Quantum Yield and Stability Improvement of Two‐Dimensional Perovskite Via a Second Fluorinated Insulator Layer

Aiming at the low luminous‐efficiency of two‐dimensional (2D) perovskite, its quantum yield (QY) and stability are effectively improved by a fluorinated second insulator layer 3,4‐difluoroaniline (F2PA) outside of the first insulator 2‐(2,4‐difluorophenyl) ethylamine (FPEA). The QY of perovskite with two insulator layers is improved by 3.4‐time in contrast with its counterpart with one insulator, which originates from the defect suppression and reduction of exciton Bohr radius by the second layer. The optical stability has extended 1.5‐time by the introduced second layer, as an isolation role for inner decomposed products to volatilize and for outer water molecules to penetrate. The perovskite with two insulator layers retained 90% of its initial optical properties in relative humidity 90%–95% atmosphere for 600 h, meanwhile only 50% for its counterpart with one layer. Two‐more fluorine with stronger hydrophobicity can account for this feature. Adding a second insulator layer is an effective strategy to engineer 2D perovskites and push forward its applications in optoelectronic devices. Fluorinated organic insulators can effectively improve the stability of two‐dimensional perovskites, but decrease their quantum yield. To overcome this problem, a second fluorinated insulator layer is covered via a hydrogen bond. It can suppress defects and reduce exciton Bohr radius, which improves the quantum yield greatly. Besides, the stability can be further improved due to the high fluorine ratio.