Abstract:

Quasi-two-dimensional (quasi-2D) perovskites are one of the most promising luminescent layer candidates for light-emitting diodes (LEDs) because of their excellent optoelectronic properties such as large exciton binding energy, efficient energy transfer, high photoluminescence quantum yield, and adjustable band gap. However, the formation of a large number of low-dimensional phases and surface/interface defects during solution processing of quasi-two-dimensional perovskite films gives rise to an increase in non-radiative recombination, resulting in deteriorated light-emitting diode performance. It is highly desirable to simultaneously realize low-dimensional phase formation inhibition and surface/interface defect passivation during quasi-two-dimensional perovskite film formation. Herein, we report a multifunctional additive, 1, 6-bis(acryloyloxy)-2, 2, 3, 3, 4, 4, 5, 5-octafluorohexane (OFHDODA), which has strong physical and chemical interactions with the PEA₂Cs₂Pb₃Br₁₀ precursor that can effectively suppress non-radiative recombination in the perovskite films. The distinct C＝C peak in the Fourier transform infrared spectroscopy (FTIR) spectra and the F 1s peak in the X-ray photoelectron spectroscopy (XPS) spectra showed that OFHDODA molecules were successfully incorporated into the perovskite films, and most OFHDODA molecules existed as monomers. With the addition of OFHDODA, the photoluminescence quantum yield (PLQY) of the perovskite film increased from 19.7% to 49.0%, and the PL emission wavelength red-shifted from 508 to 511 nm. It was demonstrated that hydrogen bond interactions between the polyfluorine structure and PEA⁺ can tune perovskite crystallization dynamics, which inhibit the formation of low-dimensional phases, as shown by the reduced peak intensities at 403 nm (n = 1), 434 nm (n = 2), and 465 nm (n = 3) in the absorption spectra. The strong Lewis base moiety of the ester groups passivates the unsaturated Pb²⁺ defects at the surface and grain boundaries of the perovskite films, as evidenced by the Pb 4f peak shift in the XPS spectra and the C＝O shift in the FTIR spectra. The trap-filled limiting voltage (V_TFL) decreased in both hole-only and electron-only devices, which also proves the reduction of Pb²⁺ defects. At the optimized OFHDODA concentration, the scanning electron microscopy (SEM) and atomic force microscopy (AFM) results from the perovskite films show lower roughness and smoother surface potential, which promotes superior interfacial contact. As a result, perovskite LEDs with a device structure of indium tin oxide glass/poly (9-vinylcarbazole)/perovskite/1, 3, 5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene/8-hydroxyquinolinolato-lithium/Al exhibited an improved maximum external quantum efficiency (EQE) from 8.55% to 13.76%, improved maximum brightness from 16400 to 17620 cd∙m⁻², and increased lifetime from 8 min to 12 min. This process provides an effective way to suppress non-radiative recombination in quasi-2D perovskites via additive molecular structure design, leading to superior electroluminescence performance.

Key words: Quasi-two-dimensional perovskite, Non-radiative recombination, Low-dimensional inhibition, Defect passivation, Polyfluorinated acrylate additive