Suppression of non-radiative recombination to improve performance of colloidal quantum dot LEDs with a Cs2CO3solution treatment.

We report a 5-fold luminance increase of green-light emitting CdSe@ZnS quantum-dot LEDs (QLEDs) in response to treatment with a 2-ethoxyethanol solution of cesium carbonate (Cs2CO3). The maximum luminous yield of Cs2CO3-treated QLED is as high as 3.41 cd/A at 6.4 V. To elucidate device-performance improvement, we model measured currents as the sum of radiative and non-radiative recombination components, which are respectively represented by modified Shockley equations. Variations in model parameters show that shift in Fermi level, reduction of barrier heights, and passivation of mid-gap defect states are main results of Cs2CO3treatment. In spite of large luminance difference, light-extraction efficiency remains the same at 9% regardless of Cs2CO3treatment because of the similarity in optical structures.