Efficient Quantum Dot Light-Emitting Diodes Based on Trioctylphosphine Oxide-Passivated Organometallic Halide Perovskites

Abstract

Metal halide perovskite quantum dots (QDs) have attracted significant research interest in the next-generation display and solid illumination fields due to their excellent optical properties of high photoluminescence quantum efficiency, high color purity, obvious quantum confinement effect, and large exciton binding energy. A large amount of surface defects and nonradiative recombination induced by these defects are considered as major problems to be resolved urgently for practical applications of perovskite QDs in high-efficiency light-emitting diodes (LEDs). Herein, we report an efficient passivation of green perovskite QD CH₃NH₃PbBr₃ with trioctylphosphine oxide (TOPO). By simply adding the appropriate amount of TOPO into the nonpolar toluene solvent to synthesize CH₃NH₃PbBr₃ QDs, the surface defects of these as-synthesized perovskite QDs are obviously reduced, along with an increased photoluminescence lifetime and suppressed nonradiative recombination. Further investigation indicates that electronegative oxygen from TOPO (Lewis base) bonds with uncoordinated Pb²⁺ ions and labile lead atoms in perovskite. With TOPO passivation, the green perovskite QD LEDs based on CH₃NH₃PbBr₃ show significant performance improvement factors of 93.5, 161.1, and 168.9% for luminance, current efficiency, and external quantum efficiency, respectively, reaching values of 1635 cd m^-2, 5.51 cd A^-1, and 1.64% in the eventual optimized devices. Furthermore, the presence of TOPO dramatically improves stabilities of CH₃NH₃PbBr₃ QDs and related devices. Our work provides a robust platform for the fabrication of low-defect-density perovskite QDs and efficient, stable perovskite QD LEDs.

Figure 1

(a) Schematic illustration of the synthesis process of CH₃NH₃PbBr₃ QDs. (b) Optical photographs of CH₃NH₃PbBr₃ QDs with 0 (control), 50 (TOPO-50), 100 (TOPO-100), and 150 μL (TOPO-150) of TOPO under ambient light and a 365 nm UV lamp.

Figure 2

TEM (left), HRTEM (right top), and corresponding FFT (right bottom) images of CH₃NH₃PbBr₃ QDs with (a) 0, (b) 50, (c) 100, and (d) 150 μL TOPO. Scale bars: 20 and 5 nm. d(200) = 2.96 Å.

Figure 3

(a) TRPL decay curves and (b) steady-state PL spectra of colloidal CH₃NH₃PbBr₃ QDs. Samples were synthesized at RT with a fixed amount of precursors and a varying amount of TOPO in toluene. (c) Fourier transform infrared (FTIR) spectra of TOPO, PbBr₂, and the TOPO-passivated PbBr₂ film.

Figure 4

XPS spectra corresponding to the Pb 4f core-level of CH₃NH₃PbBr₃ QDs with (a) 0, (b) 50, (c) 100, and (d) 150 μL of TOPO.

Figure 5

(a) Schematic illustration of devices with TOPO passivation. (b) Comparison of normalized EL spectra of CH₃NH₃PbBr₃ QD LEDs. The inset is an optical photograph of QD LED_TOPO-100 under 6 V bias. (c) J–V, (d) L–V, (e) CE–V, and (f) EQE–V characteristics of all devices.