Improved stability and efficiency of inverted triple-cation mixed-halide perovskite solar cells with CsI-modified NiOx hole transporting layer.

Addressing the critical challenge of mitigating defect generation and enhancing the extended durability of perovskite solar cells (PeSCs) requires effective passivation materials. In our study, we investigated the impact of varying concentrations of cesium iodide (CsI), an alkali halide, on the interface layer among the hole transporting layer (HTL) and the perovskite film in a triple-cation lead hybrid halide Cs0.15FA0.81MA0.04Pb(I2.86Br0.14)3 perovskite layer. Our findings revealed that the introduction of CsI into the NiOx HTL led to improved crystallinity and a reduction in defects within the perovskite film. Consequently, the photovoltaic performance of the CsI-modified PeSC exhibited a notable enhancement. Specifically, the photoelectric conversion efficiency (PCE) increased from 18.7 % in the original PeSC, which lacked CsI modification, to 20.5 %. Moreover, this improvement in PCE was accompanied by excellent stability, with the CsI-modified PeSC retaining 80 % of its opening PCE even afterward 144 h of testing.

Methylammonium halide salt interfacial modification of perovskite quantum dots/triple-cation perovskites enable efficient solar cells.

Perovskite solar cells (PeSCs) have been introduced as a new photovoltaic device due to their excellent power conversion efficiency (PCE) and low cost. However, due to the limitations of the perovskite film itself, the existence of defects was inevitable, which seriously affects the number and mobility of carriers in perovskite solar cells, thus restricting PeSCs improved efficiency and stability. Interface passivation to improve the stability of perovskite solar cells is an important and effective strategy. Here, we use methylammonium halide salts (MAX, X = Cl, Br, I) to effectively passivate defects at or near the interface of perovskite quantum dots (PeQDs)/triple-cation perovskite films. The MAI passivation layer increased the open circuit voltage of PeQDs/triple-cation PeSC by 63 mV up to 1.04 V, with a high short-circuit current density of 24.6 mA cm-2 and a PCE of 20.4%, which demonstrated a significant suppression of interfacial recombination.

Two-Dimensional (PEA)2PbBr4 Perovskites Sensors for Highly Sensitive Ethanol Vapor Detection.

Two-dimensional (2D) perovskite have been widely researched for solar cells, light-emitting diodes, photodetectors because of their excellent environmental stability and optoelectronic properties in comparison to three-dimensional (3D) perovskite. In this study, we demonstrate the high response of 2D-(PEA)2PbBr4 perovskite of the horizontal vapor sensor was outstandingly more superior than 3D-MAPbBr3 perovskite. 2D transverse perovskite layer have the large surface-to-volume ratio and reactive surface, with the charge transfer mechanism, which was suitable for vapor sensing and trapping. Thus, 2D perovskite vapor sensors demonstrate the champion current response ratio R of 107.32 under the ethanol vapors, which was much faster than 3D perovskite (R = 2.92).

Efficient Perovskite Solar Cells via Phenethylamine Iodide Cation-Modified Hole Transport Layer/Perovskite Interface.

Perovskite solar cells (PeSCs) were fabricated by using Cs x FA1-x PbI3-x Cl x as the photoactive layer, and the effects of different proportions of cesium chloride (CsCl)/formamidinium iodide on perovskites were investigated. Cesium (Cs) can stabilize the α phase of the perovskite, while chlorine (Cl) can increase the size and crystallinity of perovskite crystals and reduce non-radiative cladding, thereby improving the performance of the overall device. The maximum power conversion efficiency (PCE) measured for Cs0.2FA0.8PbI2.8Cl0.2-based PeSCs was 18.9%. To further improve the photovoltaic characteristics of PeSCs, Cs0.2FA0.8PbI2.8Cl0.2-based PeSCs were introduced into different concentrations of phenethylammonium iodide (PEAI) to modify the interface between the NiO x hole transport layer (HTL) and the perovskite photoactive layer, which can simultaneously promote excellent crystallinity of the perovskite layer and passivated interfacial defects, reducing recombination near the perovskite/HTL interface in PeSCs, thereby increasing the efficiency of the device. Compared with the control Cs0.2FA0.8PbI2.8Cl0.2-based PeSC, the PCE of PeSC with the PEAI (10 mg/mL)-modified NiO x /perovskite interface increased significantly from 18.9 to 20.2%.

Wide-Angle Mini-Light-Emitting Diodes without Optical Lens for an Ultrathin Flexible Light Source.

