Room temperature amine-free synthesis of phosphonate-capped CsPbBr3 nanocrystals for LED applications

Brown, Alasdair, Angus Macintyre, Chin, Xin Yu, Hooper, Thomas, Vashishtha, Parth, Bruno, Annalisa, Jamaludin, Nur Fadilah, Pu, Suan-Hui, Jiang, Liudi, Tey, Ju Nie, Damodaran, Bahulayan, Mathews, Nripan and Mhaisalkar, Subodh (2019) Room temperature amine-free synthesis of phosphonate-capped CsPbBr3 nanocrystals for LED applications. 10th International Conference on Materials for Advanced Technologies, Marina Bay Sands, Singapore, Singapore. 23 - 28 Jun 2019.

Abstract

All-inorganic cesium lead bromide (CsPbBr3) perovskite nanocrystals (NCs) have higher thermal stability and lower moisture susceptibility, compared with their organic-inorganic hybrid counterparts. However, the best light-emitting diodes (LEDs) fabricated from pure Cs-based perovskite NCs currently present significantly lower external quantum efficiencies (EQE = 8.7 %) as compared with pure formamidinium lead bromide (FAPbBr3) LEDs (EQE = 13.4 %). This is partially attributable to current purification process for CsPbBr3 NCs, which are typically synthesised by hot-injection using a high concentration of long insulating ligands. However, it has proven challenging to purify NCs effectively to remove excess ligand while retaining a stable, high concentration ink for high-efficiency LED fabrication. Moreover, weakly-bound ammonium ligands resulted from hot-injection processes are also well known source of instability for CsPbBr3 NCs. Thus, improving the synthesis of CsPbBr3 NCs is crucial for the development of more robust perovskite NC LEDs. There are multiple recent studies which demonstrate the strong passivation of CsPbBr3 NCs by phosphonate ligands; However, a simple efficient and highly scalable approach is much needed for future application.

We report the direct room-temperature synthesis of highly luminescent CsPbBr3 NCs capped by phosphonate ligands. The synthesis is amine-free; it helps avoid the substitution of surface cesium for labile ammonium ions, eliminating this source of instability. Our results indicate that phosphonates are an exceptionally promising class of ligands for perovskite NC LED applications. We will also demonstrate that the application of a post-synthetic treatment with didodecyldimethylammonium bromide (DDAB) enables near-unity photoluminescence quantum yield (PLQY). Crucially, high PLQY was obtained for a stable high-concentration dispersion. Thus, coupled with the short ligands employed, this nanocrystal ink shows great promise for LED fabrication.

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Contributors

Author: Alasdair, Angus Macintyre Brown

Author: Suan-Hui Pu

Author: Liudi Jiang

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