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Top electrodes of organic photovoltaics (OPVs) are usually thermally evaporated in the vacuum, which is non‐continuous and time‐consuming and has been the bottleneck for the OPV fabrication process. Printable top electrodes that are free of vacuum, high temperature, and solvents will make OPVs more attractive. Low‐melting‐point alloys (LMPAs) are promising candidates for printable OPV electrodes thanks to the merits of matching work functions, high electron conductivity, high environment stability, and no need for post‐treatment. Here, LMPA electrodes are directly deposited on OPVs by simply falling a single LMPA droplet onto the substrate. The LMPA droplet spreads to form a thin film with a smooth interface intimately contacting the substrate. The electrode area can be tailored by adjusting the droplet diameter or the Weber number, which is the ratio of inertia to surface tension. The interface morphology is mainly affected by the contact temperature. The degree of oxidation and charges on the droplet can also influence the electrode area and interface morphology. OPVs with droplet‐impacted LMPA electrodes exhibit power conversion efficiencies of up to 16.17%. This work demonstrates the potential of single‐droplet impact deposition as a simple method for printing OPV electrodes for scalable manufacturing. [ABSTRACT FROM AUTHOR]

Abstract Hafnium‐oxide‐based ferroelectrics have garnered considerable research interest, primarily for their robust ferroelectricity at the nanoscale and their high compatibility with complementary metal‐oxide‐semiconductors processes. However, the impact of electrodes on the ferroelectric properties of hafnium‐oxide layer, particularly that of top electrodes, is not yet fully understood even in the simplest capacitor geometry. In this study, the La0.67Sr0.33MnO3/Hf0.5Zr0.5O2 (LSMO/HZO) epitaxial heterostructure is utilized as a model system to conduct a systematic comparative study on ferroelectricity between the LSMO/HZO (H‐LS) bilayer and LSMO/HZO/LSMO (LS‐H‐LS) trilayer samples. In comparison to the H‐LS sample, the LS‐H‐LS sample exhibits a more uniform polar domain configuration and larger ferroelectric polarization. Moreover, the LS‐H‐LS sample exhibits significant improvements in leakage, endurance, and retention. These substantial enhancements in ferroelectricity are likely due to interfacial stress imposed by the LSMO capping layer and its capacity to accommodate extra oxygen vacancies. These results underscore the pivotal role of oxide‐based top electrodes in determining the ferroelectricity of hafnium‐oxide‐based heterostructures, providing crucial insights for optimizing the performance of innovative ferroelectric devices.

Herein, sol–gel-processed Y2O3 resistive random-access memory (RRAM) devices were fabricated. The top electrodes (TEs), such as Ag or Cu, affect the electrical characteristics of the Y2O3 RRAM devices. The oxidation process, mobile ion migration speed, and reduction process all impact the conductive filament formation of the indium–tin–oxide (ITO)/Y2O3/Ag and ITO/Y2O3/Cu RRAM devices. Between Ag and Cu, Cu can easily be oxidized due to its standard redox potential values. However, the conductive filament is easily formed using Ag TEs. After triggering the oxidation process, the formed Ag mobile metal ions can migrate faster inside Y2O3 active channel materials when compared to the formed Cu mobile metal ions. The fast migration inside the Y2O3 active channel materials successfully reduces the SET voltage and improves the number of programming–erasing cycles, i.e., endurance, which is one of the nonvolatile memory parameters. These results elucidate the importance of the electrochemical properties of TEs, providing a deeper understanding of how these factors influence the resistive switching characteristics of metal oxide-based atomic switches and conductive-metal-bridge-filament-based cells. [ABSTRACT FROM AUTHOR]