This report outlines a proposed method of packaging wide-angle (WA) mini-light-emitting diode (mini-LED) devices without optical lenses to create a highly efficient, ultrathin, flexible planar backlight for portable quantum dot light-emitting diode (QLED) displays. Since the luminous intensity curve for mini-LEDs generally recommends a beam angle of 120°, numerous LEDs are necessary to achieve a uniform surface light source for a QLED backlight. The light-guide layer and diffusion layer were packaged together on a chip surface to create WA mini-LEDs with a viewing angle of 180°. These chips were then combined with a quantum dot (QD) film and an optical film to create a high-efficiency, ultrathin, flexible planar light source with excellent color purity that can be used as a QLED display backlight. A 6 in (14.4 cm) light source was used as an experimental sample. When 1.44 W was supplied to the sample, the 3200-piece WA mini-LED with a flexible planar QLED display had a beam angle of 180° on the luminous intensity curve, a planar backlight thickness of 0.98 mm, a luminance of 10,322 nits, and a luminance uniformity of 92%.

Enhancement of the light extraction characteristics and wide-angle emissive behavior of deep-ultraviolet flip-chip light-emitting diodes by using optimized optical films.

We propose the use of optical films to enhance the light extraction efficiency (LEE) and wide-angle emission of traditional packaged deep-ultraviolet light-emitting diodes (DUV-LEDs). Total internal reflection occurs easily in DUV-LEDs because they contain sapphire, which has a high refractive index. DUV-LEDs also contain an aluminum nitride (AlN) ceramic substrate, which has high light absorption in the ultraviolet band. Photons are absorbed by the sapphire and AlN ceramic substrate, which reduces the LEE of DUV-LEDs. By adding a brightness enhancement film (BEF) on the sapphire surface and a high-reflection film (HRF) on the surface of the AlN ceramic substrate, the LEE of DUV-LEDs can be increased. Moreover, we designed a single-layer metal reflective film (SMRF) on the upper surface of the quartz glass in order to achieve wide-angle emission. Experimental results indicated that compared with traditional packaged DUV-LEDs, the light output power and external quantum efficiency of DUV-LEDs with a plated BEF, HRF, and SMRF increased by 18.3% and 18.2%, respectively. Moreover, an emission angle of 160° was achieved. In a reliability test, DUV-LEDs maintained more than 95% of the initial forward voltage and light output power after 1000 h of operation at 25°C, which indicated that the addition of an optical film can improve the light efficiency and long-term reliability of DUV-LEDs.

The Effects of Temperature on the Growth of a Lead-Free Perovskite-Like (CH3NH3)3Sb2Br9 Single Crystal for An MSM Photodetector Application.

We have fabricated a photodetector based on (CH3NH3)3Sb2Br9 (MA3Sb2Br9) lead-free perovskite-like single crystal, which plays an important role in the optoelectronic characteristics of the photodetector as a perovskite-like photosensitive layer. Here, MA3Sb2Br9 single crystals were synthesized by an inverse temperature crystallization process with a precursor solution at three different growth temperatures, 60 °C, 80 °C, and 100 °C. As a result, a MA3Sb2Br9 single crystal with an optimum growth temperature of 60 °C presented a low trap density of 2.63 × 1011 cm-3, a high charge carrier mobility of 0.75 cm2 V-1 s-1, and excellent crystal structure and optical absorption properties. This MA3Sb2Br9 perovskite-like photodetector displayed a low dark current of 8.09 × 10-9 A, high responsivity of 0.113 A W-1, and high detectivity of 4.32 × 1011 Jones.

Red Light-Emitting Diodes with All-Inorganic CsPbI3/TOPO Composite Nanowires Color Conversion Films.

This work presents a method for obtaining a color-converted red light source through a combination of a blue GaN light-emitting diode and a red fluorescent color conversion film of a perovskite CsPbI3/TOPO composite. High-quality CsPbI3 quantum dots (QDs) were prepared using the hot-injection method. The colloidal QD solutions were mixed with different ratios of trioctylphosphine oxide (TOPO) to form nanowires. The color conversion films prepared by the mixed ultraviolet resin and colloidal solutions were coated on blue LEDs. The optical and electrical properties of the devices were measured and analyzed at an injection current of 50 mA; it was observed that the strongest red light intensity was 93.1 cd/m2 and the external quantum efficiency was 5.7% at a wavelength of approximately 708 nm when CsPbI3/TOPO was 1:0.35.

