Long-term ambient air-stable cubic CsPbBr₃perovskite quantum dots using molecular bromine

Abstract

We report unprecedented phase stability of cubic CsPbBr 3 quantum dots in ambient air obtained by using Br 2 as halide precursor. Mechanistic investigation reveals the decisive role of temperaturecontrolled in situ generated, oleylammonium halide species from molecular halogen and amine for the long term stability and emission tunability of CsPbX 3 (X ¼ Br, I) nanocrystals.High photoluminescence quantum yield (PL QY), narrow emission linewidth, tunable band gap, large diffusion lengths and low exciton binding energies are some of the key attributes of all-inorganic caesium lead halide perovskite nanocrystals (LHP NCs) i.e., CsPbX 3 , X ¼ I, Br, This novel class of NCs has been shown to be highly "defect tolerant", i.e. defect states are either shallow or localized in the valence or the conduction band. 1,2 Unlike conventional semiconductor NCs, the rigorous passivation of their surface via formation of core/shell structures or other methods is not required to achieve high QY. These LHP NCs are promising building blocks for light emitting diode, 3,4 solar cell, 5,6 laser, 7 photocatalysis 8 and detector. 9 Despite the recent surge of studies on CsPbX 3 perovskite NCs, a persisting drawback is their poor phase stability in ambient air. For example, cubic (a) "black" phase CsPbI 3 (E g ¼ 1.73 eV) perovskite NCs undergo rapid phase transformation to nonluminescent orthorhombic (d) "yellow" phase in ambient condition ( Fig. S1 †) leading to undesired changes of the band gap, optical and electrical properties. 6,10,11 Similarly, cubic (a) CsPbBr 3 (E g ¼ 2.25 eV) is unstable at ambient condition. 12 For successful integration of these materials into devices, the issue of long-term phase stability must thus be addressed. 6,13 Most of the reported strategies involve the use of additives such as halide salt, 12 phosphinic acid, 14 ammonium halide, 11 2,2 0 -iminodibenzoic acid 15 sulphides and metal ions 16 and polymers 5 or via special post-synthetic purication step. 6,10 Herein, we report the rst synthesis of highly stable, cubic a-CsPbBr 3 perovskite NCs using Br 2 as an independent halide precursor. In a typical synthesis, lead acetate is dissolved in 1-octadecene in the presence of oleyl amine (OAm) and oleic acid (OA). To this solution, Br 2 (warning: handle the liquid Br 2 in fume hood, Br 2 vapors are toxic) and caesium oleate solutions (both dissolved in ODE) are sequentially added. Phase stability and emission colour tunability are achieved by controlling the reaction temperature (75-200 C) and amount of Br 2 (0.6-1.2 mmol) under air-free synthetic condition (cf. ESI; Experimental section †). The "three-precursor" nature 16-18 of our synthetic scheme allows for independent tuning of the amount of the individual elements viz., Cs + , Pb 2+ and X À ions and in turn, allows for the precise control over the surface chemistry. 17 Highly crystalline, monodisperse 7.62 AE 1.0 nm sized cubic a-CsPbBr 3 NCs (Fig. 1a) were synthesised under optimized conditions using Cs : Pb : Br 2 ratio of 1 : 1 : 6 at 200 C. Highresol...

Meeting High Stability and Efficiency in Hybrid Light‐Emitting Diodes Based on SiO2/ZrO2 Coated CsPbBr3 Perovskite Nanocrystals

“…Finally, the XRD patterns of the CsPbBr 3 @SiO 2 /ZrO 2 support the successful formation of cubic CsPbBr 3 perovskite. Figure 1i displays diffraction peaks at around 14.9°, 21.4°, 30.5°, 34.2°, 37.6°, and 43.6° that correspond to the crystal planes of (100), (110), (200), (210), (211), and (300), respectively, characteristic of the cubic CsPbBr 3 phase [ 27 ] —portable document format (PDF) Card No. #54‐0752, green lines.…”

High Efficiency Mesoscopic Solar Cells Using CsPbI3 Perovskite Quantum Dots Enabled by Chemical Interface Engineering

“…[10][11][12][13][14][15][16][17] Importantly, in form of colloidal QDs the structure could effectively retain the black cubic phase of CsPbI 3 (direct band gap of 1.73 eV), which otherwise easily transforms to the thermodynamically stable orthorhombic δ-CsPbI 3 phase (indirect band gap of 2.82 eV) in thin film structure. 10,18 Subsequently, the successful application of this material in planar perovskite solar cells (PSCs) has been demonstrated, reaching very recently PCEs of up to 14.1%, which constitutes the record value reported for QD-based solar cells. 12,[19][20][21][22] To achieve high performances, both the optimization of the photoactive material (the perovskite layer) and of the different interfaces (such as the electron transport material (ETM)/perovskite interface, hole transport material (HTM)/perovskite interface) are important.…”

Halide Perovskite Nanocrystal Photocatalysts for CO2 Reduction: Successes and Challenges

“…The chemical formula of conventional halide perovskite materials can be described as ABX 3 presented in Figure a, where A is a 12-fold coordinated cation that occupies the cuboctahedra cavity and B is a cation with 6-fold coordination with X anions at corner-sharing BX 6 octahedra. − Recently, several high-performing perovskite materials in which A for methylammonium (MA), formamidinium (FA), or Cs; B is Pb, Bi, or Sn; and X is Cl, Br or I were developed. − Besides these conventional perovskite materials, double perovskite, Cs 2 AgBiBr 6 , is also reported as photoacatalysts. , These perovskites have also shown remarkable photo physical, optical, and transport properties, such as long charge carrier lifetimes and low trap densities, long electron and hole diffusion lengths, higher absorption coefficients, and a widely tunable band gap that enables light harvesting in the UV to near IR spectral range (Figure b). ,− More importantly, the band positions of most halide perovskites satisfy the thermodynamic requirements for CO 2 reduction. Figure c presents the schematic presentation of band position as well as band gap of reported halide perovskite materials along with CO 2 reduction potential.…”