Designing Efficient Si Quantum Dots and LEDs by Quantifying Ligand Effects
Taisei Ono1, Yuping Xu1, Toshiki Sakata1
1Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
ACS Applied Materials & Interfaces
|December 30, 2021
Summary
This study quantifies factors influencing silicon quantum dot (SiQD) efficiency for light sources. Optimizing ligand coverage and minimizing core stress significantly boosts photoluminescence quantum yield (PLQY) and LED performance.
Area of Science:
- Materials Science
- Nanotechnology
- Optoelectronics
Background:
- Colloidal silicon quantum dots (SiQDs) show promise for next-generation light sources.
- Key factors influencing SiQD efficiency (PL wavelength, PLQY, LED performance) remain unquantified.
- Understanding these factors is crucial for accelerating SiQD design and implementation.
Purpose of the Study:
- To synthesize and characterize colloidal SiQDs with different surface terminations.
- To quantify the impact of ligand type, coverage, stress, and dangling bonds on SiQD photoluminescence quantum yield (PLQY) and LED efficiency.
- To elucidate the relationship between surface chemistry, core stress, and optoelectronic performance.
Main Methods:
- Synthesis of colloidal SiQDs via pyrolysis of hydrogen silsesquioxane.
- Surface termination using 1-decene via thermal (HT-SiQDs) or room-temperature (RT-SiQDs) hydrosilylation.
- Characterization using photoluminescence (PL), PL-excitation, UV-visible absorption, and surface coverage analysis (dangling bonds, Si-H, Si-O-Si, Si-C, Si-Cl).
- Core stress analysis to determine Si-Si bond length changes.
Main Results:
- RT-SiQDs exhibited significantly higher PLQY (54%) compared to HT-SiQDs (19%).
- Surface analysis revealed differences in ligand coverage and dangling bonds between HT-SiQDs and RT-SiQDs.
- Core stress analysis showed a 0.3% Si-Si bond length stretch per ligand termination.
- PLQY and LED efficiency were attributed to low insulator ligand coverage, Cl ligand effects, negligible dangling bonds, and low SiQD core tensile stress.
- RT-SiQDs achieved 80% PLQY in toluene.
- LEDs fabricated with RT-SiQDs showed 20x higher electroluminescence intensity due to differences in current density and Auger recombination.
Conclusions:
- Low coverage of insulating ligands, the influence of Cl ligands on recombination rates, minimal dangling bonds, and low core tensile stress are critical for high SiQD PLQY and LED efficiency.
- The findings provide a quantitative framework for improving SiQD performance.
- These concepts can guide the development of SiQDs with enhanced optoelectronic properties using various ligands.