Using Thermally Crosslinkable Hole Transporting Layer to Improve Interface Characteristics for Perovskite CsPbBr3 Quantum-Dot Light-Emitting Diodes.

In this paper, a thermally crosslinkable 9,9-Bis[4-[(4-ethenylphenyl)methoxy]phenyl]-N2,N7-di-1-naphthalenyl-N2,N7-diphenyl-9H-fluorene-2,7-diamine (VB-FNPD) film served as the hole transporting layer (HTL) of perovskite CsPbBr3 quantum-dot light-emitting diodes (QD-LEDs) was investigated and reported. The VB-FNPD film crosslinked at various temperatures in the range of 100~230 °C followed by a spin-coating process to improve their chemical bonds in an attempt to resist the erosion from the organic solvent in the remaining fabrication process. It is shown that the device with VB-FNPD HTL crosslinking at 170 °C has the highest luminance of 7702 cd/m2, the maximum current density (J) of 41.98 mA/cm2, the maximum current efficiency (CE) of 5.45 Cd/A, and the maximum external quantum efficiency (EQE) of 1.64%. Our results confirm that the proposed thermally crosslinkable VB-FNPD is a candidate for the HTL of QD-LEDs.

High-Uniformity Planar Mini-Chip-Scale Packaged LEDs with Quantum Dot Converter for White Light Source.

This study proposes a novel direct-lit mini-chip-scale packaged light-emitting diode (mini-CSPLED) backlight unit (BLU) that used quantum dot (QD) film, diffusion plate, and two prism films to improve brightness uniformity. Three different luminous intensity units, 120° mini-CSPLED, 150° mini-CSPLED, and 180° mini-CSPLED with different emission angle structures were fabricated using a CSP process. In terms of component characteristics, although the 180° mini-CSPLED light output power is about loss 4% (at 10 mA) compared with 150° mini-CSPLED, it has a large emission angle that forms a planar light source that contributes to improving the BLU brightness uniformity and reduced quantity of LEDs at the same area. In terms of BLU analysis, the blue mini-CSPLEDs with different emission angles excite the different QD film thicknesses; the chromaticity coordinates conversion to the white light region. The BLU brightness increases as the QD film thickness increases from 60, 90, and 150 µm. This result can achieve a brightness uniformity of 86% in a 180° mini-CSPLED BLU + 150-µm-thick QD films as compared to the 120° mini-CSPLED BLU and 150° mini-CSPLED BLU.

Influence of PMMA on All-Inorganic Halide Perovskite CsPbBr3 Quantum Dots Combined with Polymer Matrix.

The poor stability of CsPbX3 quantum dots (QDs-CsPbX3) under wet conditions is still considered to be a key issue. In order to overcome this problem, this study presents a high molecular weight polymer matrix (polymethylmethacrylate, PMMA) incorporated into the QDs-CsPbBr3 to improve its stability and maintain its excellent optical properties. In this study, the Cs2CO3, PbO, Tetrabutylammonium Bromide (TOAB) powder, oleic acid, and toluene solvent were uniformly mixed and purified to prepare high-quality QDs powders. Then, hexane was used as a dispersing agent for the QD powder to complete the perovskite QDs-CsPbBr3 solution. Finally, a solution with different proportions of quantum dots CsPbBr3 and PMMA was prepared and discussed. In the preparation of thin films, firstly, a thin film with the structure of glass/QD-CsPbBr3/PMMA was fabricated in a glove box using a well-developed QDs-CsPbBr3 solution by changing the ratio of CsPbBr3:PMMA. The material analysis of QDs-CsPbBr3 thin films was performed with photoluminescence (PL), transmittance, absorbance, and transmission electron microscopy (TEM). The structures and morphologies were further examined to study the effect of doped PMMA on perovskite QDs-CsPbBr3.

Enhanced Efficiency of MAPbI3 Perovskite Solar Cells with FAPbX3 Perovskite Quantum Dots.

We describe a method to enhance power conversion efficiency (PCE) of MAPbI3 perovskite solar cell by inserting a FAPbX3 perovskite quantum dots (QD-FAPbX3) layer. The MAPbI3 and QD-FAPbX3 layers were prepared using a simple, rapid spin-coating method in a nitrogen-filled glove box. The solar cell structure consists of ITO/PEDOT:PSS/MAPbI3/QD-FAPbX3/C60/Ag, where PEDOT:PSS, MAPbI3, QD-FAPbX3, and C60 were used as the hole transport layer, light-absorbing layer, absorption enhance layer, and electron transport layer, respectively. The MAPbI3/QD-FAPbX3 solar cells exhibit a PCE of 7.59%, an open circuit voltage (Voc) of 0.9 V, a short-circuit current density (Jsc) of 17.4 mA/cm², and a fill factor (FF) of 48.6%, respectively.

