Cesium and formamidinium lead bromide perovskite nanocrystals hold great promise for applications as down-converting green phosphors in liquid-crystal displays. In particular, they are unmatched and likely the only kind of emitter for so-called color-filter-free, front-pixel displays [1, 2]. Such pixels must exhibit near complete absorption of the blue backlighting and convert the blue excitation into green photoluminescence with near unity quantum efficiency. Towards these goals, perovskite NCs exhibit a five-fold higher absorption coefficient than their major contenders (InP-based quantum dots). Making such thick films through one-step solution processing, such as ink-jet printing or spin-coating, requires highly concentrated, aggregate-free nanocrystal inks. Using insights from the polymer physics on polymer brushes and our earlier experience with tightly binding zwitterionic capping ligands for perovskite NCs [3], we have identified lecithin as a ligand that is particularly suited for obtaining purified colloids with concentrations as high as 440 mg of NCs per one mL of solvent [4]. This enables the formation of micron-thick, optically smooth and optically clear films through one spin-coating step. At the same time these colloids can be diluted by 8 orders of magnitude, ie. down to 4 ng/mL, without compromising the colloidal and structural integrity of the NCs.

[1] Maksym V. Kovalenko and Maryna I. Bodnarchuk, Chimia, 2017. 71, 461-470.
[2] Haiwei Chen, Juan He, and Shin-Tson Wu, IEEE Journal of Selected Topics in Quantum Electronics, 2017. 23, 1-11
[3] Franziska Krieg, Stefan T. Ochsenbein, Sergii Yakunin, Stephanie ten Brinck, Philipp Aellen, Adrian Süess, Baptiste Clerc, Dominic Guggisberg, Olga Nazarenko, Yevhen Shynkarenko, Sudhir Kumar, Chih-Jen Shih, Ivan Infante and Maksym V. Kovalenko, ACS Energy Letters, 2018, 3, 641-646.
[4] Franziska Krieg et al. submitted