Simple Device Structure Research Articles

Reducing energy loss via adjusting the anode work function and perovskite layer morphology for the efficient and stable hole transporting layer-free perovskite solar cells

Hole transporting layer-free perovskite solar cells (HTL-free PVSCs) have great potential in the commercialization process due to their simple device structure and low processing temperature. However, the photovoltaic performance of the HTL-free PVSCs is limited by severe carrier recombination and energy loss (Eloss) caused by the large energy level mismatching at the ITO/MAPbI3 interface. In this work, we introduce three dipole interlayers, including 4-Fluorophenylacetic acid, 4-(Trifluoromethyl) phenylacetic acid, and 3,5-Bis(trifluoromethyl)phenylacetic acid, to tune the surface work function (WF) of the ITO substrates by forming interfacial dipoles and shifting the Fermi level of the ITO substrates. The carboxyl groups of these dipole interlayers can passivate the surface terminal –OH groups on the ITO surface. The optimized energy level alignment and reduced defect states at the ITO/MAPbI3 interface are beneficial to suppressing the carrier recombination and Eloss at the ITO/MAPbI3 interface. Besides, the dipole interlayers change the wettability of the ITO substrates and facilitate the formation of high-quality and fewer trap state perovskite films. The dipole interlayers modified HTL-free PVSCs achieve the highest power conversion efficiency (PCE) of 20.19%, which is higher than the pristine PVSCs with the highest PCE of 14.94%. The dipole interlayers modified flexible and large area HTL-free PVSCs also exhibit enhanced PCE compared with the pristine PVSCs. Besides, the stability of the dipole interlayer modified PVSCs is better than the pristine PVSCs. This work provides an in-depth study on the Eloss at the ITO/MAPbI3 interface and promotes the fabrication of efficient and stable HTL-free PVSCs.

Low power multilevel resistive switching in titanium oxide-based RRAM devices by interface engineering

The stochastic nature of conductive filament formation and dissolution always leads to large fluctuations of key device parameters that hinder the practical applications of resistive random-access memories (RRAMs). Here, we report a simple bilayer oxide-based device structure of Al/TiOx/TiOy/FTO (x < y) employed to address this variability issue and improve the overall performance of the memory device. The bipolar resistive switching performance remarkably improved in these bilayer devices with lower forming voltage (~1 V), set/reset voltages of 0.4/-0.6 V, a programming current of 10 μA, an enlarged ON/OFF ratio (>103), longer retention (>103 s), and better uniformity as compared to the control Al/TiOy/FTO device. Moreover, the modulation of TiOx layer thickness enables tunability of switching voltages, currents, and the resistance window. In addition, reliable and reproducible multiple resistance states, more specifically different low resistance states, can be achieved in bilayer devices by controlling the programming current down to 10 μA, which is in contrast to the binary states of the control devices. These improved switching parameters with multilevel storage capability in bilayer devices are attributed to the incorporation of an oxygen vacancy-rich interfacial layer, namely TiOx, which serves as an oxygen vacancy reservoir and facilitates effective conductive filament formation inside the switching layer. Furthermore, the thermodynamics involving the dielectric constant and Gibb's free energy of oxide formation at the Al/TiOx and TiOx/TiOy interfaces play a pivotal role in the associated switching mechanism. The spatial variability of the operating voltage across these devices is found to be as low as 8%. These findings pave the way for low power, low cost, and high density data storage applications.

Fast and efficient germanium quantum dot photodetector with an ultrathin active layer

An ultrathin layer (13 nm) of germanium (Ge) quantum dots embedded in a SiO2 matrix was deposited on a Ge substrate for photodetection in both the visible and near-infrared (IR). Operated at T = 150 K, the device exhibits higher than 105% internal quantum efficiency (IQE) at a reverse bias of −1.3 V under low light conditions (&amp;lt;30 nW) at both λ= 640 and 1550 nm. The transient response of 640 nm pulses stays below 15 ns for both rise and fall times; the IR response is only slightly slower. Our work demonstrates a high-performance broadband photodetector with high IQE and fast response in a simple silicon technology-compatible device structure.

