Fine‐Tuning Blue‐Emitting Halide Perovskite Nanocrystals

Abstract Lead halide perovskite nanocrystals (NCs) with narrow, bright emission in the visible range are promising candidates for light‐emitting applications. Near‐unity quantum yields have been realized for green and red‐emitting perovskites, but efficient, stable blue‐emitting perovskite materials are scarce. Current methods to synthesize quantum‐confined CsPbBr₃ NCs with blue emission are limited to specific wavelength ranges and still suffer from inhomogeneously broadened emission profiles. Herein, anisotropic blue‐green emitting CsPbBr₃ NCs are synthesized in ambient atmosphere using a spontaneous crystallization method. Optical spectroscopy reveals a gradual, asymptotic photoluminescence (PL) redshift of pristine colloidal NCs after synthesis. During this process, the emission quality improves notably as the PL spectra become narrower and more symmetric, accompanied by a PL intensity increase. Electron microscopy indicates that the gradual redshift stems from an isotropic growth of the CsPbBr₃ NCs in at least two dimensions, likely due to residual precursor ions in the dispersion. Most importantly, the growth process can be halted at any point by injecting an enhancement solution containing PbBr₂ and organic capping ligands. Thus, excellent control over NC size is achieved, allowing for nanometer‐precise tunability of the respective emission wavelength in the range between 475 and 500 nm, enhancing the functionality of these already impressive NCs.