Charge Generation Layer Research Articles

Charge Generation and Enhancement of Key Components of Triboelectric Nanogenerators: A Review.

The past decade has witnessed remarkable progress in high-performance Triboelectric nanogenerators (TENG) with the design and synthesis of functional dielectric materials, the exploration of novel dynamic charge transport mechanisms, and the innovative design of architecture, making it one of the most crucial technologies for energy harvesting. High output charge density is fundamental for TENG to expand its application scope and accelerate industrialization; it depends on the dynamic equilibrium of charge generation, trapping, de-trapping, and migration within its core components. Here, this review classifies and summarizes innovative approaches to enhance the charge density of the charge generation, charge trapping, and charge collection layers. The milestone of high charge density TENG is reviewed based on material selection and innovative mechanisms. The state-of-the-art principles and techniques for generating high charge density and suppressing charge decay are discussed and highlighted in detail, and the distinct charge transport mechanisms, the technologies of advanced materials preparation, and the effective charge excitation strategy are emphatically introduced. Lastly, the bottleneck and future research priorities for boosting the output charge density are summarized. A summary of these cutting-edge developments intends to provide readers with a deep understanding of the future design of high-output TENG.

Carrier Generation and Recombination in AC-QLEDs with a Synergistic Capacitance Effect of ZnO/PVDF Heterofunction Layers.

The alternating current-driven electroluminescence (AC-EL) of Cd-based quantum dots is garnering increasing attention due to advantages such as high efficiency and an extended operating lifetime. However, the generation and transport mechanisms of charge carriers within devices still need to be more understood. Here, we construct a simple device and investigate its luminance mechanisms within a single cycle using time-resolved spectroscopy. We tested the luminance-voltage and luminance-frequency characteristics of the device as the thickness of the insulating layer varied, finding that they both exhibited a trend of initially increasing and then decreasing as the voltage or frequency increased. We subsequently investigated the transient electroluminescent characteristics of the device, which featured a P(VDF-TrFE-CFE) layer as the insulator. This layer prevents carrier injection from the Al electrode, while the ZnO layer acts as a charge-generating layer to provide additional carriers. We observed that with an increase in AC voltage, the strongest luminance peak is advanced in the cycle compared to when lower voltages were applied. The position of the strongest luminance peak is delayed with an increasing AC frequency. The C-V characteristics demonstrated that the synergistic P(VDF-TrFE-CFE)/ZnO exhibited a displacement current transforming to a conduct current, which activates the forward operation of the QLED and enables it to emit light. The mechanism we present may serve as a benchmark for improving the luminance and longevity of such devices.

The Rise of Tandem Perovskite Light-Emitting Diode.

In 2024, tandem perovskite light-emitting diodes (tandem-PLEDs) achieved a breakthrough external quantum efficiency of 43.42%, with an organic electroluminescence (EL) unit stacked atop a perovskite EL unit, surpassing the previous single-junction perovskite LEDs. This innovative design enables a higher brightness at lower currents, enhancing the longevity and efficiency of the tandem-PLEDs. Additionally, the tandem-PLEDs can also be fabricated by combining a perovskite EL unit with a perovskite quantum dot unit. In this perspective, the key advancements in tandem-PLEDs are highlighted, focusing on the development of perovskite-organic materials, perovskite-perovskite quantum dots, and the design principles for obtaining efficient and stable charge generation layers. But more importantly, the challenges and solutions are discussed in fabricating all-perovskite tandem LEDs using strongly polar solvents that have yet to be reported nowadays. This comprehensive guide aims to support researchers in advancing the practical deployment of tandem-PLED technology.

