School of Energy and Chemical Engineering (Energy Engineering)

Line-cut profiles for GIWAXS patterns of 2D perovskite films deposited on PEDOT:PSS and 36ClCzEPA SAM HIL. XPS spectra corresponding to (a) Pb 4f, (b) Br 3d, and (c) Cl 2p, and (d) measured halide ratio of perovskite films deposited on PEDOT:PSS with different additives, L-phenylalanine, L-tyrosine and L-dopa.

Introduction

Structure and Properties of Metal Halide Perovskite

Structure of Metal Halide Perovskite
Properties of Metal Halide Perovskite

The acceptable range of tolerance factor is 0.78 < t < 1.05 for the formation of the stable perovskite structure (Figure 1.1b). Due to this electronic structure, MHP shows a strong tolerance to crystal defects compared to other typical semiconductors (GaAs, CdTe) (Figure 1.4a).

Metal Halide Perovskite Light-Emitting Diodes

Operating Principles of Metal Halide Perovskite Light-Emitting Diodes
Characteristics of Metal Halide Perovskite Light-Emitting Diodes

The photon generation efficiency is known as the internal quantum efficiency (IQE), which is the ratio of the number of photons generated in the perovskite emitting layer per unit time to the number of electrons injected into the device per unit time. Furthermore, in the case of PeLEDs, the color of the perovskite emitting layer, which is determined by its bandgap, even affects the turn-on voltage.

Blue Emissive Metal Halide Perovskite Light-Emitting Diodes

Limitations of Blue Emissive Metal Halide Perovskite Materials
Structure and Properties of Quasi-Two-Dimensional Perovskite Materials

The chlorine-incorporated perovskite materials have a wide band gap, representing a deep HOMO energy level (> 6.2 eV) (Figure 1.10a). As shown in Figure 1.10b, due to the large potential barrier from HTL to the blue emitting perovskite layer, the injected holes can be accumulated without flowing into the perovskite emitting layer.

Manipulated Interface for Enhanced Energy Cascade in Quasi-2D Blue Perovskite

Research Background
Experimental Details
Results and Discussion
Conclusion

Figures 2.7a, b show the TA spectra of p- and m-PEDOT:PSS perovskite films at variable delay times after photoexcitation at 375 nm. TA spectra of quasi-2D perovskite films deposited on (a) p- and (b) m-PEDOT:PSS at variable time delays as indicated in the panels.

A Multifunctional Self-Assembled Monolayer for Highly Luminescent Pure-Blue

Conclusion

XPS spectra of the 36ClCzEPA SAM on the ITO surface were performed to investigate the presence of the SAM and its binding affinity. Surprisingly, a hypsochromic shift and the absence of the n = 1 2D phase at 389 nm were observed for the 2D perovskite film on 36ClCzEPA SAM (Figure 3.4b). In addition, GIWAXS measurements were performed to gain further insight into the preferred orientation of perovskite films deposited on PEDOT:PSS and 36ClCzEPA SAMs.

Triexponential fitting parameters for PL lifetimes of perovskite films deposited on PEDOT:PSS and 36ClCzEPA SAM on ITO substrates. The 2D perovskite film on 36ClCzEPA SAM showed no indium signals, whereas the perovskite film on PEDOT:PSS clearly exhibited the appearance of indium species. Schematic illustrations of the hole injection process in PeLEDs using the PEDOT:PSS and 36ClCzEPA SAM HILs.

Pure-Blue Electroluminescence of Quasi-2D Perovskites with Modulated Phase

Research Background

Pure blue electroluminescence of quasi-2D perovskites with modulated phase distribution via surface polarity of PEDOT:PSS. The population and distribution of 2D phases are crucial in determining the luminescent properties of quasi-2D perovskite films. For example, small perovskites are typically formed on a substrate, which represents a high wettability for a polar solvent.113 They then eventually grow into phases with a lower n2D value, causing the light-emitting phase to have a lower n value, resulting in a hypsochromic shift of the luminescent spectra Therefore, the luminescent properties of the deposited quasi-2D perovskite films are susceptible to substrates with different surface polarity.

