photoluminescence (PL),[8−10] high photoluminescence quantum yield (PLQY),[11] and a significant Stokes shift,[12] Si QDs are considered as promising fluorophores in LEDs13,14 and luminescent solar concentrators (LSCs).[15,16]
Si QD-based LEDs have achieved a record external quantum efficiency (EQE) of 6.2%,4 and an optical power efficiency of 7.9% was obtained for an LSC prototype (9 × 9 cm2) based on Si QDs/polymer nanocomposites.[6]

Summary

QD relative priceb

55 ± 6% in OSTE aNote that to estimate mass yields, the mass of Si QDs was evaluated from optical properties (absorption, QY, and emission). bThe relative price of Si QD was calculated based on precursor quotes from different vendors, measured mass losses from annealing, and estimated mass yield of QDs. The oxide on the surface of Si is a known host for charge trap sites, which was well-documented in Si-based nanoelectronics,[55] and was explicitly shown for Si QDs in single-dot lifetime measurements.[56] The IQE and, subsequently, the PLQY are expected to be lower in such a system due to the intermittent trapping and detrapping of carriers, resulting in Auger nonradiative recombinations. Experimental details; XRD spectra of preannealing powders; low-magnification TEM images of Si QDs; TGA analysis; ATR measurements; synthesis optimization from SiO and TES; reproducibility test; PLQY stability test; PLQY dependency on the excitation wavelength; additional PL decays (PDF).

■ ACKNOWLEDGMENTS

Findings

■ REFERENCES