Over the past decade, perovskite solar cells (PSCs) have achieved significant achievements. But the golden triangle problem of commercial development, which encompasses high efficiency, high stability, and low cost, remains unresolved. Carbon materials exhibit a diverse range of morphological structures and possess numerous advantages. They are extensively used in PSCs to overcome the challenges encountered during PSCs commercialization. The PSCs utilizing graphene as the top electrodes not only deliver an impressive efficiency of 22.8%, but also show exceptional long‐term stability. The PSCs using carbon nanotubes as transparent conductive electrodes obtain an efficiency of 19%, exhibiting significant potential for scalable applications. Herein, the advantages of carbon materials as conductive electrodes are overviewed. The compatibility of carbon materials as conductive electrodes in PSCs, along with the associated challenges, regulatory strategies, and device performance are systematically discussed in terms of their intrinsic characteristics. The application of carbon materials derived from petroleum by‐products and biomass in the top electrodes of PSCs are summarized in detail. Finally, the underlying reasons why PSCs using carbon electrode show a comparatively lower efficiency when compared to conventional devices is analyzed in‐depth. The potential research directions are proposed to promote the development of carbon conductive electrodes in PSCs. [ABSTRACT FROM AUTHOR]

Organic electrochemical transistors (OECTs) have garnered significant interest due to their ability to facilitate both ionic and electronic transport. A large proportion of research efforts thus far have focused on investigating high-performance materials that can serve as mixed ion doping and charge transport layers. However, relatively less attention has been given to the gate-electrode materials, which play a critical role in controlling operational voltage, redox processes, and stability, especially in the context of semiconductor-based OECTs working in accumulation mode. Moreover, the demand for planarity and flexibility in modern bioelectronic devices presents significant challenges for the commonly used Ag/AgCl electrodes in OECTs. Herein, we report the construction of high-performance accumulation-mode OECTs by utilizing a gate electrode made of three-dimensional (3D)-printed graphene oxide. The 3D-printed graphene oxide electrode incorporating one-dimensional (1D) carbon nanotubes, is directly printed using an aqueous-based ink and showcases exceptional mechanical flexibility and porosity properties, enabling high-throughput preparation for both top gates and integrated planar architecture, as well as fast ion/charge transport. OECTs with high performance comparable to that of Ag/AgCl-gated OECTs are thus achieved and present promising feasibility for electrocardiograph (ECG) signal recording. This provides a promising choice for the application of flexible bioelectronics in medical care and neurological recording. [ABSTRACT FROM AUTHOR]

All printing of organic photovoltaics (OPVs) including the top electrode is highly desirable for achieving cost‐effective, high‐throughput, and large‐area photovoltaic manufacturing. Here, the printing of a low‐melting‐point alloy as top electrodes in OPVs via blade coating is investigated. The Field's metal (FM) with the melting point of 62 °C is adopted for the top electrodes, because FM can be printed under moderate temperatures without harming the active layers while remaining solid state under solar irradiation. The correlations between the processing parameters and properties of the blade‐coated electrodes are elucidated. OPVs based on the D18:Y6 active layer and blade‐coated FM electrodes achieve a highest power conversion efficiency of 17.28%. The OPVs with FM‐electrode demonstrate much higher thermal stability than that of the Ag‐electrode devices. All‐printed OPVs, in which the FM electrode is blade coated and the other layers are prepared by flexible micro‐comb printing, exhibit an efficiency of 16.07%. The results represent the records of evaporation‐free and all‐printed OPVs, demonstrating that printing FM as OPV electrodes is a cost‐effective and time‐saving strategy to substitute the vacuum‐evaporated metals, as well as a feasible route toward high‐performance all‐printed OPVs. [ABSTRACT FROM AUTHOR]

Herein, sol–gel-processed Y2O3 resistive random-access memory (RRAM) devices were fabricated. The top electrodes (TEs), such as Ag or Cu, affect the electrical characteristics of the Y2O3 RRAM devices. The oxidation process, mobile ion migration speed, and reduction process all impact the conductive filament formation of the indium–tin–oxide (ITO)/Y2O3/Ag and ITO/Y2O3/Cu RRAM devices. Between Ag and Cu, Cu can easily be oxidized due to its standard redox potential values. However, the conductive filament is easily formed using Ag TEs. After triggering the oxidation process, the formed Ag mobile metal ions can migrate faster inside Y2O3 active channel materials when compared to the formed Cu mobile metal ions. The fast migration inside the Y2O3 active channel materials successfully reduces the SET voltage and improves the number of programming–erasing cycles, i.e., endurance, which is one of the nonvolatile memory parameters. These results elucidate the importance of the electrochemical properties of TEs, providing a deeper understanding of how these factors influence the resistive switching characteristics of metal oxide-based atomic switches and conductive-metal-bridge-filament-based cells.

