In-Situ Growth of 3D/2D (CsPbBr3/CsPb2Br5) Perovskite Heterojunctions toward Opto-Electronic Devices.

Two-dimensional CsPb2Br5 exhibits intriguing functions in enhancing performance of opto-electronic devices in terms of environmental stability and luminescence properties when composited with other perovskites in different dimensionality. We built a type-I 3D CsPbBr3/2D CsPb2Br5 heterojunction through phase transition where CsPbBr3 QDs in-situ grew into 2D CsPb2Br5. A thorough growth mechanism study in combination with the excited-state dynamic investigations via femtosecond spectroscopy and first-principles calculations, unraveled that the type-I hierarchy enhanced the stability of the heterojunction and spurred its luminous quantum yield through prolonging the lifetime of photogenerated carriers. Mixing the heterojunction with other phosphors encapsulated white LEDs showing a color rendering index of up to 94%. The work thus not only offered one new avenue to build heterojunction by using the "soft crystal" nature of perovskites, but also disentangled the enhanced luminescence mechanism of the heterojunction that can be harnessed for promising applications toward luminescence and display field.