Super-Efficient Exciton Funneling in Layer-by-Layer Semiconductor Nanocrystal Structures


  • Our results on energy transfer in layer-by-layer assembled semiconductor nanocrystal structures relied on the help of and fruitful discussions with many colleagues. We thank all of them, in particular Dmitry Koktysh, Nikolai Gaponik, Alexey Shavel, Alexander Eychmüller, Stefan Schietinger, Werner Stadler, and Anna Helfrich. Financial support has been provided by the Deutsche Forschungsgemeinschaft through the Gottfried-Wilhelm-Leibniz-Preis.


In semiconductor nanocrystals the electronic energy gap is determined not only by the material but also by the size of the nanocrystals. This allows the construction of an energy-gap gradient normal to multiple layers of nanocrystals where the diameters of the nanocrystals are monotonically increasing or decreasing in subsequent layers. In such devices we observe a highly efficient funneling of excitation energy from layers comprising smaller nanocrystals towards the layer with the largest nanocrystals in the center of the funnel. Most importantly, not only are excitons in radiative states transferred, but also excitons from trapped states, usually lost for luminescence, can be effectively recycled, hence increasing the overall luminescence yield.