Charge generation layer with octylamine assistant layer for efficient tandem organic light-emitting diodes

Charge generation layer with octylamine assistant layer for efficient tandem organic light-emitting diodes

37‐4: Degradation Analysis on Li‐doped Organic Charge Generation Layer

Understanding degradation of charge generation layer (CGL) is uprising issue for efficient and stable tandem devices. Here, we explored how the electrical characteristics of Li‐doped CGL device change according to different stress conditions comprehensively and found out thermal stress affects more severely than electrical stress via capacitance‐voltage and temperature‐dependent current density‐voltage measurements. The exponential trap distribution model analysis and Poisson and drift‐diffusion simulation informed that the degradation of electrical properties is attributed to Li diffusion and actual thermal diffusion of Li was experimentally observed by XPS depth

77‐4: Highly Efficient Side‐by‐Side Three‐Stack Tandem Flexible OLED Displays with Yb‐doped n‐CGLs

We have succeeded in developing highly efficient side‐by‐side three‐stack tandem flexible OLED displays with Yb‐doped n‐type Charge Generation Layers (n‐CGLs), whose white current efficiency is up to 2.2 times as high as that of single OLED. The three‐stack tandem OLED display shows 1800 nits in full white with a polarizer. We found that the optimal combination of electron transporting material and metal as n‐CGL exhibits appropriate conductivities through EOD evaluation.

77‐2: Research on Suppressing the Electrical Crosstalk of Tandem OLED Sub‐pixels

Tandem OLED has attracted widely attention in display application due to its ability to reduce power consumption and increase lifetime simultaneously. The display industry is currently focusing on developing the structure and the process for tandem OLED. In the tandem OLED device, the common layer, including charge generation layer (CGL), will not only transport charge carriers vertically, but also transport the charge horizontally to adjacent sub‐pixels, resulting in electrical crosstalk. Moreover, the decrease of tandem OLED current will seriously affect the color gamut of display under low gray levels from 81.3% to 48.26%. Here, we provide theoretical simulation and some solutions to suppress the electrical crosstalk and optimize uniformity of tandem OLED display, providing some guidance for the development of tandem OLED technology.

Deterioration of Li-doped phenanthroline-based charge generation layer for tandem organic light-emitting diodes

Understanding the deterioration of the charge generation layer (CGL) is an uprising issue for efficient and stable tandem organic light-emitting diodes. Here, we comprehensively investigated the change in the electrical characteristics of Li-doped CGLs according to different stress conditions and compared the stability of Li diffusion in two phenanthroline-based electron transport materials. Through current density–voltage and capacitance-frequency measurements, it was revealed that electrical stress and thermal stress affect CGL’s electrical properties differently. Moreover, the exponential trap distribution model analysis informed that the Li diffusion is expedited toward narrowing depletion width in the CGL. Diffusion of Li and thermal effect to the diffusion was experimentally observed by X-ray photoelectron spectroscopy (XPS) depth profiling. We also evaluated variations in the operating voltage of tandem devices that differed only in nCGL. Overall, Li diffusion occurs more favorably in sparse Bphen film with weak binding energy rather than closely packed BPPB film with strong binding energy, which highlights that atomic geometry and morphological characteristics are crucial for the stability of tandem devices.

MoS2-based charge trapping layer enabled triboelectric nanogenerator with assistance of CNN-GRU model for intelligent perception

Self-powered sensing technology and smart perception technology have broad application prospects in flexible and wearable electronics. In this work, a flexible triboelectric nanogenerator (RMP-TENG) based on a room-temperature vulcanized silicone rubber (RTV)@(Molybdenum disulfide (MoS2)/Polyvinyl chloride (PVC)) functional layer is developed using a layer-by-layer self-assembly and material doping strategy. The RTV@(MoS2/PVC) functional layer is divided into a charge-generating layer (RTV/PVC) and a charge-trapping layer (RTV/MoS2). The synergistic effect of PVC and MoS2 has improved the surface roughness and charge transfer efficiency of RMP-TENG, doubling its output performance to 1055 V and 112 μA. In order to further improve the tactile sensing accuracy of RMP-TENG, a deep learning model based on Convolutional Neural Network (CNN) and Gated Recurrent Unit (GRU) is developed. It predicts the type of contact material based on the features of tactile signals, achieving a prediction accuracy of 93.975%. Additionally, by combining mobile smart terminals, the CNN-GRU model, and RMP-TENG, a wireless access control system based on self-powered tactile sensing and intelligent material recognition is developed. Through the optimization of these experiments and algorithms, RMP-TENG has achieved real-time material recognition capabilities. This demonstrates the broad application prospects of RMP-TENG in wearable energy supply, intelligent sensing, human-computer interaction, and other areas.

