Yasser Hassan1 Bo Ram Lee2 Olivia Ashton1 Nakita Noel1 Bernard Wenger1 Richard H. Friend3 Henry Snaith1

1, University of Oxford, Oxford, , United Kingdom
2, Pukyong National University, Nam-Gu, Busan, , Korea (the Republic of)
3, University of Cambridge, Cambridge, , United Kingdom

Metal halide perovskites are promising candidates for use in light emitting diodes (LEDs), due to their potential for colour tuneable and high luminescence efficiency. While recent advances in perovskite based light emitting diodes (PeLEDs) have resulted in external quantum efficiencies (EQEs) exceeding 10% for the green emitters, the EQEs of the red and blue emitters still lag behind. A critical issue to date is creating highly emissive and stable perovskite emitter with the desirable emission band gap to achieve full-colour displays and white LEDs. Herein, we report the preparation and characterization of a stable suspension of cubic CH3NH3PbI3 perovskite nanocrystals (NCs), where we synthesise the NCs via a ligand-assisted re-precipitation technique, using an acetonitrile/methylamine compound solvent system to solvate the ions, and toluene as the anti-solvent to induce crystallisation. Through tuning the ratio of the ligands, the ligand to toluene ratio, and the temperature of the toluene, we obtain a stable solution of CH3NH3PbI3 NCs with a photoluminescence quantum yield exceeding 90%, and tuneable red emission between 660 and 705nm. We demonstrate the utility of these nanocrystals in PeLEDs, resulting in a maximum EQE of 2%.