Highly Luminescent Violet- and Blue-Emitting Stable Perovskite Nanocrystals

Among the lead halide perovskites, photoluminescence quantum yield (PLQY) of violet-emitting CsPbCl3 nanocrystals (NCs) is the lowest (<5%). This is an impediment to the development of perovskite-based materials for optical applications covering the entire visible region. While PLQY of the green- and red-emitting perovskites of this class has been raised to near-unity, achieving a similar level for violet- and blue-emitting NCs is still quite challenging. Herein, we report a novel method of simultaneously passivating the surface defects and crystal disorder of violet-emitting CsPbCl3 NCs to dramatically enhance (by a factor of similar to 120) the PLQY and stability without affecting the peak wavelength (403 nm) and full-width at half-maximum (FWHM) of the photoluminescence (PL) band. We show that the addition of the correct quantity of CuCl2 during the hot-injection synthesis of CsPbCl3 NCs leads to doping of Cu+ into the NCs, which rectifies octahedral distortion of the crystal and the Cl- passivates the surface; the combined influence of the two results in huge PL enhancement. NCs emitting throughout the blue region (430-460 nm) with near-unity PLQY (92%-98%) can then be obtained by partial halide-exchange of the doped sample. Femtosecond transient absorption studies suggest suppression of the ultrafast carrier trapping process in doped NCs. The results help extending the utility of these materials in optical applications by covering the violet-blue region as well.