High-Quality CsPbX₃ (X = Cl, Br, or I) Perovskite Nanocrystals Using Ascorbic Acid Post-Treatment: Implications for Light-Emitting Applications

Abstract

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.

Spray-driven halide exchange in solid-state CsPbX3 nanocrystal films

“…Interestingly, 31 P NMR reveals that TOP is oxidized to trioctylphosphine oxide (TOPO) when I 3 − is reduced to I − (see Fig. S10 in ESI †) [50][51][52][53] TOPO is a well-known capping agent able to stabilize CsPbX 3 NCs and improve their PL properties. The presence of TOPO after the halide exchange is confirmed by 1 x NCs decreases dramatically without TOP.…”

“…These results reveal a PLQY noticeably higher than the initial value for pure CsPbBr 3 NCs, which can be attributed to two reasons: (1) at large sprayed volumes, the amount of TOPO molecules is now enough to passivate surface defects. [50][51][52][53] (2) Surface passivation promoted by surface passivation promoted by the excess of I − in the mixed halide PNCs, 35,45 as Br vacancies in CsPbBr 3 NCs have been reported to act as trapping states leading to a fast non-radiative decay pathway. 46,47 With further sprayed volumes, the PL peak wavelength continues to shift towards the red, 646, and 666 nm, but PLQY decreases to 70% and 60% for 6 and 7 mL of HI, respectively.…”

Year-Long Stability and Near-Unity Photoluminescence Quantum Yield of CsPbBr3 Perovskite Nanocrystals by Benzoic Acid Post-treatment

“…Many researchers demonstrate that it gives rise to complex multiexponential PL decay kinetics. , To date, many reports show the improvement of photoluminescence and stability of CsPbX 3 PNCs using simple surface treatment approaches. Many ligands like trioctyl phosphine (TOP), − trioctylphosphine oxide (TOPO), zwitterions, dodecanethiol, octyl phosphonic acid, didodecyl dimethylammonium bromide (DDAB), phthalimide, 3-aminopropyltriethoxysilane (APTES), thiosulfate, thiocyanate, tetrafluoroborate, and ascorbic acid, etc. have been reported so far.…”

Charge Transfer in Photoexcited Cesium–Lead Halide Perovskite Nanocrystals: Review of Materials and Applications

“…Inorganic cesium–lead halide (CsPbX 3 ) perovskite nanocrystals (PNCs) are extremely important in optoelectronic devices, such as light emitters, solar absorber layers, and photocatalysts, because of their light collection and emitting properties. − These PNCs exhibit excellent optical properties such as broad-ranging absorbance, extremely high photoluminescence quantum yield (PLQY; up to near-unity) − with narrow emission and wide spectral tunability, and reduced photoluminescence (PL) blinking . These nanocrystals (NCs) can be synthesized at relatively low temperatures and show tolerance to defects, − long diffusion length, high carrier mobility (∼4500 cm 2 V –1 s –1 ), and low exciton binding energies.…”