Nikolai Gaponik1 Vladimir Sayevich1 Chris Guhrenz1

1, TU Dresden, Physical Chemistry, Dresden, , Germany

The design of surface ligand shells of nanocrystals (NCs) is of great importance for their applications. Recently, we developed a mild flocculation procedure allowing us to exchange bulky organic NC ligands with short inorganic species, such as halide ions or metal-halide-complexes [1,2]. This kind of ligand exchange is a key step in the NCs design necessary for their applications in solution processable (e.g. printable) electronics. While the all-inorganic ligands provide very short interparticle distances, which is desired for an efficient coupling and charge transfer, their NCs solids outperform organic semiconductors in many critical parameters, such as carrier mobility and chemical stability. Moreover, all-inorganic shells can act as dopants thus ensuring the fine-tuning of the carrier concentration [2].
Nowadays, a variety of successful examples of all-inorganic capping is known. Nevertheless, the formation of 2D or 3D ordered nanostructures from the all-inorganic-capped NCs appears to be extremely challenging. The introducing of a NC hybrid capping by utilizing short-chain amines (e.g. n-butylamine) allows not only an efficient ordering of the NCs, but also extends their processability to common solvents such as chloroform [3]. Finally, the applicability of all-inorganic- and hybrid-capped NCs and their solids for solution processable electronics (e.g. field-effect transistors) is demonstrated.
In addition to applications in electronics, our method can be extended to achieve phase transfer of organically soluble NCs into aqueous media, including biologically relevant buffers. This innovative approach involves the intermediate hybrid ligand capping with e.g. chloride ions and butylamine and the replacement of the short-chain organic compound with functional polyethylene glycols (PEGs). This procedure is quantitative, widely applicable and it significantly preserves original photoluminescence quantum yields of the NCs.
[1] Sayevich, V.; Gaponik, N.; Plötner, M.; Kruszynska, M.; Gemming, T.; Dzhagan, V. M.; Akhavan, S.; Zahn, D. R. T.; Demir, H. V.; Eychmüller, A., Chem. Mater. 2015, 27, 4328.
[2] Sayevich, V.; Guhrenz, C.; Sin, M.; Dzhagan, V. M.; Weiz, A.; Kasemann, D.; Brunner, E.; Ruck, M.; Zahn, D. R. T.; Leo, K.; Gaponik, N.; Eychmüller, A., Adv. Funct. Mater. 2016, 26, 2163.
[3] Sayevich, V.; Guhrenz, C.; Dzhagan, V. M.; Sin, M.; Werheid, M.; Cai, B.; Borchardt, L.; Widmer, J.; Zahn, D. R. T.; Brunner, E.; Lesnyak, V.; Gaponik, N.; Eychmüller, A., ACS Nano 2017, 11, 1559.