The effect of the top Ag electrode on local piezoelectric and the ferroelectric response of PVDF thin films in PVDF/Au/Si and Ag/PVDF/Au/Si multilayers is probed using dual AC resonance tracking piezo force microscopy (DART-PFM). The 4 wt% PVDF thin films are prepared on Au/Si using a spin coater and the top electrode Ag is deposited with the DC magnetron sputtering method. The structural and microstructural characteristics are analyzed using a Raman spectrometer, grazing incidence X-ray diffraction, scanning electron microscopy with electron dispersive spectroscopy, and atomic force microscopy. The local piezoelectric and ferroelectric characteristics are found to be dependent upon the presence or absence of the top Ag electrode. Both the device structures display typical bi-stable ferroelectric and piezoelectric switching. The resultant non-uniform electric field due to the absence of a top electrode shows ferroelectric switching at an applied voltages ≥ ± 20 V compared to the low-voltage (down to ± 5 V) switching on Ag/PVDF/Au junctions. Furthermore, a higher d33 coefficient recorded in Ag/PVDF/Au is discussed with uniform electric field distribution in the devices. Our study reveals a clear dependency of local piezoelectric and ferroelectric characteristics upon the top electrode and its local domain switching phenomena. [ABSTRACT FROM AUTHOR]

The top electrodes of organic solar cells (OSCs) are usually deposited by thermal evaporation in vacuum, which has become the major obstacle toward fully‐printed OSCs. The vacuum‐free printed top electrodes are highly desirable for the continuous production of OSCs. Here, the printing of low‐melting‐point alloy (LMPA) as cathodes in OSCs based on the D18:Y6 system is investigated. The Field's metal (FM) is focused with a melting point of 62 °C, which could be printed under moderate temperatures that are harmless to the active layers and solidifies at room temperature. More importantly, FM will not melt by solar radiation under practical scenarios. Direct ink writing is used to print the FM cathodes. Two printing modes are identified: the dragging mode in the far field to obtain rod electrodes, and the shearing mode in the near field to achieve relatively flat lamellas. The correlations between processing parameters and properties of the printed electrodes are elucidated. OSCs with printed FM cathodes exhibit the highest power conversion efficiency of 16.44%. The results demonstrate that this facile and robust direct LMPA writing technique is promising for high‐performance fully‐printed OSCs. [ABSTRACT FROM AUTHOR]

Monolithic perovskite/Silicon tandem solar cells have reached a certified efficiency of 29. 1% in recent years. In this review, we discuss material design for monolithic perovskite/Si tandem solar cells, with the focus on the top-cell development to improve their performance. Firstly, we introduce different types of transparent electrodes with high transmittance and low sheet-resistance used in tandem solar cells. We then discuss the development of the wide-bandgap perovskite absorber for top-cells, especially the strategies to obtain the perovskite layers with good efficiency and stability. In addition, as a special functional layer in tandem solar cells, the recombination layers play an important role in device performance, wherein different configurations are summarized. Furthermore, tandem device cost analysis is discussed. This review summarizes the progress of monolithic perovskite/Silicon tandem solar cells in a pragmatic perspective, which may promote the commercialization of this technology.

