Metal halide perovskite quantum dots (QDs) recently have attracted great research attentions. However, blue-emitting perovskite QDs generally suffer from low photoluminescence quantum yield (PLQY) because of easily formed defects and insufficient surface passivation. Replacement of lead with low toxicity elements is also preferred toward potential commercial applications. Here, we apply Cl-passivation to boost the PLQY of MA3Bi2Br9 QDs to 54.1% at the wavelength of 422 nm, a new PLQY record for blue emissive, lead-free perovskite QDs. Because of the incompatible crystal structures between MA3Bi2Br9 and MA3Bi2Cl9 and the careful kinetic control during the synthesis, Cl– anions are engineered to mainly locate on the surface of QDs acting as passivating ligands, which effectively suppress surface defects and enhance the PLQY. Our results highlight the potential of MA3Bi2Br9 QDs for applications of phosphors, scintillators, and light-emitting diodes.
Colloidal ZnO nanoparticles (NPs) are widely used as an electron-transporting layer (ETL) in the solution-processed quantum-dot light-emitting diodes (QD-LEDs). However, the inherent drawbacks including surface defect sites and unbalanced charge injection prevent the device from realizing their further performance enhancement. In this work, a series of Mg doped ZnO (ZnO:Mg) and chloride-passivated ZnO (Cl@ZnO) NPs were synthesized by using a solution-precipitation strategy, and they exhibited tunable optical bandgaps and upward-shift of conduction-band maximum (CBM). Solution-processed QD-LEDs based on cadmium-free Cu-In-Zn-S/ZnS (CIZS/ZnS) nanocrystals (NCs) were fabricated by using ZnO:Mg and Cl@ZnO NPs as the ETLs, whose maximum peak external quantum efficiency (EQE) was nearly twice as high as that of QD-LEDs using ZnO NPs as the ETL (EQE = 1.54%). To take advantage of the benefits of ZnO:Mg and Cl@ZnO NPs, Cl@ZnO:Mg NPs were developed through the integration of Mg doping and Cl-passivation. Surprisingly, the cadmium-free QD-LEDs with the Cl@ZnO:Mg NPs as the ETL exhibited a maximum peak EQE of 3.72% and current efficiency of 11.08 cd A–1, which could be enhanced to be 4.05% and 12.17 cd A–1 by optimizing the Cl amount, respectively. The positive effects of the Mg doping and Cl-passivation on the cadmium-free QD-LEDs are primarily ascribed to the reduced electron injection barrier of ETL/the emitting layer interface and slower electron mobility, which can be verified by the ultraviolet photoelectron spectroscopy (UPS) measurements and current density–voltage characteristics of electron-only devices.
PbSe quantum dots (QDs) have shown outstanding optoelectronic properties due to their extremely strong quantum confinement. However, the applications of PbSe QDs are substantially limited by their instability in air. Here, we developed a simple synthesis for PbSe QDs via in situ tuning the reactivity of selenium precursor. Because of in situ chloride passivation, the as prepared PbSe QDs showed excellent stability in air, demonstrated by the retention of absorption features and photoluminescence quantum yields (PL QYs) for different sizes after heated at 80 °C in air. Furthermore, the ligand exchanged electronic coupled PbSe QD thin films also had excellent stability in air even for large particle sizes. In addition, the PbSe QDs showed high PL QYs due to hybrid organic (oleate) and inorganic (Cl–) passivation. Monodispersive large (1st exciton peak > 2100 nm) and extremely small (1st exciton peak < 750 nm) PbSe QDs were achieved by careful control of particle growth. As a heating up method, this new synthesis was easily scaled up to produce 23.5 g PbSe QDs from one batch of reaction. The versatility of this new synthetic strategy was demonstrated by the synthesis of other metal selenide QDs such as CdSe and ZnSe QDs.
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