Energy Transfer between Inorganic Perovskite Nanocrystals

Cesium lead halide nanocrystals are a new attractive material for optoelectronic applications since they combine the advantageous properties of perovskites and quantum dots. For future applications in optoelectronics and photovoltaics, an efficient energy and/or carrier exchange is a necessary condition. Here, we explicitly demonstrate nonradiative energy transfer for colloidal CsPbBr3 nanocrystals. Using time-resolved optical characterization of purposefully prepared batches of nanocrystals with different sizes, we identify the energy transfer which can be driven by the concentration gradient of excited nanocrystals as well as by the bandgap energy difference. The latter process moves the energy from smaller to larger nanocrystals and opens a possibility of directional streaming of the excitation energy in these materials. The observed energy transfer is enabled in the colloids by proximity of individual nanocrystals due to clustering.