A semitransparent perovskite solar cell (PSC) with a dielectric/metal/dielectric (DMD) multilayer film as the top transparent electrode is investigated. Through adjusting the thickness and the deposition rate of Ag and WO3 layers, a transparent electrode with a low sheet resistance of 7 Ω sq−1 and high average visible transmittance (AVT) of 73% in the visible wavelength range of 400–800 nm is obtained. Using the resultant DMD film as the top transparent electrode and different bandgap perovskites of CH3NH3PbI3 (MAPbI3), CH(NH2)2PbI3 (FAPbI3), and FA0.5MA0.38Cs0.12PbI2.04Br0.96 as the optical active layer, a solar cell with a device architecture of ITO/SnO2/perovskite/spiro‐OMeTAD/MoO3/Ag/WO3 is fabricated. A series of efficient semitransparent PSCs with high transmittance are achieved. [ABSTRACT FROM AUTHOR]

Two top electrode (TE) metals, Pt and Ti, are deposited on VO X /Pt to investigate the effect of oxygen affinity TE on resistive switching (RS). The oxygen affinity electrode Ti significantly improves the variability and durability of the devices compared to the inert TE Pt. The TiO Y interfacial layer (IL) plays a vital role in RS as an oxygen reservoir between the Ti TE and the dielectric layer. During repeated RS, a rapid endurance degradation is observed for Pt/VO X /Pt. However, the resistance value in the high-resistance state (HRS) gradually decreases over the RS cycles for Ti/VO X /Pt. The oxygen ions in VO X are consumed and stored in TE Ti owing to the high oxygen affinity of Ti. This process causes an improvement in the uniformity and endurance for Ti/VO X /Pt. • Oxygen affinity electrode Ti improves the variability of RRAM devices. • TiO Y interfacial layer was used to suppress the loss of oxygen. • Stable DC endurance of Ti top electrode sample over 104 cycles. [ABSTRACT FROM AUTHOR]

The presence of voltage controlled negative differential resistance was observed in conduction characteristics recorded at room temperature for 300 nm thick spin‐coated films of graphene oxide (GO) sandwiched between indium tin oxide (ITO) substrates and top electrodes of sputtered gold (Au) film. The GO crystallites were found from the X‐ray diffraction studies to have an average size in the order of 7.24 nm and to be preferentially oriented along (001) plane. Raman spectroscopy suggested that the material consisted of multilayer stacks with the defects being located at the edges with an average distance of 1.04 nm apart. UV visible spectroscopy studies suggested that the band gap of the material was 4.3 eV, corresponding to direct transitions. The two‐terminal ITO/GO/Au devices exhibited memristor characteristics with scan‐rate dependent hysteresis, threshold voltage and On/Off ratios. A value of >104 was obtained for On/Off ratio at a scan rate of 400 mVs−1 and 4.2 V. [ABSTRACT FROM AUTHOR]

Monolithic perovskite/Silicon tandem solar cells have reached a certified efficiency of 29. 1% in recent years. In this review, we discuss material design for monolithic perovskite/Si tandem solar cells, with the focus on the top-cell development to improve their performance. Firstly, we introduce different types of transparent electrodes with high transmittance and low sheet-resistance used in tandem solar cells. We then discuss the development of the wide-bandgap perovskite absorber for top-cells, especially the strategies to obtain the perovskite layers with good efficiency and stability. In addition, as a special functional layer in tandem solar cells, the recombination layers play an important role in device performance, wherein different configurations are summarized. Furthermore, tandem device cost analysis is discussed. This review summarizes the progress of monolithic perovskite/Silicon tandem solar cells in a pragmatic perspective, which may promote the commercialization of this technology., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2020 Liu, Wang, Xu, Wu, Song and Chen.)

The fabrication of gallium oxide nanodots for the application of resistive random access memory (RRAM) using a process of atomic force microscopy (AFM) local anodic oxidation on an indium tin oxide conductive glass substrate is reported. In the atmospheric environment, an AFM probe tip contacts the gallium film locally. This gallium oxide nanodot acts as the insulator layer in a single unit of the RRAM. The structure describes the insulator layer (GaOx) sandwiched by the top (AFM tip) and bottom (Ga film) electrodes. Using current and voltage biased methods, the device switches from a high‐resistance state (HRS) to a low‐resistance state (LRS) and reset from LRS to HRS. Low read‐voltage is used to distinguish the high/low resistance to present the digital data. Presented results show the ability of atomic force microscopy anodic oxidation to produce 300 nm diameter gallium oxide nanodots on glass substrates for potentially high density RRAMs. [ABSTRACT FROM AUTHOR]