Slow Electron Making More Efficient Radiation Emission.

In conventional emitting devices, the mobility of electron is much higher than that of hole, which increases the non-recombination rate. To generate slow electrons, we demonstrate an electron retarding n-electrode (ERN) on the n-GaN layer of InGaN blue light emitting diode (LED), making more efficient radiation emission. Transparent conductive oxides are estimated to be more suitable for ERN materials. However, for ERN materials used in InGaN LEDs, three requirements should be satisfied, i.e., Ohmic contact to n-GaN, dilute magnetic doping, and good electrical conductivity. The pulsed-laser deposited cobalt-doped ZnO film prepared at 400 °C was chosen as the ERN. The electron retarding of 120-nm-thick ERN/n-GaN reached 19.9% compared to the n-GaN. The output powers (@350 mA) of LEDs with and without the ERN were 246.7 and 212.9 mW, while their wall-plug efficiencies were 18.2% and 15.1%, respectively. Moreover, owing to the efficient filling of electrons in the quantum wells by inserting the ERN, the bandgap of quantum wells was enlarged, inducing the blue-shift in the emission wavelength of LED. The slow electron generated from the ERN technique paves the way to solve the problem of large difference between electron and hole velocities and improve the optoelectronic performance of emitting devices.

Recording Characteristics, Microstructure, and Crystallization Kinetics of Ge/GeCu Recording Film Used for Write-Once Blu-Ray Disc.

A Ge67Cu33 (16 nm) layer and a Ge (3 nm)/Ge67Cu33 (16 nm) bilayer were grown by sputtering at room temperature and used as the recording films for write-once blue laser media. In comparison to the crystallization temperature of Ge in a GeCu film (380.7 °C-405.1 °C), the crystallization temperature of Ge in a Ge/GeCu bilayer could be further decreased to 333.7 °C-382.8 °C. The activation energies of Ge crystallization were 3.51 eV ± 0.05 eV and 1.50 eV ± 0.04 eV for the GeCu and the Ge/GeCu films, respectively, indicating that the Ge/GeCu bilayer possesses a higher feasibility in high-speed optical recording applications. Moreover, the lower activation energy would lead to a larger grain size of Ge crystallization in the Ge/GeCu bilayer after the annealing process. Between the as-deposited and the annealed states, the optical contrasts (@ 405 nm) of the GeCu and the Ge/GeCu films were 26.0% and 47.5%, respectively. This reveals that the Ge/GeCu bilayer is more suitable for the recording film of a write-once blu-ray disc (BD-R) in comparison with the GeCu film. Based on the dynamic tests performed for 2× and 4× recording speeds, the optimum jitter values of the BD-R with the Ge/GeCu recording film were 7.4% at 6.3 mW and 7.6% at 8.6 mW, respectively.

External stress effects on the optical and electrical properties of flexible InGaN-based green light-emitting diodes.

Flexible InGaN-based green light emitting diodes (LEDs) were fabricated by transferring epilayer to a flexible polyimide substrate with laser lift-off (LLO) and double-transfer technologies. We present a method of increasing light output power in flexible LEDs without modifying their epitaxial layers. These improvements are achieved by reducing the quantum-confined Stark effect by reducing piezoelectric polarization that results from compressive stress in the GaN epilayer. The compressive stress is relaxed due to the external stress induced by increasing bending displacement of flexible substrate. The light output power of the flexible LED at an injection current of 150 mA is increased by approximately 42.2%, as the external bending went to the case of effective length of 15 mm. The experimental results demonstrated that applying external tensile stress effectively compensates for the compressive strain and changes the piezoelectric field in the InGaN/GaN MQWs region, thereby increases the probability of radiative recombination.

Performance of GaN-based light-emitting diodes fabricated using GaN epilayers grown on silicon substrates.

