Enhanced quantum efficiency in mixed donor-acceptor nanocrystal quantum dot monolayers

Colloidal nanocrystal quantum dots have attracted interest for use in light-harvesting and emitting devices. One of the key parameters for such applications is the quantum efficiency. Nanocrystal quantum dots exhibit reduced quantum yield in layers or solids compared with solutions. Optimizing the overall efficiency of the emission is an important goal. Here we report on a large enhancement of the quantum efficiency of mixed TGA-stabilised CdTe quantum dot in closely packed monolayers formed with nanocrystal QDs of two sizes. Energy is transferred from the smaller donor quantum dots to the larger acceptor quantum dots via Förster resonant energy transfer (FRET). The increased quantum efficiency is attributed to exciton recycling from the donor defect states. The acceptor emission enhancement and relative quantum efficiency are strongly dependent on the donor:acceptor concentration ratio. A relative quantum efficiency of 160% is achieved for the mixed quantum dot layer with a donor:acceptor ratio of 11:1.