Highly sensitive self-powered pressure and strain sensor based on crumpled MXene film for wireless human motion detection

Recently, pressure/strain sensor based on triboelectric nanogenerator (TENG) has gained great attentions for monitoring daily health status and robotic research fields, because of their simple device structures and self-powered feature. However, higher sensitivity and stretchability are still demanded for satisfying the practical applications. In this work, a self-powered pressure and strain sensor was achieved by utilizing crumpled MXene film as the single-electrode mode TENG. Benefiting from the reconfigurable behavior of the crumpled structure, the MXene TENG showed a maximum areal strain and linear tensile ratio of 2150% and 400%, respectively. Meanwhile, because of the enlarged contact area between triboelectric layers, the output power density of the MXene TENG with micro-crumples was highly improved by 36 times. Therefore, the as prepared sensor exhibited excellent sensitivity of 2.35 V kPa−1 under pressures from 0.3 to 1.0 kPa, which is superior to majority of the reported sensors based on tribo-/piezo- electricity. In addition, the sensor can be easily attached to human joints to capture and collect the complicated movement signals. By combining with Bluetooth transmission technology, wireless real-time monitoring was realized through transmitting human movement signals to a mobile phone App.

Preparation of low-cost perovskite solar cells with high-quality perovskite films in an ambient atmosphere

High-quality perovskite films are extremely crucial to obtain perovskite solar cells with excellent photovoltaic performance, especially for carbon-based hole transport materials (HTM)-free perovskite solar cells. In this work, a facile and low-cost double two-step method (DT-method) is developed to prepare uniform and pinhole-free CH3NH3PbI3 perovskite films in an ambient atmosphere by utilizing the dissolution-recrystallization of PbI2 in DMF. That is to spin-coat PbI2 and CH3NH3I solution sequentially onto pristine perovskite films prepared by the conventional two-step method. The solar cells fabricated by the DT-method show a dramatic performance improvement, including V oc, J sc, and fill factor reach 0.85 V, 15.56 mA cm−2, and 0.58 respectively, which increase power conversion efficiency from 3.93% to 7.58% compared with the conventional two-step method. The improvement in performance and stability of solar cells is mainly due to the higher coverage of perovskite films onto the underlying mesoporous TiO2 layer and a negligible amount of PbI2 residue, which can effectively reduce charge recombination and promote the rapid transfer of charge carriers. In summary, this work presents a process for preparing carbon-based HTM-free perovskite solar cells (PSCs) in a high-humidity atmospheric environment (60%–85%). This simple device structure and preparation condition can greatly reduce the production threshold and cost of PSCs.

Crossbar Array of Artificial Synapses Based on Ferroelectric Diodes

AbstractTwo terminal devices that exhibit resistance switching in response to an external voltage are interesting for neuromorphic computing applications. Owing to its simple device structure, a crossbar array of two‐terminal resistance switching devices is highly desired for application as artificial neural network weights. Here, ferroelectric diodes that show resistance switching in their forward bias are presented. The resistance can be set to a high‐ and a low‐resistance state or any state between these limits. It is demonstrated that the ferroelectric diodes can function as an artificial synapse. An array of the ferroelectric diodes with two bit and two row lines (2 × 2) is demonstrated. The resistance of every bit is independently tuned, and spike‐time‐dependent plasticity is shown for the array.

Highly efficient solution-processed white OLEDs via TADF host-sensitized dinuclear platinum (III) complex

External quantum efficiency (EQE), color rendering index (CRI), color correlated temperature (CCT), and spectral stability are key challenges for constructing high-performance white organic light-emitting diodes (WOLEDs) with a simple device structure. Herein, in order to resolve these issues, we primarily employed a thermally activated delayed fluorescence (TADF) emitter of CzAcSF as a host emitter and a dinuclear platinum (III) complex (Pt-1) as a guest emitter to construct solution-processed single-emitting layer WOLEDs at low guest concentrations of 0.75–1.50 wt. %. Thanks to their broad coverage of visible spectra, efficient energy transfer, and weak charge trap of Pt-1, the optimized WOLEDs showed an increasing EQE of 11.93% and a current efficiency of 30.76 cd/A with a high CRI of 75 and a CCT of 5210 K. Furthermore, the stable electroluminescent spectra with CIE (commission internationale de L'Eclairage) coordinate deviations of Δx = 0.022 and Δy = 0.015 were exhibited. This is an outstanding example for high-performance WOLEDs via employing a TADF host-sensitized low-concentration dinuclear platinum (III) complex simultaneously with high efficiency, CRI, CCT, and color stability.

