Cadmium-Free and Efficient Type-II InP/ZnO/ZnS Quantum Dots and Their Application for LEDs
Guncem Ozgun Eren, Sadra Sadeghi, Houman Bahmani Jalali, Maximilian Ritter, Mertcan Han, Işınsu Baylam, Rustamzhon Melikov, Asım Önal, Fatma Oz, Mehmet Şahin, Cleva W. Ow‐Yang, Alphan Sennaroğlu, R. T. Lechner, Sedat Nizamoğlu
Abstract
It is a generally accepted perspective that type-II nanocrystal quantum dots (QDs) have low quantum yield due to the separation of the electron and hole wavefunctions. Recently, high quantum yield levels were reported for cadmium-based type-II QDs. Hence, the quest for finding non-toxic and efficient type-II QDs is continuing. Herein, we demonstrate environmentally benign type-II InP/ZnO/ZnS core/shell/shell QDs that reach a high quantum yield of ∼91%. For this, ZnO layer was grown on core InP QDs by thermal decomposition, which was followed by a ZnS layer via successive ionic layer adsorption. The small-angle X-ray scattering shows that spherical InP core and InP/ZnO core/shell QDs turn into elliptical particles with the growth of the ZnS shell. To conserve the quantum efficiency of QDs in device architectures, InP/ZnO/ZnS QDs were integrated in the liquid state on blue light-emitting diodes (LEDs) as down-converters that led to an external quantum efficiency of 9.4% and a power conversion efficiency of 6.8%, respectively, which is the most efficient QD-LED using type-II QDs. This study pointed out that cadmium-free type-II QDs can reach high efficiency levels, which can stimulate novel forms of devices and nanomaterials for bioimaging, display, and lighting.