Pb deficiency enables the synthesis of CsPbI₃ nanosheets with tunable thickness down to two octahedral layers

CsPbX₃ (X = Cl, Br, I) nanosheets have emerged as a promising platform for tuning quantum confinement effects and achieving efficient optoelectronic devices. However, synthesizing uniform CsPbX₃ nanosheets with monolayer-level thicknesses remains a challenge due to the fast reaction kinetics. Herein, we develop a synthetic strategy that leverages Pb-deficient precursors to control reaction kinetics. Our experimental investigations indicate that Pb deficiency in the precursors decelerates the crystal growth, offering enhanced dimensional control in CsPbX₃ systems. This approach enables the synthesis of uniform CsPbI₃ nanosheets with tunable thickness down to two octahedral layers, which exhibit a narrowband emission at 563 nm and high stability against spectral drift. This method is readily extended to CsPbBr₃ and CsPbCl₃ systems for precise size and shape modulation, thus affording full-color emission tuning within mono-halide perovskites. These findings establish a versatile synthetic strategy poised to advance the design and application of CsPbX₃ nanomaterials and other colloidal nanocrystals.