Surface Engineering of Room Temperature-Grown Inorganic Perovskite Quantum Dots for Highly Efficient Inverted Light-Emitting Diodes

Abstract

Inorganic cesium lead bromide quantum dots (CsPbBr 3 QDs) are usually synthesized via a high-temperature process (hot injection, HI). This process is similar to that used for the synthesis of other semiconductor QDs (i.e., CdSe@ZnS), which limits their potential cost advantage. CsPbBr 3 QDs can also be synthesized at room temperature (RT) in a low cost and easily scalable process, which, thus, is one of the greatest advantages of the CsPbBr 3 QDs. However, light-emitting diodes (LEDs) fabricated using RT-QDs exhibit poor performance compared to those of HI-QDs. In fact, QDs are surrounded by insulating ligands to maintain their colloidal stability but these ligands need to be removed to obtain high-performance LEDs. Here, we show that ligand removal techniques used for HI-QDs are not sufficient in the case of RT-QDs. Additional ligand engineering and annealing steps are necessary to remove the excess of ligands from RT-QD films while preventing the coalescence of the QDs. The eventual surface defects induced by annealing can be healed by a subsequent photoactivation step. Moreover, the use of solution processable inorganic charge transport layers can reduce the fabrication costs of LEDs. We fabricated an inverted LED based on a metal oxide electron transport layer and a RT-QD emitting layer which exhibited a maximum current efficiency of 17.61 cd A −1 and a maximum luminance of 22 825 cd m −2 .

Lead Halide Perovskite Nanocrystals: Room Temperature Syntheses toward Commercial Viability

“…The same group expanded their approach soon after, introducing a ligand exchange protocol with didodecyldimethylammonium bromide (DDAB). [67] They demonstrated that DDAB ligands were more resistant to antisolvent washing and annealing, such that oleic acid and oleylamine are mostly removed, while DDAB mostly remained. This hypothesis is illustrated in Figure 4.…”

“…Reproduced with permission. [67] Copyright 2018, American Chemical Society. www.advancedsciencenews.com…”

“…Typically, short esters have been most successful. Depending on the ligand system employed, butyl acetate, [44] ethyl acetate, [35,41,43,[71][72][73][74][75][76][77] mixtures of ethyl and methyl acetate, [78,79] and methyl acetate alone, [67,[80][81][82][83] have been employed. Figure 6 shows a screening study of 36 potential antisolvents, it concurred on the efficacy of short esters, but indicated that diethylene glycol dimethyl ether (diglyme) was the most effective.…”

“…Quaternary ammonium halides have become ubiquitous ligands for CsPbBr 3 NCs, [37,41,44,67,72,[85][86][87] representing an upgrade on the initial amine ligands. Quaternary ammonium halides contain the same binding functionality that a primary amine provides, but are unable to participate in proton exchange.…”

P‐9.2: Role of interlayers in inorganic perovskite thin films LEDs

“…2,3 These properties make them ideal candidates for the next generation of low cost solar cells, PeLEDs, laser, and photosensor. [3][4][5]14,15 Organic perovskites are widely used in laboratories to fabricate high performance devices, however their crystal structure easily degrades at moderate temperature or low relative humidity. Thus, allinorganic PeLEDs are expected to exhibit a higher stability under both storage and operating conditions.…”