Potassium Iodide Doping for Vacancy Substitution and Dangling Bond Repair in InP Core-Shell Quantum Dots

This work highlights the novel approach of incorporating potassium iodide (KI) doping during the synthesis of In_0.53P_0.47 core quantum dots (QDs) to significantly reduce the concentration of vacancies (i.e., In vacancies; V_In^-) within the bulk of the core QD and inhibit the formation of InPO_x at the core QD-Zn_0.6Se_0.4 shell interfaces. The photoluminescence quantum yield (PLQY) of ~97% and full width at half maximum (FWHM) of ~40 nm were achieved for In_0.53P_0.47/Zn_0.6Se_0.4/Zn_0.6Se_0.1S_0.3/Zn_0.5S_0.5 core/multi-shell QDs emitting red light, which is essential for a quantum-dot organic light-emitting diode (QD-OLED) without red, green, and blue crosstalk. KI doping eliminated V_In^- in the core QD bulk by forming K⁺-V_In^- substitutes and effectively inhibited the formation of InPO₄(H₂O)₂ at the core QD-Zn_0.6Se_0.4 shell interface through the passivation of phosphorus (P)-dangling bonds by P-I bonds. The elimination of vacancies in the core QD bulk was evidenced by the decreased relative intensity of non-radiative unpaired electrons, measured by electron spin resonance (ESR). Additionally, the inhibition of InPO₄(H₂O)₂ formation at the core QD and shell interface was confirmed by the absence of the {210} X-ray diffraction (XRD) peak intensity for the core/multi-shell QDs. By finely tuning the doping concentration, the optimal level was achieved, ensuring maximum K-V_In^- substitution, minimal K⁺ and I^- interstitials, and maximum P-dangling bond passivation. This resulted in the smallest core QD diameter distribution and maximized optical properties. Consequently, the maximum PLQY (~97%) and minimum FWHM (~40 nm) were observed at 3% KI doping. Furthermore, the color gamut of a QD-OLED display using R-, G-, and B-QD functional color filters (i.e., ~131.1%@NTSC and ~98.2@Rec.2020) provided a nearly perfect color representation, where red-light-emitting KI-doped QDs were applied.