Colloidal cesium lead halide (CsPbX3) perovskite nanocrystals (PNCs) have been shown to exhibit very bright tunable photoluminescence (PL) in the entire visible range and narrow emission widths with composition control. However, challenges afflict the stability of PNCs, which limits their usage in practical applications. Surface passivation with an additional ligand could be an excellent, easy, and facile approach to enhance the photoluminescence and stability of PNCs. To address the issue of stability, we introduce the abundantly available ascorbic acid as a surface capping ligand to achieve high photoluminescence and stability of CsPbX3 PNCs via post-treatment. Ascorbic acid helps in improving the photoluminescence (PL) quantum yield of all halide variant PNCs, particularly CsPbBr3 and CsPb(Br/I)(3) PNCs. With ascorbic acid post-treatment, the luminescence decay profiles are improved with a significant increase in the PL lifetime. As a proof-of-concept, we recorded PL data of untreated and ascorbic acid-treated PNCs for a considerable amount of time and found that ascorbic acid-capped PNCs exhibit exceptional ambient stability, photostability, and thermal stability. The pure CsPbI3 PNCs, which are thermodynamically unstable at room temperature, become ultrastable in the presence of ascorbic acid, where they showed the preservation of the luminescent phase for 55 d since the date of synthesis when stored in open atmospheric conditions. The ascorbic acid-treated CsPb(Br/I)(3) PNCs also exhibited excellent stability with no trace of halide segregation, unlike the as-synthesized mixed halide perovskites, wherein a blue shift of PL is observed with a significant loss in emission. Stabilizing CsPbX3 PNCs of different halide compositions via a simple surface treatment with ascorbic acid could form the basis for futuristic light-emitting applications.