High-Performance Tandem Quantum-Dot Light-Emitting Diodes Based on Bulk-Heterojunction-Like Charge-Generation Layers.

In this study, the fundamental but previously overlooked factors of charge generation efficiency and light extraction efficiency (LEE) are explored and collaboratively optimized in tandem quantum-dot light-emitting diodes (QLEDs). By spontaneously forming a microstructured interface, a bulk-heterojunction-like charge-generation layer composed of a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)/ZnO bilayer is fabricated and an ideal charge-generation efficiency surpassing 115% is obtained. The coupling strength of the waveguide mode for the top unit and the plasmon polariton loss for the bottom unit are highly suppressed using precise thickness control, which increases the LEE of the tandem devices. The red tandem QLED achieves an exceptionally low turn-on voltage for electroluminescence at 4.0V and outstanding peak external quantum efficiency of 42.9%. The ultralow turn-on voltage originates from the sequential electroluminescence turn-on of the two emissive units of the tandem QLED. Benefiting from its unique electroluminescent features, an easily fabricated optical-electrical dual anti-counterfeiting display is built by combining a dichromatic tandem QLED with masking technology.

Impact of Varying Position and Ratio of Charge Generation Layer on Performance Parameters of Organic Photodiode

Organic photodiodes have emerged as the best alternative to inorganic devices during the last decade. Herein, a highly efficient organic photodiode having charge generation layer (CGL) is demonstrated. This charge generation layer is a combination of HAT-CN (hexaazatriphenylene-hexacarbonitrile) and TAPC (1,1-bis[(di-4-tolyamino)phenyl)]cyclohexane) materials which generate electrons and holes, correspondingly. Moreover, in this work, the proposed device (D2) is compared with other four non-CGL (D1) and CGL based (D3, D4 and D5) devices. In all the CGL based devices, positional variation of the CGL layer is incorporated. In the proposed device (D2), the CGL is situated outside the active layer in such a manner like HAT-CN is placed near acceptor and TAPC is near donor layer. In this way, the proposed device is showing the remarkable improvements in terms of photocurrent and dark current as 134.2 nA and 10.2 nA, respectively. The value of photocurrent of D2 is 34 times increased of the reference device (D1). Furthermore, on comparing with other CGL based devices D3, D4 and D5, photocurrent of D2 is approx 1.6, 1.4 and 9 times enhanced, correspondingly. Moreover, the thickness optimization and internal analysis of the proposed device are also performed to show the novelty of the presented work.

Charge generation layer with Yb assistant interlayer for tandem organic light-emitting diodes

Tandem organic light-emitting diode (OLED) devices require an efficient charge generation layer (CGL) between two stacked OLED units. In this study, a CGL with an Yb assistant interlayer was fabricated and investigated. The optical transmittance and charge generation performances of the CGLs were analyzed with respect to the Yb thickness. The best result was obtained at a Yb thickness of 3 nm, at which both the electrical and optical properties exhibited optimal performances. The optical transmittance was greater than 90 %; this was superior to the performances using Ag and Al interlayers. The insertion of a 3-nm Yb layer reduced the threshold voltage from 18 to 6 V. Capacitance measurements revealed that the insertion of the Yb layer enhanced charge generation in the CGLs, reducing the threshold voltage and enhancing charge transport. The tandem OLED device fabricated using Bphen:Liq/Yb/MoO3/TAPC as a CGL exhibited a 1.92 × enhancement in the current efficiency, which is nearly twice the ideal value, compared to a single-unit device. Thus, Yb is a promising candidate for use as an assistant interlayer in CGLs for high-performance tandem OLED devices.

A micro-dome array triboelectric nanogenerator with a nanocomposite dielectric enhancement layer for wearable pressure sensing and gait analysis.

