Open Access Issue
980 nm Near-Infrared Light-Emitting Diode Using All-Inorganic Perovskite Nanocrystals Doped with Ytterbium Ions
Tsinghua Science and Technology 2024, 29 (1): 207-215
Published: 21 August 2023

All-inorganic perovskite (CsPbX 3) nanocrystals (NCs) have recently been widely investigated as versatile solution-processable light-emitting materials. Due to its wide-bandgap nature, the all-inorganic perovskite NC Light-Emitting Diode (LED) is limited to the visible region (400–700 nm). A particularly difficult challenge lies in the practical application of perovskite NCs in the infrared-spectrum region. In this work, a 980 nm NIR all-inorganic perovskite NC LED is demonstrated, which is based on an efficient energy transfer from wide-bandgap materials (CsPbCl 3 NCs) to ytterbium ions (Yb 3+) as an NIR emitter doped in perovskite NCs. The optimized CsPbCl 3 NC with 15 mol%Yb 3+ doping concentration has the strongest 980 nm photoluminescence (PL) peak, with a PL quantum yield of 63%. An inverted perovskite NC LED is fabricated with the structure of ITO/PEDOT: PSS/poly-TPD/CsPbCl 3:15 mol%Yb 3+ NCs/TPBi/LiF/Al. The LED has an External Quantum Efficiency (EQE) of 0.2%, a Full Width at Half Maximum (FWHM) of 47 nm, and a maximum luminescence of 182 cd/m 2. The introduction of Yb 3+ doping in perovskite NCs makes it possible to expand its working wavelength to near-infrared band for next-generation light sources and shows potential applications for optoelectronic integration.

Open Access Issue
Brightness and Lifetime Improved Light-Emitting Diodes from Sr-Doped Quasi-Two-Dimensional Perovskite Layers
Tsinghua Science and Technology 2023, 28 (1): 131-140
Published: 21 July 2022

Green Perovskite Light-Emitting Diodes (PeLEDs) have attracted wide attention for full spectrum displays. However, the inferior film morphology and luminescence property of quasi-two-dimensional (quasi-2D) perovskite layers limit the photoelectric property of the PeLEDs. In this paper, the effect of strontium (Sr) doped in quasi-2D perovskite layers is investigated to obtain a high-quality active layer. The morphologies and optical properties of Sr-doped quasi-2D perovskite films with different concentrations are studied. With the addition of strontium, more low-dimensional-layer perovskite phases ( n=2 and n=3) appear in quasi-2D perovskite films, providing efficient intraband carrier funneling pathway and facilitating radiative recombination. The photoluminescence (PL) peak intensity of optimized Sr-doped quasi-2D perovskite layers increases 50% compared with the non-strontium counterpart. Moreover, green PeLEDs based on a Sr-doped quasi-2D perovskite layer reach a maximum luminance ( Lmax) of 2943.77 cd/m 2, which is three times of the control device. The electroluminescence (EL) peaks of Maximum External Quantum Efficiency (MEQE) and Lmax of Sr-doped PeLEDs exhibite a slight shift, indicating the excellent stability and performance of Sr-doped devices. The optimized device can continuously operate for 360 s at MEQE driving voltage, resulting in a half-lifetime of 60 s, which is 3-fold greater than that of the control PeLEDs.

Open Access Issue
Investigation on n-Type (–201) β-Ga2O3 Ohmic Contact via Si Ion Implantation
Tsinghua Science and Technology 2023, 28 (1): 150-154
Published: 21 July 2022

Heavy doped n-type β-Ga 2O 3 (HD-Ga 2O 3) was obtained by employing Si ion implantation technology on unintentionally doped β-Ga 2O 3 single crystal substrates. To repair the Ga 2O 3 lattice damage and activate the Si after implantation, the implanted substrates were annealed at 950℃, 1000℃, and 1100℃, respectively. High-resolution X-ray diffraction and high-resolution transmission electron microscopy show that the ion-implanted layer has high lattice quality after high-temperature annealing at 1000℃. The minimum specific contact resistance is 9.2×10–5Ω·cm2, which is attributed to the titanium oxide that is formed at the Ti/Ga 2O 3 interface via rapid thermal annealing at 480℃. Based on these results, the lateral β-Ga 2O 3 diodes were prepared, and the diodes exhibit high forward current density and low specific on-resistance.

Open Access Issue
Interface Modification of TiO 𝟐 Electron Transport Layer with PbCl 𝟐 for Perovskiote Solar Cells with Carbon Electrode
Tsinghua Science and Technology 2022, 27 (4): 741-750
Published: 09 December 2021

Perovskite Solar Cells (PSCs) have attracted considerable attention because of their unique features and high efficiency. However, the stability of perovskite solar cells remains to be improved. In this study, we modified the TiO 2 Electron Transport Layer (ETL) interface with PbCl 2. The efficiency of the perovskite solar cells with carbon electrodes increased from 11.28% to 13.34%, and their stability obviously improved. The addition of PbCl 2 had no effect on the morphology, crystal structure, and absorption property of the perovskite absorber layer. However, it affected the band energy level alignment of the solar cells and accelerated the electron extraction and transfer at the interface between the perovskite layer and the ETL, thus enhancing the overall photovoltaic performance. The interfacial modification of ETL with PbCl 2 is a promising way for the potential commercialization of low-cost carbon electrode-based perovskite solar cells.

Open Access Issue
Effect of Chloride Ion Concentrations on Luminescence Peak Blue Shift of Light-Emitting Diode Using Anti-Solvent Extraction of Quasi-Two-Dimensional Perovskite
Tsinghua Science and Technology 2021, 26 (4): 496-504
Published: 04 January 2021

In recent years, Perovskite Light-Emitting Diodes (PeLEDs) have received considerable attention in academia. However, with the development of PeLEDs, commercial applications of full-color PeLED technology are largely limited by the progress of blue-emitting devices, due to the uncontrollably accurate composition, unstable properties, and low luminance. In this article, we add Cesium chloride (CsCl) to the quasi-two-dimensional (quasi-2D) perovskite precursor solution and achieve the relatively blue shifts of PeLED emission peak by introducing chloride ions for photoluminescence (PL) and electroluminescence (EL). We also found that the introduction of chlorine ions can make quasi-2D perovskite films thinner with smoother surface of 0.408 nm. It is interesting that the EL peaks and intensities of PeLED are adjustable under different driving voltages in high concentration chlorine-added perovskite devices, and different processes of photo-excited, photo-quenched, and photo-excited occur sequentially with the increasing driving voltage. Our work provides a path for demonstrating full-color screens in the future.

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