Herein, we investigate the influence of the surface polarity of PEDOT:PSS on the population of 2D phases and the luminescence properties of resulting quasi-2D perovskite films by incorporating surface modifiers, L-phenylalanine, L-tyrosine and L-dopa, into PEDOT:PSS. The introduction of the L-dopa additive with electron-donating hydroxyl groups allowed the coordination bond with the sulfonate group of PSS moieties, resulting in a higher surface polarity for the PEDOT:PSS substrate. As a result, the possible formation of quasi-2D perovskite films using L-dopa and with a lower-n-dominated phase distribution represented a hypsochromic shift of the luminescence spectrum.

Experimental Details

DFT calculations were performed using the Vienna ab initio simulation package (VASP).80,116 The electron-ion interaction was described by the projector-augmented-wave (PAW) method.117 The generalized gradient approximation (GGA) Perdew-Burke- Ernzerhof functional (PBE ) exchange correlation functional81 was used with a plane wave base cutoff energy of 450 eV. The Brillouin zone was sampled by a set of 2 x 2 x 1 k-points with the Monkhorst-Pack scheme.118 The self-consistent field calculation was performed with the convergence criterion of 1.0 x 10–5eV. To model the quasi-2D perovskite surface, we obtained the (PEA)2PbBr4 bulk structure from the work of Kishimoto et al.119 To elucidate the low-n2D phase and the high-n2D phase, we constructed surface models constructed including each two- and four-layer PbBr6 octahedrons from the bulk structure and optimized the surface model.

Then, Cl atom doping was performed in the structure to make Br and Cl in the ratio 1:1. In the n= 4 surface model, the two middle layers were fixed to consider the effect of film area during the optimization process. To mimic the hydroxy group on the benzene ring of the additives, which forms a coordination bond with the PEDOT:PSS substrate, the hydroxy group on the benzene ring in L-dopa is located in the opposite direction to the quasi-2D surface of the perovskite.

Results and Discussion

Surprisingly, as the surface polarity of the PEDOT:PSS substrate increased (from L-phenylalanine to L-dopa), the gradual increase in the relative absorption intensity of the n=3 phase and the decrease in the shoulder at ca. 462 nm (n≥ 4.5 phases) can be observed (Figure 4.3b). FWHM of the lower n-phase peak for perovskite films deposited on PEDOT:PSS with different additives, (a) L-phenylalanine, (b) L-tyrosine, and (c) L-dopa. Interestingly, up to 80% of L-phenylalanine follows the properties of PEDOT:PSS with pure L-dopa.

UPS spectra of PEDOT:PSS with different additives, L-phenylalanine, L-dopa and the mixed state (L-phenylalanine:L-dopa = 80:20 v/v%): (a) Secondary electronic edge and (b) valence edge band drawn relative to the Au reference. CIE coordinate of PeLED using PEDOT:PSS with different additives, L-phenylalanine, L-tyrosine, L-dopa and mixed state (L-phenylalanine:L-dopa = 80:20 v/v%). Summary of CIE coordinates of PeLEDs using PEDOT:PSS with different additives, L-phenylalanine, L-tyrosine, L-dopa and mixed state (L-phenylalanine:L-dopa = 80:20 v/v%).

Conclusion

Phase Rearrangement for Minimal Exciton Loss in Quasi-2D Perovskite toward

Research Background

Phase Rearrangement for Minimal Exciton Loss in Quasi-2D Perovskites Towards Efficient Deep Blue LEDs via Halide Post-Treatment. The quantum confinement effect has been considered a strategy to widen the optical bandgap of luminescent materials in the field of perovskite quantum dots.146 This feature enables continuous size-dependent bandgap control, which is useful for the design of perovskite emitters. deep blue in color. However, in the case of quasi-2D perovskites, the non-monotonic variation in the optical bandgap of each 2D phase with different n prevents precise modulation of their optical properties for desired colors.147 Chlorine incorporation is an alternative approach for tuning deep blue color. with quasi-2D perovskites.

