Calcium-Assisted In Situ Formation of Perovskite Nanocrystals for Luminescent Green and Blue Emitters

Abstract

Organometal halide perovskite nanocrystals show near-unity photoluminescence quantum yield which decrease dramatically in thin films because of nonradiative losses. Here, we demonstrate a solution-processed highly luminescent perovskite film by confining the MAPbBr3 nanocrystals into the inorganic CaBr2 matrix in situ. The confinement of the exciton in small nanograins facilitates radiative recombination. Meanwhile, part of the lattice-incorporated calcium ions could alter the electronic band structures and then increase the exciton binding energy of MAPbBr3 perovskite. The synergism of morphology control and structural regulation leads to efficient radiative recombination and the enhancement of photoluminescence quantum yield from 4.2% to 45.6%. Moreover, the chloride could also be introduced and stabilized into the perovskite lattice through the calcium incorporation. Desirable pure blue (<480 nm) emission was obtained in situ through manipulating the calcium and chloride ions in the precursor solutions without the assistance of bulky ligands. Our strategies of locally creating luminescent color-tunable perovskite films are promising for further improving the performance of organic–inorganic hybrid perovskite electroluminescence devices.

Tunable Green-to-Blue Light Emitting Hybrid Perovskite Nanocrystals: Status Updates and Roadblocks

“…The presence of Ca salts confined charge carriers, passivated grain boundaries and, ultimately stabilized the phase by reorienting NC growth toward the (110) plane, reducing defects and nonradiative recombination. 118 Similarly, Singh et al synthesized Co 2+doped organohalide hybrid perovskite NCs, expressed as CH 3 NH 3 Pb 1−x Co x Br 3−2x Cl 2x . Co 2+ -doped perovskite NCs also showed improved phase stability due to the smaller ionic radius of Co 2+ (70 ppm) compared to Pb 2+ (119 ppm) and better orbital overlap as compared to Ca 2+ , leading to enhanced stability.…”

“…Although B-site substitution has been less explored due to its high formation energy, it has shown the potential to reduce defects and grain boundaries, thereby improving phase stability. Divalent cations, such as Mn 2+ , Ca 2+ , Co 2+ , and Sn 2+ , have been investigated as dopants or substituents at the B-site of the perovskite structure to improve the performance. − …”

“…The PLQY was increased by a factor of 10 (from 4.2% to 45%). The presence of Ca salts confined charge carriers, passivated grain boundaries and, ultimately stabilized the phase by reorienting NC growth toward the (110) plane, reducing defects and nonradiative recombination . Similarly, Singh et al synthesized Co 2+ -doped organohalide hybrid perovskite NCs, expressed as CH 3 NH 3 Pb 1– x Co x Br 3–2 x Cl 2 x .…”

Efficient blue CsPb(Br–Cl)3 nanoparticles enabled by strontium halide and amine halide synergetic optimization

“…In addition, alkali halides such as RbBr, NaBr and KBr have also been successfully introduced to stabilize and improve the blue emission of CsPbX 3 NPs. [25][26][27] More recently, divalent cation doping has been demonstrated to be another approach to tune the optical properties of perovskite NPs. Ni 2+ , Mn 2+ , Sn 2+ , Cd 2+ , Ce 2+ , Cu 2+ , and Zn 2+ have been proven to be able to increase the defect formation energies of perovskites, and thus the PLQYs of these modified perovskite NPs are improved to 40-80%.…”