Here, we present the cesium lead halide (CsPbX3, X = Cl, Br, and I) based perovskite quantum dots (PeQDs) for applications in light emitting devices (LEDs). The development of perovskite-based photoactive materials for optoelectronics applications, especially in solar cells, LEDs, and lasers, has been widely pursued due to their prominent optoelectronic properties. Recently, these emerging materials have been successfully synthesized in nano-sized regime to investigate their interesting physico-chemical properties such as the quantum confinement effect. The resulting PeQDs exhibited remarkable optical properties including high quantum yield, readily tunable band gap, and high color purity. All inorganic perovskites, like CsPbX3, possess relatively better stability with uniform morphology than organohalide perovskites, MAPbX3 (MA = CH3NH3). However, the surface passivating ligands of CsPbX3 PeQDs are easily torn off from their weak binding strength, resulting in the increased defect level of CsPbX3 PeQDs. To reduce the diffusion rate of surface binding ligands, we propose solid-state ligand exchange (SLE) method with short chain ligands. From SLE, the photoemission properties of PeQDs were improved through the reduction of surface defect mediated non-radiative recombination process. Also, SLE with short chain ligands provided PeQDs coupling from shrinkage of particle to particle distance. For PeQD-based LED fabrication, CsPbX3 PeQDs layer was processed with subsequent hole injection layer and/or metal electrode via thermal evaporator under vacuum condition. The alkyl chain based short chain ligands have lower boiling point than long chain ligands, which induced vaporization of surface passivating ligand under vacuum environment for the short chain passivation condition. To prevent evaporation of ligands under vacuum condition, we compared various carbon numbers of alkyl chain and aromatic benzyl ligand molecules to guarantee the stability under the thermal evaporation process. The PeQD LEDs with SLE treatment showed improved device performance in red (CsPbI3), green (CsPbBr3), and blue (CsPbBr2Cl) emissions. In particular, green emission exhibited approximately 230% and 770% increase in the luminance and current efficiency, respectively.

High performance CsPbX3 perovskite quantum dot light emitting devices achieved via solid-state ligand exchange

253rd National Meeting (2017)

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