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.