Cost-Effective Ultrabright Silicon Quantum Dots and Highly Efficient LEDs from Low-Carbon Hydrogen Silsesquioxane Polymers
Honoka Ueda, Ken‐ichi Saitow
Abstract
Cost-effective methods of synthesizing bright colloidal silicon quantum dots (SiQDs) for use as heavy-metal-free QDs, which have applications as light sources in biomedicine and displays, are required. We report simple protocols for synthesizing ultrabright colloidal SiQDs and fabricating SiQD LEDs based on hydrogen silsesquioxane (HSQ) polymer synthesis. Red photoluminescence with a quantum yield (PLQY) of 60–80% and LEDs with an external quantum efficiency (EQE) of >10% were obtained at 1/3600th of the cost of existing methods. This was achieved by using HSiCl 3 and a low-polarity solvent to prepare the HSQ polymer and by optimizing the LED hole-injection layer thickness. A stochastic analysis of 31 SiQD syntheses revealed that SiQDs with the highest PLQYs were obtained from a hard, low-carbon HSQ polymer precursor containing many Si–H groups and cage structures. Notably, simple FTIR measurements predicted whether a HSQ polymer would yield high-PLQY SiQDs and high-EQE LEDs. These straightforward, cost-effective protocols should lead to advances in SiQD synthesis and LED fabrication methods.