Xinyu Shen

Abstract:

The use of a small organic molecular passivator is proven to be a successful strategy for producing higher-performing quasi-2D perovskite light-emitting diodes (PeLEDs). The small organic molecule can passivate defects on the grain surround and surface of perovskite crystal structures, preventing nonradiative recombination and charge trapping. In this study, a new small organic additive called 2, 8-dibromodibenzofuran (diBDF) is reported and examines its effectiveness as a passivating agent in high-performance green quasi-2D PeLEDs. The oxygen atom in diBDF, acting as a Lewis base, forms coordination bonds with uncoordinated Pb²⁺, so enhancing the performance of the device. In addition, the inclusion of diBDF in the quasi-2D perovskite results in a decrease in the abundance of low-n phases, hence facilitating efficient carrier mobility. Consequently, PeLED devices with high efficiency are successfully produced, exhibiting an external quantum efficiency of 19.9% at the emission wavelength of 517 nm and a peak current efficiency of 65.0 cd A-¹.

Abstract:

Surface defects of metal halide perovskite nanocrystals (PNCs) substantially compromise the optoelectronic performances of the materials and devices via undesired charge recombination. However, those defects, mainly the vacancies, are structurally entangled with each other in the PNC lattice, necessitating a delicately designed strategy for effective passivation. Here, a synergistic metal ion doping and surface ligand exchange strategy is proposed to passivate the surface defects of CsPbBr₃ PNCs with various divalent metal (e.g., Cd²⁺, Zn^2+, and Hg²⁺) acetate salts and didodecyldimethylammonium (DDA⁺) via one-step post-treatment. The addition of metal acetate salts to PNCs is demonstrated to suppress the defect formation energy effectively via the ab initio calculations. The developed PNCs not only have near-unity photoluminescence quantum yield and excellent stability but also show luminance of 1175 cd m⁻², current efficiency of 65.48 cd A⁻¹, external quantum efficiency of 20.79%, wavelength of 514 nm in optimized PNC light-emitting diodes with Cd²⁺ passivator and DDA ligand. The “organic–inorganic” hybrid engineering approach is completely general and can be straightforwardly applied to any combination of quaternary ammonium ligands and source of metal, which will be useful in PNC-based optoelectronic devices such as solar cells, photodetectors, and transistors.

Abstract:

Although significant progress has been made in the development of green, red, and near-infrared perovskite light-emitting diodes (PeLEDs), blue PeLEDs exhibit inferior performance, owing to various defects and poor carrier injection in solution-processed perovskite films. Thus, this study incorporates dual-passivation additive diphenylphosphinamide (DPPA) into perovskite films, and through density functional theory calculations and experimental characterizations, DPPA has been proven to be an effective passivator. Its phosphine oxide group coordinates with unsaturated lead ions, passivating perovskite defects, while the amino group forms hydrogen bonds with adjacent halide ions, suppressing their migration and further strengthening the passivation effect. Blue quasi-two-dimensional PeLEDs based on DPPA-modified perovskite films achieved an external quantum efficiency of 12.31% with an emission peak at 486 nm. Moreover, the device operational lifetime was extended by 32% with more stable spectra owing to the decreased defect density and suppressed ion migration in the perovskite film.

Abstract:

Despite the enormous developments in perovskite light-emitting diodes (PeLEDs) recently, obtaining efficient blue PeLEDs is still considered a critical challenge due to the non-radiative recombination and unbalanced charge injection caused by the unmatched carrier mobility and the deep hole-injection barrier between the hole-transport layer (HTL) and the emissive layer (EML). Herein, we incorporate tris(4-trifluoromethylphenyl)phosphine oxide (TMFPPO), obtained through a facile oxidation synthesis process, into poly(9-vinylcarbazole) (PVK). TMFPPO incorporation modulated the energy level and hole mobility of the binary-blend HTLs to eliminate the hole-injection barrier and balance the charge injection within the EML. Consequently, the blue PeLEDs with blended HTL presented an external quantum efficiency (EQE) of 7.23% centred at 477 nm, which was much higher than the EQE of a PVK device (4.95%). Our results demonstrate that modulating the energy level and charge injection of the HTL in the device is a promising method for obtaining efficient blue PeLEDs.