The practical application of a triboelectric nanogenerator (TENG) as a self-powered sensor and an energy harvester is constrained by the need for a wide sensitivity range, significant output power, and structural flexibility. However, most research has focused on physical and chemical surface modifications of the charge-generating layer to enhance the TENG performance. Improving the charge storage ability could otherwise further enhance the overall performance. Here, we propose a flexible TENG design that incorporates a micro-dome array Ecoflex as the tribo-negative layer, coupled with a dielectric enhancement layer composed of a carbon black/Ecoflex composite. The addition of the CB/Eco composite layer to the micro-dome array triboelectric layer enhanced the output voltage performance by forming numerous micro capacitors within the dielectric layer. Furthermore, oxygen-containing fluorocarbon plasma treatment of the micro-dome array increased the surface energy, enhancing the interaction between the triboelectric layers. This leads to an enhancement in the output voltage and energy efficiency, exhibiting a power density of 197.4 mW m-2. The pressure sensitivity of the TENG was systematically investigated, demonstrating 2.57 V kPa-1 in the low-pressure range (0.612 to 8.58 kPa) and 1.70 V kPa-1 in the high-pressure range (8.58 to 20.83 kPa). Additionally, the encapsulated TENG sensor with spacers was integrated into insoles for self-powered gait analysis, providing real-time insights into walking patterns and frequencies. Exploring the TENG's energy harvesting capability revealed a peak-peak voltage of 89.4 V when two TENGs are connected in series. The comprehensive performance characterization of the TENG demonstrates its promising applications in wearable, self-powered sensing, and energy harvesting systems.

Effects of charge generation layers on multiple guest/host bilayer-based tandem OLEDs

Compared to OLEDs with a guest/host system as the light emitting layer (EML), in which guest molecules are doped or mixed into the host molecule layer, those with multiple guest/host bilayers as the EML has the advantage of uniform distribution of guest-to-host molecule ratio throughout the entire emission layer thickness. Herein, we report on the tandem OLED based on multiple guest/host bilayers as the EML, and the effects of charge generation layers (CGL) on device performance for the first time. With four pairs of vacuum evaporated host of 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl (CBP) and guest of bis(1-phenylisoquinoline) (acetylacetonate) iridium(III) (Ir(piq)2(acac)) as the EML, two types of tandem OLEDs with 8-Hydroxyquinolinolato-lithium (Liq)/MoO3 or Liq/2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (HAT-CN) bilayer as the charge generation layer, respectively, were investigated. The results showed that the device with Liq/MoO3 as CGL (T1) exhibited higher current efficiency but lower power efficiency than the one with Liq/HAT-CN as the CGL (T2). Single carrier devices with either Liq/MoO3 or Liq/HAT-CN as the charge injection layer were fabricated to investigated charge injection ability of the CGLs. The results show that Liq/MoO3 CGL exhibit both lower electron and hole injection ability than Liq/HAT-CN, which is the origin of higher turn-on volage and lower power efficiency of T1 than T2. However, the balance degree of electron and hole injection of Liq/MoO3 is better than Liq/HAT-CN, resulting higher current efficiency of T1 than T2. These results provide a novel strategy towards fabricating high performance tandem OLEDs.

Blue emitting exciplex for yellow and white organic light-emitting diodes

White organic light-emitting diodes (WOLEDs) have several desirable features, but their commercialization is hindered by the poor stability of blue light emitters and high production costs due to complicated device structures. Herein, we investigate a standard blue emitting hole transporting material (HTM) N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidine (NPB) and its exciplex emission upon combining with a suitable electron transporting material (ETM), 3-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole (TAZ). Blue and yellow OLEDs with simple device structures are developed by using a blend layer, NPB:TAZ, as a blue emitter as well as a host for yellow phosphorescent dopant iridium (III) bis(4-phenylthieno[3,2-c]pyridinato-N,C2')acetylacetonate (PO-01). Strategic device design then exploits the ambipolar charge transport properties of tetracene as a spacer layer to connect these blue and yellow emitting units. The tetracene-linked device demonstrates more promising results compared to those using a conventional charge generation layer (CGL). Judicious choice of the spacer prevents exciton diffusion from the blue emitter unit, yet facilitates charge carrier transport to the yellow emitter unit to enable additional exciplex formation. This complementary behavior of the spacer improves the blue emission properties concomitantly yielding reasonable yellow emission. The overall white light emission properties are enhanced, achieving CIE coordinates (0.36, 0.39) and color temperature (4643 K) similar to daylight. Employing intermolecular exciplex emission in OLEDs simplifies the device architecture via its dual functionality as a host and as an emitter.Graphical abstract

Highly efficient tandem organic light-emitting diodes using p-type metal halide copper iodide (CuI)

