Abstract: The crystalline fraction is a critical parameter for assessing the quality of silicon quantum dots (SiQDs), and its enhancement is anticipated to improve the optoelectronic performance of these materials. However, achieving a high crystalline fraction in small-sized SiQDs produced through the pyrolysis of hydrogen silsesquioxane (HSQ) polymers remains a significant challenge. In this study, we successfully synthesized SiQDs with a diameter of 3.24 nm and a crystalline fraction of 98.4% by optimizing the triethoxysilane (TES)/aqueous hydrochloric acid (HCl) volume ratio during the hydrolysis-condensation process. The SiQDs exhibited a photoluminescence (PL) center at 764.1 nm and an average PL quantum yield (PLQY) of 24.4%. Our findings demonstrate that the TES/aqueous HCl volume ratio significantly influences the proportion of cage structure and the cross-linking density of the network structure in HSQ polymers, which in turn governs SiQD size and crystalline fraction. A high proportion of cage structures in HSQ polymers contributes to high crystallinity. Notably, an increased cross-linking density within the network structure results in higher and more uniform diffusion barriers. This phenomenon not only hinders the diffusion of silicon atoms, which leads to smaller SiQD size, but also facilitates the achievement of high crystalline fraction due to uniform diffusion. This work presents a novel approach to achieving high crystallinity in small SiQDs, with implications for advanced applications in lighting, display technologies, medical imaging, and photovoltaics.

Key words: Silicon quantum dots, Network structure, Cross-linking density, Crystalline fraction, Photoluminescence, HSQ polymers