Perovskite Emitters as a Platform Material for Down‐Conversion Applications

Abstract

for the red, green, and blue (RGB) colors but incorporates white light sources, which can be further converted to RGB emission using color filters (CFs). Recent commercialized televisions and computer monitors generally use down-converted displays (DCDs), in which color conversion phosphor films and CFs are laid atop the blue BLU to change its emission to the desired color. Semiconductor nano particles (NPs) such as cadmium (Cd) quantum dots (QDs) and indium phosphide (InP) QDs with narrow spectral bandwidth, high luminous efficiency, and easy tunable wavelength have been recently introduced as more suitable materials for display application than the yttrium aluminum garnet (YAG) phosphors that are widely used at present. QDs have good color purity, but users demand still higher color purity displays that can represent realistic colors. [1-7] Metal-halide perovskites (shortly, perovskite) have simple crystal structures of ABX 3 or A 2 BX 4 (where A is an organic ammonium (e.g., methylammonium (MA; CH 3 NH 3 +) and formamidinium (FA; CH(NH 2) 2 +)) or an alkali metal cation (e.g., Cs +), B is a transition metal cation (e.g., Pb 2+), and X is a halide anion (I − , Br − , and Cl −) [8] (Figure 1a). Perovskite emitters have higher color purity (color gamut ≥ 140% in National Television Standards Committee (NTSC) TV color standard and ≥95% in International Telecommunication Union (ITU) Recommendation Rec. 2020 standard) than inorganic QDs emitters (full width at half maximum (FWHM) ≈ 30 nm; color gamut ≈ 110-115% in NTSC standard and <90% in Rec. 2020 standard). However, perovskite have low exciton binding energy (≈30-50 meV in MAPbI 3 and ≈76 meV in MAPbBr 3), so most of electron-hole pairs are dissociated into free charge carriers, reducing radiative recombination and photoluminescence quantum yield (PLQY) at room temperature. Perovskite nanoparticles (PeNPs) are highly bright [8] and have unique optical and physical properties such as facile emission wavelength tunability, narrow FWHM, and high PLQY (≥95%) compared to inorganic QDs and organic emitters (Figure 1b) [8] and high absorption coefficient compared to inorganic QDs. Therefore, many researchers have tried to use them as light emitters. However, perovskite emitters have limitations when applied to DCDs. First, polar organic solvents or water cause structural changes in perovskites and consequent loss of optical properties. Second, environmental factors such as moisture, heat, light, and oxygen degrade perovskite emitters. Methods to overcome the instability of perovskites to moisture, light, and heat in down-converted displays (DCDs), in which films of perovskite emitters are placed on top of the backlight unit and convert its light to a desired color, are reviewed here. First, the photophysical properties of perovskite emitters as light converters in DCDs are discussed. Second, five strategies to improve stability of perovskite emitting materials (PeMs) mostly in a form of perovskite nanoparticles (PeNPs) are summarized: i) encapsulation in inorganics, ii)...

Stable Lead-Free Cesium Tin Halide Double-Perovskite Nanocrystals Embedded in Polydimethylsiloxane for Candlelight Light-Emitting Diodes

“…PNCs exhibit poor stability, thereby limiting their broad commercial applications. , The effect between Cs 2 SnBr 6 DPNCs and water/oxygen molecules in the atmosphere can be reduced using PDMS matrix as an ideal protective layer for DPNCs, thereby increasing the stability of DPNCs . In the present study, Cs 2 SnBr 6 DPNCs were embedded in the PDMS matrix to enhance their stability, such as photo- and thermal stability.…”

“…Recently, the luminescence materials of perovskite nanocrystals (PNCs) have been demonstrated to have two types of emission mechanisms; one is narrow-band emission derived from free excitons, and the other is broadband emission from self-trapped excitons (STEs). These types exhibit great advantages for display and lighting applications, respectively. In particular, all-inorganic PNCs are attracting considerable attention in optoelectronics devices because of their wavelength-tunable emission, high photoluminescence quantum yields (PLQYs), narrow full-width at half-maximum (FWHM), and easy fabrication. − PNCs consist of metallic cations (primarily Pb 2+ and Sn 2+ ) and halide anions (primarily Cl – , Br – , and I – ) combined with space-filled cations (primarily Cs + and CH 3 NH 3+ ) .…”

Cesium Manganese Bromide Nanocrystal Sensitizers for Broadband Vis-to-NIR Downshifting

“… 11 , 24 Instead, halide perovskites are ideal for substitutional doping due to the softness and strong ionicity of their lattice, and additionally they offer very high absorption cross sections. 2 , 5 , 25 − 29 Various reports have shown that in lead halide perovskites a downshifted luminescence in the visible and infrared spectral range can be achieved through doping with divalent cations (for instance, Cd 2+ , Mn 2+ ), 30 , 31 trivalent cations (Ln 3+ ), 27 , 32 , 33 or a combination thereof. 28 Yet, the toxicity and stability issues of lead-based perovskites are a strong drive toward alternative metal halides, 34 − 37 and several Pb-free double perovskites (e.g., Cs 2 AgInCl 6 , 38 − 40 Cs 2 AgBiX 6 (X = Cl, Br), 39 , 41 and Cs 3 Bi 2 Br 9 39 ) have been synthesized and tested as hosts.…”

Double Encapsulation of CsPbBr3 Perovskite Nanocrystals with Inorganic Glasses for Robust Color Converters with Wide Color Gamut

“…Similarly, CsPbBr 3 perovskite nanocrystals (PNCs), which have a very narrow emission bandwidth and high quantum efficiency but are susceptible to water, heat, and light, − have been recently developed as perovskite nanocrystals embedded glass (PNEG). − Encapsulating the CsPbBr 3 nanocrystals in inorganic glass matrix improves the stability of the PNCs. PNEG successfully demonstrated its narrow emission bandwidth and high quantum efficiency, along with enhanced stability compared to colloidal CsPbBr 3 nanocrystals. − Ye et al achieved high quantum efficiency, up to ∼80% (under 365 nm excitation) for CsPbBr 3 nanocrystal embedded boro-germanate glass.…”