Charge carrier localised in zero-dimensional (CH(3)NH(3))(3)Bi(2)I(9) clusters

A metal-organic hybrid perovskite (CH(3)NH(3)PbI(3)) with three-dimensional framework of metal-halide octahedra has been reported as a low-cost, solution-processable absorber for a thin-film solar cell with a power-conversion efficiency over 20%. Low-dimensional layered perovskites with metal halide slabs separated by the insulating organic layers are reported to show higher stability, but the efficiencies of the solar cells are limited by the confinement of excitons. In order to explore the confinement and transport of excitons in zero-dimensional metal–organic hybrid materials, a highly orientated film of (CH(3)NH(3))(3)Bi(2)I(9) with nanometre-sized core clusters of Bi(2)I(9) (3−) surrounded by insulating CH(3)NH(3) (+) was prepared via solution processing. The (CH(3)NH(3))(3)Bi(2)I(9) film shows highly anisotropic photoluminescence emission and excitation due to the large proportion of localised excitons coupled with delocalised excitons from intercluster energy transfer. The abrupt increase in photoluminescence quantum yield at excitation energy above twice band gap could indicate a quantum cutting due to the low dimensionality.