Sterically Controlled Synthesis of Amine-Free CsPbBr3 Nanoplatelets for Stable, Pure-Blue Light Emission

Metal halide perovskite nanoplatelets (NPLs) have demonstrated excellent optical properties for light-emitting applications and achieved tunable blue luminescence through thickness control. However, their translation into electronic devices has lagged behind due to poor colloidal and film stability. The main reason for this is the deprotonation of their surface-capped ammonium passivating ligands, resulting in NPL aggregation. Here we report the first facile synthesis of amine-free pure-blue CsPbBr3 NPLs with outstanding thermal and light stability. This is achieved by utilizing an amine-free phosphine oxide route with a surface capping molecule exhibiting large steric hindrance to prevent NPL aggregation. Two-dimensional nuclear magnetic resonance (2D NMR) spectroscopy suggests slower ligand exchange in amine-free NPLs compared to the conventional NPLs, which can be attributed to the strong binding strength of the designated ligand. Consequently, the amine-free NPLs exhibited superior stability against radiation, heat and moisture. We further demonstrate the importance of acid-base equilibrium in this amine-free synthesis route. Through solvent neutralization and passivation with various alkali carbonates, the resulting NPLs attained near-unity photoluminescence quantum yield (PLQY) and pure blue emission.