Abstract
AbstractQuantum dot‐based light‐emitting diodes (QD‐LEDs) have excellent optical properties; however, their limitations of stability, reproducibility, and scalability due to the solution process are the major drawback. Herein, blue QD‐LEDs fabricated with the conventional vacuum process using an e‐beam‐evaporated TiO2 thin film as an electron transport layer (ETL) are demonstrated. CdZnS/ZnS‐based blue LEDs with a TiO2 thin film are fabricated under ambient conditions. They exhibit maximum external quantum efficiencies of 3.53% and a peak luminance of 2847 cd m−2. These values are retained, which minimizes performance degradation under high potential bias. In addition, the optimized evaporated TiO2 thin film has a negligible red shift (0.5 nm) of the peak wavelength between the photoluminescence spectrum and electroluminescence spectrum with stable full‐width at half‐maximum changing by less than 2 nm at high voltage. Finally, a blue QD‐LED is fabricated on a scalable emission area of 2 × 2 in. with a patterned cathode accompanied by an evaporated TiO2 thin film, which allows to perform conventional photolithography. A highly stable and reproducible vaporized inorganic thin film as the ETL supports the multilayer architecture to minimize the process damage.
Highlights
The interest in semiconductor colloidal quantum dots (QDs) is growing as their tunable bandgaps and functionalized characteristics receive considerable attention for the potential use in various applications such as field-effect transistors, biosensors, solar cells, and lightemitting diodes (LEDs).[1]
Additional insertion of oleic acid (OA) rather than ODE or Tri-n-octylphosphine along with S for the second injection was found to promote high photoluminescence quantum yield (PLQY) and good stability of QDs.[8b]. The consequential QDs were annealed for an hour at 310 °C and cooled down to room temperature under ambient conditions
This featureless nature in the absorption spectrum is not caused by the inhomogeneity of QDs but originates from the alloyed CdZnS core nucleation and the gradient structure due to the diffusion of Zn atoms during the shell growth; the purity required for the QD emission can still be satisfied.[8a]. Further, the PLQY of the CdZnS/ZnS QDs is measured as high as 83% (Figure 2b and Figure S1, Supporting information), which is comparable to the literature report.[8]
Summary
The interest in semiconductor colloidal quantum dots (QDs) is growing as their tunable bandgaps and functionalized characteristics receive considerable attention for the potential use in various applications such as field-effect transistors, biosensors, solar cells, and lightemitting diodes (LEDs).[1]. The optimization results were analyzed to obtain high device performance based on the thickness of the evaporated TiO2 thin films.
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