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Francesco Di Stasio1 Sotirios Christodoulou1 Inigo Ramiro1 Santanu Pradhan1 Yu Bi1 Alexandros Stavrinadis1 Nengjie Huo1 Gerasimos Konstantatos1

1, The Institute of Photonic Sciences - ICFO, Barcelona, , Spain

Metal halide perovskite nanocrystals (NCs)1 are one of the most attractive materials for optoelectronic applications. The most advantageous properties of this class of nanocrystals are their high photoluminescence (PL) quantum yield (PLQY) and color tunability. Very recently, it has been demonstrated that CsPbBr3 NCs can reach near-unity PLQY in solution.2 Yet, retaining the PLQY in film is not trivial, since the NCs are not as well passivated as in solution and close packing can lead to energy-transfer to trap-states and increased self-absorption.
Here, we report a room temperature synthesis of CsPbBr3 NCs with relatively short-ligands (octanoic acid/octylamine) displaying near-unity PLQY in solid state films.3 The synthesis is carried out in air at room temperature via injection of the PbBr2 precursor into a flask containing Cs acetate (instead of the more common Cs+ complexes prepared using Cs2CO3 and a fatty acid) dispersed in a mixture of hexane and 1-propanol. The as-synthesized nanocrystals show a PLQY of 83% in spin-coated films but a facile treatment of the solution employing Pb2+ complexes before spin-coating further enhances the PLQY, which reaches values close to 100%. The high PLQY is further confirmed by the single-exponential decay of the PL (5.8 ns) indicating a nearly complete suppression of non-radiative channels.
Despite the use of relatively short surface ligands in our synthesis, anion exchange with iodide can be carried out at room temperature and in air leading to a high PLQY in film of 65%. Solar cells operating in the wavelength range 350-660 nm can be fabricated in air, and they display a photo-conversion efficiency of 5.3% with an open circuit voltage (Voc) up to 1.31V, among the highest reported for perovskite based solar cells with bandgap below 2 eV.4 Similarly, the pristine nanocrystals (CsPbBr3) have been used in light-emitting diodes whose performance will be here presented and discussed.

References:
(1) Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Krieg, F.; Caputo, R.; Hendon, C. H.; Yang, R. X.; Walsh, A.; Kovalenko, M. V. Nano Lett. 2015, 15 (6), 3692.
(2) Koscher, B. A.; Swabeck, J. K.; Bronstein, N. D.; Alivisatos, A. P. J. Am. Chem. Soc. 2017, 139, 6566−6569.
(3) Di Stasio, F.; Christodoulou, S.; Huo, N.; Konstantatos, G. Chem. Mater. 2017, 29 (18), 7663.
(4) Christodoulou, S.; Di Stasio, F.; Pradhan, S.; Stavrinadis, A.; Konstantatos, G. Submitted

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