Methanol-Induced Fast CsBr Release Results in Phase-Pure CsPbBr3 Perovskite Nanoplatelets

The non-emissive wide bandgap CsPb2Br5 component often accompany the synthesis of CsPbBr3 perovskites, introducing undesired energy states impeding the charge transport. Here, we demonstrate that a diminutive amount of methanol additive can promote the CsBr release rate, facilitating the CsPbBr3 formation and suppressing the CsPb2Br5 formation. Part of the methanol ionize into CH5O+ and CH3O-, which act as surface ligands and change the crystallization environment, inducing the shape evolution from spherical nanocrystals to rectangular nanoplatelets (NPLs), leading to monodispersed and phase-pure 8 unit-cell-thick CsPbBr3 NPLs. Meanwhile, the nonradiative recombination processes are inhibited as a result of the NPL surface passivation. Bright CsPbBr3 NPLs with the photoluminescence quantum yield reaching 90% were employed as emitters for electroluminescence light-emitting devices.