Local lattice softening in semiconductor quantum dots for efficient white light-emitting diodes

White light-emitting diodes based on single-component quantum dots (sc-WQLEDs) have gained great attention owing to their low operating voltage and the high spectral stability of their emission. However, their performance presently lags far behind that of state-of-the-art white organic LEDs owing to a lack of efficient white quantum dot emitters. Creating self-trapped excitons in semiconductor quantum dots is a promising approach to producing broadband white emission. However, such emitters generally suffer from poor charge transport and structural instability. Here we accomplish controllable synthesis of core/shell structured ZnSe/ZnS quantum dots with efficient white emission through combining a sharp excitonic blue emission with a broadband yellow self-trapped exciton emission owing to local lattice softening of ZnSe cores by heterovalent doping with halogen ions. We reveal that the self-trapped excitons confined in the surrounding ZnSe covalent-bond matrix can generate strong and stable yellow emission with minimal reduction of the excitonic blue emission and charge transport capability of ZnSe. On the basis of this approach, we demonstrate highly efficient, heavy-metal-free WQLEDs with a maximum external quantum efficiency up to 15% (average 10.5 +/- 2.6%), a luminance of over 26,000 cd m-2 as well as exceptional device operational lifetime with T50 exceeding 2,500 h at an initial luminance of 100 cd m-2.