Efficient charge generation is essential for tandem organic light-emitting diode (OLED) devices. In this study, we introduce a p-type copper iodide (CuI) layer within the charge generation layer (CGL) that exhibits high charge generation efficiency in tandem OLED devices. Briefly, CuI is deposited as a thin layer via thermal evaporation technique. X-ray diffraction (XRD) analysis reveals the formation of γ-CuI, and the ultraviolet-visible (UV-Vis) spectral analysis demonstrates outstanding optical transparency (∼95%) of the deposited CuI films in the visible range. The current-voltage (I-V) and capacitance-voltage (C-V) analyses show that the p-type CuI layer is a vital and excellent charge generator and enhances the current density significantly. The tandem OLED device fabricated using Bphen:Liq/CuI/HAT-CN as the CGL results in a substantial 1.9-fold increase in current efficiency compared to the single-unit OLED device, approaching the theoretical two-fold increase. These findings highlight the potential of CuI as a promising p-type material for CGL design in tandem OLED devices.

Largely improving the lifetime by inserting a Yb metal layer into the charge generation layer in tandem organic light-emitting diodes

Largely improving the lifetime by inserting a Yb metal layer into the charge generation layer in tandem organic light-emitting diodes

Characteristic performance and analysis of the positional variation of the charge generation layer to enhance the performance of OLEDs

Characteristic performance and analysis of the positional variation of the charge generation layer to enhance the performance of OLEDs

An In-Depth Analysis of Variation in Characteristic Performance of OLED with Respect to Position of Charge Generation Layer

In this paper, a high performance blue organic light emitting diode having a charge generation layer (CGL) is proposed and compared with the other five CGL and non-CGL based devices. The utilized CGL layer in the different structure consists of two materials; HAT-CN (hexaazatriphenylene-hexacarbonitrile) and TAPC (1,1-bis[(di-4-tolyamino)phenyl)]cyclohexane,) for electrons and holes generation, correspondingly. In the proposed novel structure, the CGL layer is incorporated outside of the emissive layer (EML) which significantly enhances the device performance in terms of current and luminescence. The device exhibits luminescence and current values as 3636.3 cd m−2 and 0.44 A, respectively. Furthermore, this paper represents in-depth internal analysis of the six devices (D1-D6). This analysis is provided by drawing horizontal and vertical cutlines inside the devices. The proposed device is analysed and compared with other mentioned devices in terms of several parameters such as Langevin recombination rate, electron concentration, hole concentration, band energy, total current density, electron affinity, hole QFL (quasi-Fermi level), conduction current density, potential distribution and electron/hole mobility. In comparison with D1, D2, D3, D4 and D5, the current of the proposed device (D6) is about 16.9, 2.2, 1.7, 3 and 1.6 times improved, correspondingly. Moreover, structural analysis is also included to understand the performance of the devices more precisely.

Semi-Transparent, Pixel-Free Upconversion Goggles with Dual Audio-Visual Communication.

The intractable brittleness and opacity of the crystalline semiconductor restrict the prospect of developing low-cost imaging systems. Here, infrared visualization technologies are established with large-area, semi-transparent organic upconversion devices that bring high-resolution invisible images into sight without photolithography. To exploit all photoinduced charge carriers, a monolithic device structure is proposed built on the infrared-selective, single-component charge generation layer of chloroaluminum phthalocyanine (ClAlPc) coupled to two visible light-emitting layers manipulated with unipolar charges. Transient pump-probe spectroscopy reveals that the ClAlPc-based device exhibits an efficient charge dissociation process under forward bias. This process is indicated by the prompt and strong features of electroabsorption screening. Furthermore, by imposing the electric field, the ultrafast excited state dynamic suggests a prolonged charge carrier lifetime from the ClAlPc, which facilitates the charge utilization for upconversion luminance. For the first time, >30% of the infrared photons are utilized without photomultiplication strategies owing to the trivial spectrum overlap between ClAlPc and the emitter. In addition, the device can broadcast the acoustic signal by synchronizing the device frequency with the light source, which enables to operate it in dual audio-visual mode. The work demonstrates the potential of upconversion devices for affordable infrared imaging in wearable electronics.