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

Abstract

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 (E_B) 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 E_B of 168.4 meV. The high E_B 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 E_B 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.