Green Electroluminescence Generated by Band-edge Transition in Ag-In-Ga-S/GaSx Core/shell Quantum Dots

Quantum-dot light-emitting diodes (QD-LEDs) that exhibit green emission were fabricated using Ag-In-Ga-S/GaSx (AIGS) core/shell QDs as low-toxicity QDs. Although multi-element QDs such as AIGS are prone to broad-wavelength defect-induced emission, the core/shell structure enables sharp emission from band -edge transitions. The electroluminescence (EL) spectra were found to include a large defect emission component compared with the photoluminescence spectra of the QD films because of the difference in the excitation process of the QDs. The defect emission was attributed to the electrons injected into the emitting layer (EML) being easily trapped at the defect sites in the QDs. The addition of an electron transporting material to the EML effectively blocked the direct injection route and reduced the electron trapping at the defect sites. Consequently, the color purity of the EL emission was enhanced and the QD-LEDs exhibited green EL emission.