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

We report a five-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 (CsCO). The maximum luminous yield of CsCO-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 a shift in Fermi level, reduction of barrier heights, and passivation of mid-gap defect states are the main results of CsCO treatment. In spite of a large luminance difference, light-extraction efficiency remains the same at 9% regardless of CsCO treatment because of the similarity in optical structures.