Lead‐Free, Air‐Stable All‐Inorganic Cesium Bismuth Halide Perovskite Nanocrystals

Abstract

Lead-based perovskite nanocrystals (NCs) have outstanding optical properties and cheap synthesis conferring them a tremendous potential in the field of optoelectronic devices. However, two critical problems are still unresolved and hindering their commercial applications: one is the fact of being lead-based and the other is the poor stability. Lead-free all-inorganic perovskite Cs Bi X (X=Cl, Br, I) NCs are synthesized with emission wavelength ranging from 400 to 560 nm synthesized by a facile room temperature reaction. The ligand-free Cs Bi Br NCs exhibit blue emission with photoluminescence quantum efficiency (PLQE) about 0.2 %. The PLQE can be increased to 4.5 % when extra surfactant (oleic acid) is added during the synthesis processes. This improvement stems from passivation of the fast trapping process (2-20 ps). Notably, the trap states can also be passivated under humid conditions, and the NCs exhibited high stability towards air exposure exceeding 30 days.

Halide Perovskite Nanocrystals for Next‐Generation Optoelectronics

“…However, the toxicity of traditional Pb‐based PNCs is a critical problem that makes this technology still not ready for commercialization . This has recently driven an intense research worldwide toward environmentally friendly and chemically robust Pb‐free perovskite bulk materials, as well as nanocrystals . Nevertheless, the reported Pb‐free PNCs perform still poorly when compared to Pb‐based ones .…”

“…Ternary metal‐halide materials including a trivalent metal ion (bismuth, Bi 3+ ), with similar electronic properties (because of the same 6s2 configuration) as Pb, have A 3 Bi 2 X 9 configuration, e.g., (CH 3 NH 3 ) 3 Bi 2 X 9 or Cs 3 Bi 2 X 9 . Antimony (Sb) is another element with low toxicity, belonging to the same column with Bi in the periodic table.…”

“…Copyright 2016, American Chemical Society. (iii) TR‐PL kinetics of as‐synthesized ligand‐free Cs 3 Bi 2 Br 9 NCs and after being stored in open air for 22 d. Reproduced with permission . Copyright 2017, Wiley‐VCH.…”

Reversible Ultra‐Slow Crystal Growth of Mixed Lead Bismuth Perovskite Nanocrystals: The Presence of Dynamic Capping

“…Further,t hese Pb-based NCs exhibit poor moisture resistance, making these extremelyv ulnerable in the ambient conditions. [10] However,the quantum yield of these Bi-basedp erovskite NCs is very low. [9] Amongt hese, bismuth (Bi)-based perovskites provideabetter stabilityi nt he ambient condition, which is very much required for the application of these materials.…”

“…[10] The reason for the observed crystal growth may be explained by the improper capping of the NCs. This is to note that the FCS studies are done in the nanomolar concentration and the possibility of agglomeration can be ruled out at this low concentration regime, whichs upports the HRTEM data.…”