Nanocrystals of Cesium Lead Halide Perovskites (CsPbX₃, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut

Abstract

Metal halides perovskites, such as hybrid organic-inorganic CH3NH3PbI3, are newcomer optoelectronic materials that have attracted enormous attention as solution-deposited absorbing layers in solar cells with power conversion efficiencies reaching 20%. Herein we demonstrate a new avenue for halide perovskites by designing highly luminescent perovskite-based colloidal quantum dot materials. We have synthesized monodisperse colloidal nanocubes (4-15 nm edge lengths) of fully inorganic cesium lead halide perovskites (CsPbX3, X = Cl, Br, and I or mixed halide systems Cl/Br and Br/I) using inexpensive commercial precursors. Through compositional modulations and quantum size-effects, the bandgap energies and emission spectra are readily tunable over the entire visible spectral region of 410-700 nm. The photoluminescence of CsPbX3 nanocrystals is characterized by narrow emission line-widths of 12-42 nm, wide color gamut covering up to 140% of the NTSC color standard, high quantum yields of up to 90%, and radiative lifetimes in the range of 1-29 ns. The compelling combination of enhanced optical properties and chemical robustness makes CsPbX3 nanocrystals appealing for optoelectronic applications, particularly for blue and green spectral regions (410-530 nm), where typical metal chalcogenide-based quantum dots suffer from photodegradation.

Keywords: Perovskites; halides; nanocrystals; optoelectronics; quantum dots.

Figure 1

Monodisperse CsPbX₃ NCs and their structural characterization. (a) Schematic of the cubic perovskite lattice; (b,c) typical transmission electron microscopy (TEM) images of CsPbBr₃ NCs; (d) X-ray diffraction patterns for typical ternary and mixed-halide NCs.

Figure 2

Colloidal perovskite CsPbX₃ NCs (X = Cl, Br, I) exhibit size- and composition-tunable bandgap energies covering the entire visible spectral region with narrow and bright emission: (a) colloidal solutions in toluene under UV lamp (λ = 365 nm); (b) representative PL spectra (λ_exc = 400 nm for all but 350 nm for CsPbCl₃ samples); (c) typical optical absorption and PL spectra; (d) time-resolved PL decays for all samples shown in (c) except CsPbCl₃.

Figure 3

(a) Quantum-size effects in the absorption and emission spectra of 5–12 nm CsPbBr₃ NCs. (b) Experimental versus theoretical (effective mass approximation, EMA) size dependence of the band gap energy.

Figure 4

(a) Emission from CsPbX₃ NCs (black data points) plotted on CEI chromaticity coordinates and compared to most common color standards (LCD TV, dashed white triangle, and NTSC TV, solid white triangle). Radiant Imaging Color Calculator software from Radiant Zemax (http://www.radiantzemax.com) was used to map the colors. (b) Photograph (λ_exc = 365 nm) of highly luminescent CsPbX₃ NCs-PMMA polymer monoliths obtained with Irgacure 819 as photoinitiator for polymerization.