Strategies to Improve Luminescence Efficiency of Metal‐Halide Perovskites and Light‐Emitting Diodes

Abstract

emitters (FWHM ≈ 30 nm; color gamut ≈100% in NTSC standard and <90% in Rec. 2020 standard). [11][12][13][14][15] MHPs are composed of three atoms or molecules in simple crystal structures, ABX 3 or A 2 BX 4 , where A is an organic ammonium (OA, 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., Au 2+ , Sn 2+ , Mn 2+ , and Pb 2+ ), and X is a halide anion (I − , Br − , and Cl − ). In 3D ABX 3 cubic crystal structure, one B cation is coordinated to the six halide anions in a corner of BX 6 octahedral con figuration and A is located in the octahe dral voids. Although bandgap formation mechanism of MHP crystals is still under debate, electronic structure of MHP crys tals is mainly contributed by the inor ganic BX 6 octahedra rather than by the A cations; [16][17][18] these studies indicate that emission wavelength λ of MHP emitters can easily be tuned (380 ≤ λ ≤ 1000 nm) by totally or partially replacing B cations or X anions. Perov skite crystal structure is also affected by Asite cations due to hydrogen bonding and vibrational coupling between BX 3 − and A + , so bandgap and concomitant λ of MHPs can be controlled by tuning the Asite cations. [19,20] These emission spectra with high color purity and wide λ tunability do not depend on the size of grains or crystals of MHP emitters when their dimen sion is larger than exciton Bohr diameter D B ; [21,22] this size independent high color purity of MHPs is particularly suited as a vivid natural color emitter in future display technology.Because of their unique crystal structure (e.g., ionic bonding) and bandgap formation mechanism, MHPs have balanced and high charge carrier mobility (e.g., both electron and hole mobility ≈ 1000 cm 2 (V s) −1 in CsPbBr 3 single crystals [23] ) and have comparable energy level to those of organic semiconduc tors. [24] Furthermore, MHP emitters have low material cost and good compatibility with diverse solution processes to synthe size MHP crystals; these are great advantages of MHPs to mass production and commercialization.In the early 1990s, several researchers tried to fabricate the MHP lightemitting diodes (PeLEDs) by using layered MHP emitters as an emitting layer (EML). [25,26] However, MHPs showed low photoluminescence quantum efficiency (PLQE), and yielded bright electroluminescence (EL) only at cryogenic temperature, which may be ascribed to immature MHP crystalli zation processes, ineffective confinement of electrons and holes, Metal-halide perovskites (MHPs) are well suited to be vivid natural color emitters due to their superior optical and electrical properties, such as narrow emission linewidths, easily and widely tunable emission wavelengths, low material cost, and high charge carrier mobility. Since the first development of MHP light-emitting diodes (PeLEDs) in 2014, many researchers have tried to understand the properties of MHP emitters and the limitations to luminescence efficiency (LE) of PeLEDs, and have devoted ...

Two‐Photon Up‐Conversion Photoluminescence Realized through Spatially Extended Gap States in Quasi‐2D Perovskite Films

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large organic ligands with the formula of A 2 A′ n−1 M n X 3n+1 . [13][14][15] Through down-conversion excitation, 2D perovskites have shown efficient light emission in spontaneous [16,17] and stimulated [18,19] regimes. [13][14][15] Through down-conversion excitation, 2D perovskites have shown efficient light emission in spontaneous [16,17] and stimulated [18,19] regimes.

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“…[9][10][11][12] Such 2D perovskites can demonstrate remarkable tunabilities on optical properties via controlling morphological structures by selecting different functional A/A′ molecules. [13][14][15] Through down-conversion excitation, 2D perovskites have shown efficient light emission in spontaneous [16,17] and stimulated [18,19] regimes. Recently, amplified spontaneous emission (ASE) have been reported in 2D perovskites [(NMA) 2 (FA)Pb 2 Br 7 and (NMA) 2 (FA)Pb 2 Br 1 I 6 ] with stoichiometrically tunable wavelength from visible to near-infrared spectral range (530-810 nm) with the gain coefficient as high as > 300 cm −1 under pulse laser excitation.…”

Exploiting Two‐Step Processed Mixed 2D/3D Perovskites for Bright Green Light Emitting Diodes

“…This suggests a reduced nonradiative recombination in the mixed 2D/3D films, which could be a result from the passivation effects of the large cations as well as the energy funneling process from 2D phases to 3D phases. [6,27,47] To demonstrate the potential of the mixed 2D/3D perovskite film from this two-step method, PeLED with a bottom hole-injecting layer of poly[bis(4-phenyl)(4-butylphenyl) amine] (poly-TPD) on ITO and a top electron-injecting layer of 2′,2′-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)) (TPBi)/LiF/Al were made. The full device structure is shown by the schematic in Figure 3b and the cross-sectional SEM image in www.advopticalmat.de Figure S4 (Supporting Information).…”

Monochromatic LEDs based on perovskite quantum dots: Opportunities and challenges

“…Especially, colloidal perovskite crystals with a size range of a few nanometers or nanocrystals (NCs) have attracted the attention of many scientists because of the quantum‐confined behavior and their unique optical diversity. Several review papers and perspective articles discussing the synthesis and the optical and electronic properties for the integration of perovskite nanocrystals into optoelectronic applications such as photovoltaic applications (solar cells) or light‐emitting devices (LEDs) have been published in the last years …”

“…Several review papers and perspective articles discussing the synthesis and the optical and electronic properties for the integration of perovskite nanocrystals into optoelectronic applications such as photovoltaic applications (solar cells) or light-emitting devices (LEDs) have been published in the last years. [11][12][13][14][15][16][17][18][19][20][21][22] 2 | STRUCTURE, SYNTHESIS, AND REC. 2020…”