Simple and green route for fabrication of a nanostructured of the graphene‐Fe3O4@PANI for the photovoltaic activity

In this work, for the first time, Gr (graphene)|Fe3O4@PANI nanocomposite was synthesized from graphite, aniline-HCl and FeCl3.6H2O via a simple in-situ and green route as the active layer for photovoltaic application. The proposed nanocomposite was characterized by FT-IR, SEM, TEM, UV-vis spectroscopy, XRD technique, and then the thermal, magnetic, electrochemical, and photovoltaic properties investigated. The energy gap was calculated, and it is noticed that the optical band gap of nanocomposite fallows an indirect transition, arising from a strong spin-orbit coupling created by Fe3O4 in the Gr|Fe3O4@PANI nanocomposite. Next, polymer solar cell (PSC) based on this nanocomposite was fabricated with a simple device structure of FTO│TiO2│Gr|Fe3O4@PANI│Al. The photovoltaic properties of the cells have been evaluated under AM 1.5G illumination at 60 mW/cm2 with a solar simulator. A power conversion efficiency (PCE) of 1.81% was observed with a short circuit current (Jsc) of 4.14 mA/cm2, an open-circuit voltage (Voc) of 0.71 V, which indicates this kind of conjugated polymer should be a promising material in the application of polymer solar cells.

Efficient Perovskite White Light-Emitting Diode Based on an Interfacial Charge-Confinement Structure.

Perovskite light-emitting diodes (LEDs) show great potential for next-generation lighting and display technology. Despite intensive studies on single-color devices, there are few reports on perovskite-based white LEDs (Pe-WLEDs). Here, an efficient Pe-WLED based on a blue perovskite and an orange phosphorescent emitter is reported for the first time. It is found that using a simple perovskite/phosphor bilayer emitting structure, there is inefficient energy transfer from the blue perovskite to the orange phosphor, leading to low efficiency and a significant color shift with driving voltage. We address this issue by introducing a quantum-well-like charge-confinement structure for enhancing carrier trapping and thus exciton formation in the phosphorescent emitter. As a result, a high external quantum efficiency of 10.81% is obtained. More interestingly, by tuning the dopant concentration of the phosphorescent emitter using this simple device structure, we can controllably get Pe-WLEDs with very stable white light for display applications or tunable color from warm white to daylight for lighting applications.

Highly Birefringent Microfiber Hybrid Interferometer Sensor

In this work, an optical microfiber-based hybrid interferometer is presented. A combination of two types of in-line interferometers is achieved by inserting a section of nonadiabatic tapered polarization maintaining microfiber into a Lyot filter. The hybrid interference spectrum shown as large spectrum envelope and fine fringes, corresponding to the polarized and modal interferences is obtained. We experimentally investigate the response characteristics of the two-interference system using both spectral interrogation and spatial frequency domain analysis. The refractive index sensitivities are 1150.0nm/RIU and 1779.8nm/RIU, and the temperature sensitivities are 190pm/°C and -12.7 pm/°C for two interferences, respectively. The proposed hybrid interferometer has the advantages of simple device and compact structure, and has the potential of simultaneous measurement of multiple parameters.

38.4: Invited Paper: Stack Design of OLEDs with High Performance and Simplified Device Structures

The increasingly complex layer structure of commercial OLEDs leads to higher manufacturing costs. In this paper, we demonstrate a simplified device structure with only two layers between the anode and the emissive layer, compared to the usual three or four layers in state‐of‐the‐art devices. The stack is designed so as to ensure efficient hole injection and transport. As a result, the devices achieved longer lifetime than the more complex structure, while maintaining equivalent chromaticity, efficiency and operating voltage. Fewer layers help realize cost‐effective mass production.

In-plane micro-supercapacitor using polymer nanosheet assembly as a weak acid solid electrolyte

In-plane micro-supercapacitors, in which the electrodes are arranged on the same plane have attracted much attention because of their light weight, simple device structure, etc. In this paper, micro-supercapacitors were fabricated by using polymer nanosheet multilayer film as a solid electrolyte. The micro-supercapacitors were fabricated by sequential deposition poly(N-dodecyl acrylamide-co-acrylic acid) monolayer onto a solid substrate with interdigitated gold electrodes. The capacitor characteristics were investigated by cyclic voltammetry under saturated humidity condition. It was revealed that the micro-supercapacitor showed a capacitance of 33 µF/cm2.

Microstructure Engineering of Stretchable Resistive Strain Sensors with Discrimination Capabilities in Transverse and Longitudinal Directions

AbstractFeaturing simple device structure, high sensitivity, and excellent reliability, stretchable resistive sensors have developed rapidly due to the high demand for flexible and wearable electronics. Nevertheless, it remains critically challenging to evaluate external stimuli using one simple device for diverse application scenarios. Here, a microstructure is engineered for a stretchable sensor by a facile replication/transferring and a prestretching/releasing process, enabling the device to have discrimination capabilities in the transverse direction (X‐axis) and longitudinal direction (Y‐axis). Consisting of silver nanowires (Ag NWs)/transition metal carbides (MXene)/poly(3,4‐ethylenedioxythiophene):poly (styrene‐sulfonate) (PEDOT:PSS) conducting layer and polydimethylsiloxane (PDMS)/Ecoflex elastomer, the microstructured sensor has a broad strain range of 120% along the X‐axis and a large gauge factor (GF) of 37.44 along the Y‐axis, and shows good stability during 1000 stretching/releasing cycles along two directions, indicating the excellent interfacial connection between the sensing layer and elastomer. As a result, taking advantages of distinct performance along two directions, the proposed stretchable sensor is demonstrated to monitor a variety of human movements and physical stimuli as a wearable and flexible device, revealing its promising potential in diverse application scenarios.

