Methanol-induced fast CsBr release results in phase-pure CsPbBr 3 perovskite nanoplatelets.

Formation of a non-emissive wide bandgap CsPb 2 Br 5 component often accompanies the synthesis of CsPbBr 3 perovskites, introducing undesired energy states and impeding the charge transport. Here, we demonstrate that a small amount of a methanol additive can promote the CsBr release rate, facilitating CsPbBr 3 formation and suppressing CsPb 2 Br 5 formation. Some of the methanol ionizes into CH 5 O + and CH 3 O - , which act as surface ligands and change the crystallization environment, inducing shape evolution from spherical nanocrystals to rectangular nanoplatelets (NPLs), leading to monodispersed and phase-pure 8 unit-cell-thick CsPbBr 3 NPLs. Meanwhile, nonradiative recombination processes are inhibited as a result of NPL surface passivation. Bright CsPbBr 3 NPLs with a photoluminescence quantum yield reaching 90% were employed as emitters for electroluminescent light-emitting devices.