Enhancing exciton binding energy and photoluminescence of formamidinium lead bromide by reducing its dimensions to 2D nanoplates for producing efficient light emitting diodes.

Formamidinium lead bromide perovskite nanocrystals (FAPbBr3 PNCs) are extremely promising for applications in green light emitting diodes (LEDs) since their photoluminescence maxima locate in the range of 530-535 nm with a narrow full width at half-maximum (<25 nm). However, the low exciton binding energy (EB) of FAPbBr3 (∼25 meV) hinders its development in LEDs. In this study, we have developed a 2-methyl-1-pentanol assisted hot injection method for the synthesis of 2D FAPbBr3 nanoplates with high stability. Due to strong quantum confinement in two dimensions of the nanoplates, the obtained FAPbBr3 nanoplates exhibited a high EB of 168.4 meV. The high EB dramatically enhances the photoluminescence (PL) properties with a high fluorescence quantum yield of 92%, which realizes a long photoluminescence lifetime of 2 ns with negligible trapping processes. Benefiting from the high EB and outstanding PL properties, the FAPbBr3 nanoplate LED device showed a current efficiency of 17.32 cd A-1 at a low voltage of 4 V, and a corresponding external quantum efficiency (EQE) up to 4.5% with the Commission Internationale de L'Eclairage (CIE) 1931 color coordinates of (0.24, 0.73), providing a new pathway for the fabrication of efficient perovskite based LED devices.