Demonstration of electronic devices in graphitic carbon nitride crystalline film

Graphitic carbon nitride (g-C3N4) exhibits semiconducting properties and is a promising candidate for use as a metal-free functional material. Electronic transport in g-C3N4 depends on the crystal orientation, resulting in the anisotropic characteristics of low out-of-plane and high in-plane resistivity. We investigated a Schottky barrier diode (SBD) and a heterojunction diode (HJD) with out-of-plane transport properties and a top-gate device with in-plane transport properties. The SBD with a Cr/Au Schottky contact exhibited rectifying behavior with a turn-on voltage of ∼1.0 V and estimated series resistance and barrier height at the interface of 1.63 kΩ and 344 meV, respectively. The HJD comprises a g-C3N4 film and an n-type hexagonal silicon carbide (4H–SiC) substrate, with a turn-on voltage of 4.0 eV. The HJD belonged to a type-II band alignment with a staggered-gap; it had a thin insulator-based van der Waals gap at the interface, thereby inducing tunneling transport. In-plane carrier transport control was carried out by the top-gate device with a Parylene-C film gate dielectric and was achieved only when the negative bias voltage was applied along the out-of-plane direction, indicating the realization of the normally off switch that utilizes the intrinsic transport characteristics and a simple device structure.

Research on local compensation technology of large diameter steel pipe with heterogeneous structure and analysis of application

When large-diameter steel pipes have special structures with stiffening rings, grouting holes, etc., the electrostatic spray epoxy powder anti-corrosion process is likely to produce large temperature differences due to the sudden thickness changes during heating, which cannot meet the temperature requirements of powder spraying. This paper designs a set of automatic temperature compensation technology for large-diameter steel pipes with stiffening rings and grouting holes, which aims to solve the problem of uneven heating of stiffening rings and grouting holes in the medium frequency induction heating powder spraying process. Through the method of “intermediate frequency heating + stiffening ring temperature compensation”, the inner and outer parts of the steel pipe are heated evenly and the temperature difference is reduced. The temperature difference between the inner wall of the steel pipe is reduced to 3∼15°C in the area of the stiffening ring, and the temperature is reduced in the area of the grouting hole. The difference is reduced from 70°C to 57°C to 20°C, the temperature difference is controlled within the allowable range of technical requirements, and the temperature compensation effect is good. The process has the advantages of simple device structure, high work efficiency, and small temperature difference in the spraying area, and is suitable for use on similar large-diameter steel pipes or other hydraulic metal structures.

Slot‐Die Coating of All Organic/Polymer Layers for Large‐Area Flexible OLEDs: Improved Device Performance with Interlayer Modification

AbstractOrganic light‐emitting diodes (OLEDs) fabricated on flexible transparent substrates have found application in displays, lighting, and signage. Optimization of the fabrication procedures is critical for commercialization to maximize performance and reduce costs. Utilization of the slot‐die coating technique, a solution‐processing roll‐to‐roll method, has emerged as a viable method to manufacture flexible OLED devices. Here, the fabrication of flexible OLEDs via the slot‐die coating technique under ambient condition is reported. The OLEDs have a simple architecture of polyethylene terephthalate (PET)/indium–tin oxide (ITO)/hole injection layer (HIL)/emissive layer (EML)/electron injection layer (EIL)/Ag, where poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is used as the HIL, Super Yellow (SY, poly(1,4‐phenylenevinylene) copolymer) is used as the EML, and poly((9,9‐bis(3′‐(N,N‐dimethylamino)propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)) (PFN) is used as the EIL. The optimization of the PFN layer using slot‐die coating technique is focused by varying solvent, solvent additives, substrate temperature, and coating speeds. The OLEDs that have PFN layers processed with the known solvent additives, 1,8‐diiodooctane (DIO) or diphenyl ether (DPE), show a performance increase compared to OLEDs based on PFN layers processed with no solvent additives. Finally, large‐area multicolor OLEDs are constructed with organic/polymer layers being slot‐die coated in sequence, of which all display homogeneous luminance under bending/folding conditions, highlighting the potential of this simple device structure and processing method.