Light extraction of GaN-based light-emitting diodes grown on Si(111) substrate (GaN-on-Si based LEDs) is presented in this study. Three different designs of GaN-on-Si based LEDs with the lateral structure, lateral structure on mirror/Si(100) substrate, and vertical structure on mirror/Si(100) substrate were epitaxially grown by metalorganic chemical vapor deposition and fabricated using chemical lift-off and double-transfer techniques. Current-voltage, light output power, far-field radiation patterns, and electroluminescence characteristics of these three LEDs were discussed. At an injection current of 700 mA, the output powers of LEDs with the lateral structure on mirror/Si(100) substrate and vertical structure on mirror/Si(100) substrate were measured to be 155.07 and 261.07 mW, respectively. The output powers of these two LEDs had 70.63% and 187.26% enhancement compared to that of LED with the lateral structure, respectively. The result indicated this vertical structure LED was useful in improving the light extraction due to an enhancement in light scattering efficiency while the high-reflection mirror and diffuse surfaces were employed.

High performance GaN-based flip-chip LEDs with different electrode patterns.

A high-performance flip-chip light-emitting diode (FCLED) with a Ni/Ag metallic film as high reflectivity mirror (92.67%) of p-type electrode was successfully fabricated. The effect of geometric electrode patterns on the blue InGaN/GaN LEDs was investigated and analyzed qualitatively its current spreading in the active region. With different electrode patterns, these devices were experimented and simulated by simple electrical circuits in order to confirm its current-voltage characteristics and light emission pattern. It was found that the forward voltages of these FCLEDs were about 3.6 V (@350 mA). The light output power of FCLEDs with circle-round type electrode was 368 mW at an injection current of 700 mA. From these optoelectronic measurement and thermal infrared images, we proposed some design methodologies for improved current spreading, light output power, droop efficiency and thermal performance.

White thin-film flip-chip LEDs with uniform color temperature using laser lift-off and conformal phosphor coating technologies.

We fabricated a phosphor-conversion white light emitting diode (PC-WLED) using a thin-film flip-chip GaN LED with a roughened u-GaN surface (TFFC-SR-LED) that emits blue light at 450 nm wavelength with a conformal phosphor coating that converts the blue light into yellow light. It was found that the TFFC-SR-LED with the thin-film substrate removal process and surface roughening exhibits a power enhancement of 16.1% when compared with the TFFC-LED without a sapphire substrate. When a TFFC-SR-LED with phosphors on a Cu-metal packaging-base (TFFC-SR-Cu-WLED) was operated at a forward-bias current of 350 mA, luminous flux and luminous efficacy were increased by 17.8 and 11.9%, compared to a TFFC-SR-LED on a Cup-shaped packaging-base (TFFC-SR-Cup-WLED). The angular correlated color temperature (CCT) deviation of a TFFC-SR-Cu-WLED reaches 77 K in the range of -70° to + 70° when the average CCT of white LEDs is around 4300 K. Consequently, the TFFC-SR-LED in a conformal coating phosphor structure on a Cu packaging-base could not only increase the luminous flux output, but also improve the angular-dependent CCT uniformity, thereby reducing the yellow ring effect.

Enhanced light output power of thin film GaN-based high voltage light-emitting diodes.

The characteristics of high-voltage light-emitting diodes (HVLEDs) consisting of a 64-cell LED array were investigated by employing various LED structures. Two types of HVLED were examined: a standard HVLED with a single roughened indium tin oxide (ITO) surface grown on a sapphire substrate and a thin-film HVLED (TF-HVLED) with a roughened n-GaN and ITO double side transferred to a mirror/silicon substrate. At an injection current of 24 mA, the output powers of the HVLEDs fabricated using a sapphire substrate and those fabricated using a mirror/silicon substrate were 170 and 216 mW, respectively. Because the TF-HVLED exhibited improved thermal dissipation and light extraction, it produced a greater output power than the HVLED fabricated using the sapphire substrate did.

Effects of spin-polarized injection and photo-ionization of MnZnO film on GaN-based light-emitting diodes.

This study discusses the effect of spin-polarized injection and photo-ionization on MnZnO films formed on the surface of GaN-based light-emitting diodes (LEDs). In a magnetic field, the optical output power of GaN-based LEDs increased by about 60% and 50% at injection currents of 20 and 100 mA, respectively. Spin-polarized injection from a MnZnO film and photo-ionization in GaN-based LED can efficiently improve the optical output power of a GaN-based LED. At forward bias of 3.4 V, the forward current of GaN-based LED with MnZnO film in a magnetic field of 0.5 T includes an injection current of 33.71 mA, spin-polarized current of 0.97 mA, and photo-ionized current of 0.4 mA.