Here, we propose a simple and versatile post-processing strategy to realize efficient dark blue quasi-2D PeLEDs based on the halide exchange process without destroying the perovskite lattice. During this process, in a time span of a few seconds, the supplied chlorine content controls the color of the perovskite films towards the desired dark blue emission, leading to efficient PL by thorough passivation of chlorine vacancies. The aforementioned synergistic post-processing effects result in highly efficient dark blue PeLEDs with a maximum EQE of 4.97%.

Experimental Details

The pump beam flux was attenuated with neutral density filters to 5 μJ/cm2 to limit multi-excitonic effects. The time delay of the probe pulse relative to the pump pulse was adjusted by a computer-controlled optical delay stage. To avoid anisotropic effects, the polarization of the pump beam was set to 54.7° (magic angle) with respect to the polarization of the probe beam.

PL spectra were measured using a fluorometer with a xenon lamp as the excitation source (nF900, Edinburgh Instruments). UPS spectra were measured using a spectrometer (ESCALAB 250XI, Thermo Fisher Scientific) under the same conditions. The angle of incidence (0.20°) of the X-ray beam was chosen to allow complete penetration into the film.

Results and Discussion

In addition, the PL stability of the HPR-treated perovskite film is also improved after continuous thermal annealing at 120 for 20 min. AFM image of the as-prepared sky-blue quasi-2D perovskite film. a) Optical bands and (b, c) UPS spectra of as-deposited control and HPR-treated perovskite films. The appearance of a diffraction peak for the n = 3 phase instead of the peak for the n = 2 phase for the HPR-processed perovskite film indicates that it is dominated by higher n-phases.

This may be due to a slight increase in the chlorine content of the HPR-treated perovskite film; The confinement of the n= 2 phase in the HPR-treated perovskite film is amply reflected in the corresponding increase in the PIB band intensity of the n= 3 (Figure 5.8b). The relative amplitudes of the PIB for the n = 2 and 3 phases indicate that the n = 3 phase is preferentially populated in the HPR-treated perovskite film.

Conclusion

Highly Stable Bulk Perovskite for Blue LEDs with Anion-exchange Method

Conclusion

UV–vis absorption and PL reference spectra (Ref. 520) and anion-exchanged bulk perovskite films (A.E. 470 and A.E. 490 conditions). Summary biexponential fitting parameters for TRPL lifetimes of reference (Ref. 520) and anion-exchanged bulk perovskite films, AE Negative ion TOF-SIMS spectra and depth profiles of (a) reference (Ref. 520) and anion-exchanged bulk perovskite films, (b) AE

Reference surface images (Figure 6.12a) and bulk anion-exchanged perovskite films (Figures 6.12b,c) were obtained from SEM measurements. UPS spectra (left: secondary electron cutoff region and right: onset region) of reference (Ref. 520) and multiple anion-exchanged perovskite films, A.E. spectra. EL operation under different applied voltages of PeLEDs optimized with polycrystalline anion-exchanged perovskite films ( a) A.E.

Summary

Rearrangement of Low-Dimensional Phase Distribution of Quasi-2D Perovskites for Efficient Sky-Blue Perovskite Light-Emitting Diodes. Vivid and fully saturated blue light-emitting diodes based on ligand-modified halide perovskite nanocrystals. Conjugated polyelectrolytes as multifunctional passivating and hole-transporting layers for efficient perovskite light-emitting diodes.

High-performance blue perovskite light-emitting diodes enabled by efficient energy transfer between coupled quasi-2D perovskite layers. Modulation of recombination zone position for quasi-two-dimensional blue perovskite light-emitting diodes with efficiencies above 5%. Engineering Annealing and Surface Passivation Towards Efficient and Stable Quasi-2d Perovskite Light Emitting Diodes.