Direct Observation of Photoexcited Electron Dynamics in Organic Solids Exhibiting Thermally Activated Delayed Fluorescence via Time‐Resolved Photoelectron Emission Microscopy

AbstractSolid‐state films exhibiting thermally activated delayed fluorescence (TADF) can offer high internal electroluminescence (EL) quantum efficiency, even in a simplified device structure. However, the exciton dynamics in solid‐state TADF films, particularly for the unexpected exciton loss processes such as concentration quenching, have not yet been clarified. The dynamics of photoexcited electrons in the TADF process of a 2,4,5,6‐Tetra (9H‐carbazol‐9‐yl) isophthalonitrile (4CzIPN) solid film are observed via time‐resolved photoelectron emission microscopy (TR‐PEEM) and the results are compared with the conventional time‐resolved photoluminescence (TR‐PL) technique. The initial decay process of the photoexcited electrons probed via TR‐PEEM is thoroughly traced in the TR‐PL signal, while unusual long‐lived electrons are detected only through the use of TR‐PEEM. These results indicate that the excitons of 4CzIPN spontaneously dissociate into free carriers within the exciton lifetime, which seems to be a common process that contributes to the exciton loss in polar organic solids.

3D Triptycene‐Fused Acridine Electron Donor Enables High‐Efficiency Nondoped Thermally Activated Delayed Fluorescent OLEDs

AbstractOrganic light‐emitting diodes (OLEDs) with simple nondoped device structure are extremely attractive for real applications since excitons can be utilized without considering the possible charge trapping and morphology issues in the host–dopant systems. Emitters with suppressed concentration annihilation capability are essential for nondoped devices. Herein, two thermally activated delayed fluorescence (TADF) emitters based on a novel 3D electron donor, namely, TDMAC, are constructed. The TDMAC donor consists of a conventional donor with fused triptycene scaffold. Benefitting from the unique rigid and bulky triptycene moiety, these TADF emitters exhibit excellent thermal, morphological, and photophysical properties. Consequently, highly efficient OLEDs with external quantum efficiencies up to 24.2% and 23% are realized for doped and nondoped devices, respectively.

Unravelling the electron injection/transport mechanism in organic light-emitting diodes

Although significant progress has been made in the development of light-emitting materials for organic light-emitting diodes along with the elucidation of emission mechanisms, the electron injection/transport mechanism remains unclear, and the materials used for electron injection/transport have been basically unchanged for more than 20 years. Here, we unravelled the electron injection/transport mechanism by tuning the work function near the cathode to about 2.0 eV using a superbase. This extremely low-work function cathode allows direct electron injection into various materials, and it was found that organic materials can transport electrons independently of their molecular structure. On the basis of these findings, we have realised a simply structured blue organic light-emitting diode with an operational lifetime of more than 1,000,000 hours. Unravelling the electron injection/transport mechanism, as reported in this paper, not only greatly increases the choice of materials to be used for devices, but also allows simple device structures.

TID Effects Induced by ARACOR, 60Co, and ORIATRON Photon Sources in MOS Devices: Impact of Geometry and Materials

Total ionizing dose (TID) effects induced by different photon sources are studied in MOS devices. The dose factor (DF), defined as the ratio between dose deposition in dosimeter and actual dose deposition in MOS-sensitive oxides (SOs), is estimated using Monte-Carlo simulations of energetic photons striking simple device structures. An effective TID approach is proposed to account for both the real ionizing dose depositions in small volumes and the charge yield. This method is applied to a silicon-on-insulator (SOI) technology using three photon sources: the usual ARACOR and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sup> Co sources, which deliver several tens of kiloelectron volt photons and ~1.25-MeV photons, respectively, and a third facility named ORIATRON, a 6-MeV electron linear accelerator that produces photons on a wide energy spectrum. This topic, investigated intensively in the literature a few decades ago, is revisited in the context of several evolutions including: new radiation sources, novel simulation tools, and device scaling, which all impact ionizing dose deposition in microsensitive volumes of current electronic technologies. Dedicated numerical simulations demonstrate the importance of taking into account the entire stack of materials in order to get the most accurate estimations of TID in the SO. Descriptions of the back-end-of-line (BEOL) layers (especially when the technology uses copper), the polysilicon gate, the Buried OXide (BOX) (for SOI devices), but also of the substrate and package are mandatory in these simulations, since dose enhancement and/or backscattered photons can be a significant source of TID variation in the gate oxide. Also the package lid composition and its thickness can be major TID contributors. The results show that the use of a prefilter with lead and aluminum can optimize ionizing dose deposition