Solid-State Anion Exchange Reactions for Color Tuning of CsPbX₃ Perovskite Nanocrystals

Abstract

Herein, we report on a room-temperature anion exchange reaction of highly emitting, all-inorganic CsPbBr 3 nanocrystals (NCs) taking place entirely in the solid state. A fast exchange from Br to I and Br to mixed Br/Cl without exertion of additional energy is observed within minutes to hours, taking place by immobilization of the perovskite NCs on pure potassium halide salts (KCl, KBr, and KI). Via adjustment of the halide ratios of the embedding salt matrix, the bright fluorescence of the CsPbX 3 (X = Cl, Br, or I) NCs can be tuned over a wide spectral range (400−700 nm) while maintaining the initial photoluminescence quantum yields of ∼80% and narrow full widths at half-maximum. We found that combinations of different initial CsPbX 3 NCs and KX matrices result in different final halogen contents of the NCs. This is explained with a host-lattice limiting exchange mechanism. The anion exchange rate can be accelerated by pressing the soft, NC-loaded salts under pressure of 2.2 GPa. Because of the "cold flow" behavior of the potassium salts during the pressing, a complete embedding of the NCs into transparent salt pellets is achieved. This strategy allows for an easy adjustment of the NC loading as well as the form and thickness of the resulting composite. An encapsulation of the NC−salt pellets with silicone yields robustness and stability of the embedded NCs under ambient conditions. The ease of handling and the superior stability make the resulting perovskite composite materials attractive for various photonic and optoelectronic applications as demonstrated in a proof-of-concept color-converting layer for a light−emitting diode.

Facile Two‐Step Synthesis of All‐Inorganic Perovskite CsPbX3 (X = Cl, Br, and I) Zeolite‐Y Composite Phosphors for Potential Backlight Display Application

“…[1][2][3] Backlight applications require WLEDs with a wide color gamut, typically achieved using a blue light-emitting diode (LED) chip in combination with narrowband red (R) and green (G) phosphors. [5][6][7][8][9][10][11][12][13] This makes them promising not only as color-conversion phosphors in WLEDs, but also as electroluminescent material in quantum-dot lightemitting diodes, [14][15][16][17] or as gain material in lasers. [5][6][7][8][9][10][11][12][13] This makes them promising not only as color-conversion phosphors in WLEDs, but also as electroluminescent material in quantum-dot lightemitting diodes, [14][15][16][17] or as gain material in lasers.…”

Efficient and Stable CsPb(Br/I)3@Anthracene Composites for White Light-Emitting Devices

“…5,13–17 Moreover, the emission wavelength of perovskite QDs can be easily tuned over the entire visible spectral region by varying halide anions, 18,19 which endows inorganic perovskite QDs with a promising future to be designed as nanophosphors. 16,20 However, the anion-exchange reaction between different halide inorganic perovskites on the other hand limits their application in white light-emitting devices (WLEDs).…”

“…16,20 However, the anion-exchange reaction between different halide inorganic perovskites on the other hand limits their application in white light-emitting devices (WLEDs). 18,19,21,22 …”

Zero-Dimensional Cesium Lead Halides: History, Properties, and Challenges

“…Recently, presynthesized CsPbX 3 NCs were, for instance, embedded in potassium halide salts, and they exhibited high PLQYs and long-term stability, which demonstrates the advantage of embedding LHP NCs in other halide-based salts. 113 Novel synthesis approaches for pure CsX NCs have recently been reported and could aid in designing synthesis routes toward CsBr|CsPbBr 3 composites. 114 Furthermore, devices have so far been limited to Cs 4 PbBr 6 |CsPbBr 3 , and it remains to be seen whether or not other halide-based composites, like Cs 4 PbI 6 |CsPbI 3 , are stable enough to use in devices.…”