View article

DOI: 10.1002/adma. 201602897 create mixed-halide perovskites, the emission wavelength can be tuned throughout the entire visible range.[11] Recently, the extension of this perovskite material to nanocrystals (NCs) has led to an improved quantum efficiency of up to 90%, greatly reducing the loss mechanisms prevalent in bulk perovskite films.[12] While in general the NCs displayed bulk-like optical properties, recent reports of NCs showing quantum-confinement have emerged.[11, 13–20] Interestingly, this material shows a propensity for forming thin nanoplatelets (NPls) under the right synthetic conditions, with thicknesses ranging down to a single perovskite unit cell, as demonstrated for the case of CH3NH3PbBr3.[13, 14, 21] Such quantum-confined nanostructures have garnered significant interest since the first report on colloidal CdSe platelets [22] and subsequent reports highlighting fascinating properties such as a giant oscillator strength transition, thickness-dependent exciton binding energies of several hundreds of meV, narrow emission spectra and extremely short radiative decay times.[23–25] The high quality of such NPls has already led to their promising application in light-emitting applications.[26, 27] Despite these initial reports, there is still a need for the development of universal fabrication methods enabling high yield, high quality, and tunability of the emerging perovskite NPls. This pertains especially to perovskites comprising not only bromide, as often reported, but also comprising iodide, chloride, and mixtures of all three. To this end, we have developed a general approach for the fabrication of 2D organic/inorganic halide …