Quantum Dot Color-Converting Solids Operating Efficiently in the kW/cm² Regime

With rapid progress in the use of colloidal quantum dots (QDs) as light emitters, the next challenge for this field is to achieve high brightness. Unfortunately, Auger recombination militates against high emission efficiency at multiexciton excitation levels. Here, we suppress the Auger-recombination-induced photoluminescence (PL) quantum yield (QY) loss in CdSe/CdS core-shell QDs by reducing the absorption cross section at excitation wavelengths via a thin-shell design. Studies of PL vs shell thickness reveal that thin-shell QDs better retain their QY at high excitation intensities, in stark contrast to thicker-shell QDs. Ultrafast transient absorption spectroscopy confirms increased Auger recombination in thicker-shell QDs under equivalent external excitation intensities. We then further grow a thin ZnS layer on thin-shell QDs to serve as a higher conduction band barrier; this allows for better passivation and exciton confinement, while providing transparency at the excitation wavelength. Finally, we develop an isolating silica matrix that acts as a spacer between dots, greatly reducing interdot energy transfer that is otherwise responsible for PL reduction in QD films. This results in the increase of film PL QY from 20% to 65% at low excitation intensity. The combination of Auger reduction and elimination of energy transfer leads to QD film PL QY in excess of 50% and absolute power conversion efficiency of 28% at excitation powers of 1 kW/cm², the highest ever reported for QDs under intense illumination.