In Situ Preparation of Metal Halide Perovskite Nanocrystal Thin Films for Improved Light-Emitting Devices

Abstract

Hybrid organic-inorganic halide perovskite semiconductors are attractive candidates for optoelectronic applications, such as photovoltaics, light-emitting diodes, and lasers. Perovskite nanocrystals are of particular interest, where electrons and holes can be confined spatially, promoting radiative recombination. However, nanocrystalline films based on traditional colloidal nanocrystal synthesis strategies suffer from the use of long insulating ligands, low colloidal nanocrystal concentration, and significant aggregation during film formation. Here, we demonstrate a facile method for preparing perovskite nanocrystal films in situ and that the electroluminescence of light-emitting devices can be enhanced up to 40-fold through this nanocrystal film formation strategy. Briefly, the method involves the use of bulky organoammonium halides as additives to confine crystal growth of perovskites during film formation, achieving CHNHPbI and CHNHPbBr perovskite nanocrystals with an average crystal size of 5.4 ± 0.8 nm and 6.4 ± 1.3 nm, respectively, as confirmed through transmission electron microscopy measurements. Additive-confined perovskite nanocrystals show significantly improved photoluminescence quantum yield and decay lifetime. Finally, we demonstrate highly efficient CHNHPbI red/near-infrared LEDs and CHNHPbBr green LEDs based on this strategy, achieving an external quantum efficiency of 7.9% and 7.0%, respectively, which represent a 40-fold and 23-fold improvement over control devices fabricated without the additives.

In Situ Fabricated Perovskite Nanocrystals: A Revolution in Optical Materials

“…[55,88] Similarly, 3D PNCs of MAPbI 3 and MAPbBr 3 with 5.4 and 6.4 nm in size were also realized at an incorporation molar ratio of 20% with fluorophenylmethylammonium (FPMA) and PEA, respectively (Figure 5b). [89] At higher incorporation amount, however, multilayered RP phases begin to appear with the large OA cations intercalate into the crystal For the excess MABr case, a type I structure was formed with larger bandgap MABr (4.0 eV) and a smaller one for MAPbBr 3 (≈2.2 eV). Reproduced with permission.…”

“…Reproduced with permission. [89] Copyright 2017, American Chemical Society. c) Unit cell structure of quasi-2D (PEA) 2 (MA) n−1 Pb n I 3n+1 perovskites with different 〈n〉 values, showing the evolution of dimensionality from 2D (n = 1) to 3D (n = ∞).…”

“…As mentioned above, the quasi 2D PNC structure can be denoted as L 2 A n−1 B n X 3n+1 . Plenty of investigations have been conducted on the choices of bulky cation L, including PEA, [56,63,64,[89][90][91][92] BA, [55,88,[93][94][95] ethylammonium (EA), [96] phenylmethylamine (PMA), [97] phenylbutylammonium (PBA), [98,99] naphthylmethylamine (NMA) [65,100] and 2-Phenoxyethylamine (POEA). [101] Similar to the pure 2D structure, with the space dimension reduced to nanosized 3D or quasi 2D, the PNCs exhibit strong excitonic behavior.…”

“…[91] In other words, the stability of the quasi 2D PNCs is improved in comparison to the 3D counterparts, which is verified by the device demonstration in many works. [55,89] NCP process was applied in the large OA assisted in situ PNC fabrication in most cases. The boiling point of the selected antisolvent has distinct influences on the final distribution of the multiple quantum wells.…”

Metal Halide Perovskites: Processing, Interfaces, and Light Emitting Devices

“…We show that the reaction and aging kinetics are extremely rapid, complete within 6 s during spin coating. We realize films with roughness on the order of 1 nanometer that consist of nanoscale crystallites, formed by incorporating a bulky organoammonium halide in addition to the stoichiometric 3D perovskite precursors [3,4,5]. These bulky ligands passivate the 3D crystal, lead to considerably enhanced luminescence quantum yields, and increase stability.…”