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The synthesis of uniform low-defect graphene on a catalytic metal substrate is getting closer to the industrial level. However, its practical application is still challenging due to the lack of an appropriate method for its scalable damage-free transfer to a device substrate. Here, an efficient approach for a defect-free, etchant-free, wrinkle-free, and large-area graphene transfer is demonstrated by exploiting a multifunctional viscoelastic polymer gel as a simultaneous shock-free adhesive and dopant layer. Initially, an amine-rich polymer solution in its liquid form allows for conformal coating on a graphene layer grown on a Cu substrate. The subsequent thermally cured soft gel enables the shock-free and wrinkle-free direct mechanical exfoliation of graphene from a substrate due to its strong charge-transfer interaction with graphene and excellent shock absorption. The adhesive gel with a high optical transparency works as an electron doping layer toward graphene, which exhibits significantly reduced sheet resistances without optical transmittance loss. Lastly, the transferred graphene layer shows high mechanical and chemical stabilities under the repeated bending test and exposure to various solvents. This gel-assisted mechanical transfer method can be a solution to connect the missing part between large-scale graphene synthesis and next-generation electronics and optoelectronic applications.

In order to ensure high-performance semitransparent perovskite solar cells (ST-PSCs), the deposition of high-quality scalable transparent cathodes on ST-PSCs at room temperature is necessary. In this study, we designed an amorphous InGaTiO (IGTO) electrode, prepared by linear facing target sputtering (LFTS) as a transparent cathode for ST-PSCs. Even in the room temperature sputtering process, the amorphous IGTO cathode showed a low sheet resistance of 9.895 Ohm/square and a high optical transmittance of 87.53% without the occurrence of in situ or postannealing, unlike Sn-doped In2O3 (ITO) electrodes. Due to its complete amorphous structure and low energy sputtering, the amorphous IGTO electrode showed superior mechanical properties, when compared to other typical crystalline ITO films. Additionally, the LFTS process led to a low energy deposition of the amorphous IGTO cathode on ST-PSCs, and did not result in plasma damage on perovskite active layers, which is often typical in conventional situations of direct current sputtering. On the basis of these optimized plasma damage-free sputtering conditions, we examined the feasibility of LFTS-grown IGTO cathodes for ST-PSCs. In our results, we observed that a similar performance of the ST-PSC with an IGTO cathode with the opaque PSC with Ag cathode, indicated that amorphous IGTO cathode is a prospective transparent cathode for ST-PSCs on both rigid or flexible substrates.

We investigated the rapid thermal annealing (RTA) sequence effect on the electrical, optical, morphological, and structural properties of transparent thin film transistors (TTFTs) with an indium gallium zinc oxide (IGZO) channel and an indium tin oxide (ITO) source/drain. The electrical and optical properties of the IGZO channel and the ITO source/drain electrodes were compared as a function of RTA temperature in ambient air. The performance of a TTFT with only an RTA-processed IGZO channel was compared with that of a TTFT with an RTA-processed IGZO channel and ITO source/drain electrodes. Using the circular transmission line measurement (CTLM) method, we suggest a possible mechanism that explains the effect of the RTA process on the performance of the TTFT with only an annealed IGZO channel vs. that with an annealed IGZO/ITO multilayer. The TTFT with an RTA-processed IGZO/ITO multilayer showed a threshold voltage shift, an improved on/off ratio of 3.54 × 1011, a subthreshold swing of 0.33 V/decade, and a high mobility of 8.69 cm2/V·s. This indicates that simultaneous RTA processing for an IGZO channel and an ITO electrode is beneficial for the fabrication of high-performance TTFTs.

In this study, the electrical and the optical properties of the amorphous indium-zinc-tin oxide (IZTO) thin films that had been grown using a cosputtering system were investigated as a function of the oxygen flow rate during growth. The optical constants of the IZTO thin films were obtained by applying the Drude and the parametric optical constant models to the ellipsometric angles, Ψ and Δ. We estimated the optical gap energies of the IZTO thin films from their absorption coefficients (α). The Drude tail amplitudes in the optical spectra were found to decrease under the deposition condition of increasing oxygen flow. The resistivity of the IZTO films was measured to be as low as 0.547 mΩ·cm at an oxygen flow rate of 0.3 sccm. Further, the Hall carrier concentrations and the mobilities were measured. We determined the effective masses of the IZTO thin films by using a combination of their optical and electrical parameters. The effective mass of the amorphous IZTO thin films decreased from 0.61 to 0.44 m0 as the oxygen gas flow rate was increased. Assuming a linear dependence of the effective mass on the carrier concentration, we estimated the effective mass at the conduction band minimum. The optically and electrically measured resistivities and mobilities of the amorphous IZTO thin films were equal because the films were free of grain boundaries; therefore, no scattering of free carriers from such grain boundaries had to be considered.

We investigated the characteristics of thermally evaporated fullerene (C60)/Ag/C60 (CAC) multilayer films for use in semi-transparent perovskite solar cells (PSCs) and thin-film heaters (TFHs). The top and bottom C60 layers and Ag interlayer were prepared using multi-source thermal evaporation, and the thickness of the Ag interlayer was investigated in detail for its effects on the resistivity, optical transmittance, and mechanical properties of the CAC electrodes. We used a figure-of-merit analysis to obtain a CAC electrode with a smooth surface morphology that exhibited a sheet resistance of 5.63 Ohm/square and an optical transmittance of 66.13% at a 550 nm wavelength. We conducted mechanical deformation tests to confirm that the thermally evaporated multilayer CAC electrode has a high durability, even after 10,000 times of inner and outer bending, rolling, and twisting due to the flexibility of the amorphous C60 and Ag interlayer. We evaluated the feasibility of using CAC electrodes for semi-transparent PSCs and TFHs. The semi-transparent PSC with 1.08 cm2 active area prepared with a transparent multilayer CAC cathode showed a power conversion efficiency (PCE) of 5.1%. Furthermore, flexible TFHs (2.5 × 2.5 cm2) fabricated on a thermally evaporated CAC electrode show a high saturation temperature of 116.6 C, even at a low input voltage of 4.5 V, due to a very low sheet resistance. Based on the performance of the PSCs and TFHs, we conclude that the thermally evaporated multilayer CAC electrode is promising for use as a transparent conductive electrode (TCE) for semi-transparent PSCs and TFHs, with characteristics comparable to sputtered TCEs., GRAPHICAL ABSTRACT

We fabricated highly effective and transparent film heaters based on a conductive Ag layer sandwiched in between InZnSiO films. This multilayer heater was deposited on a PET film at room temperature using pilot-scale roll-to-roll (RTR) sputtering machine. Due to the selected substrate, the heater was flexible and passed the 10 mm bending radius test. The InZnSiO/Ag/InZnSiO (IAI) multilayer heater displayed a high optical transmittance of 91.91% and a relatively low sheet resistance of 7.83 Ω/sq. This is an excellent chemical combination for fabricating a low voltage and transparent film heater. The time-temperature profiles and heat distribution analysis revealed that the best performance of the transparent film heater was at 2.4 V applied bias case. Due to high mechanical durability, high transparency and required low operating voltage the RTR sputtered IAI multilayer which can be considered one of the best candidates for fabricating highly flexible and transparent film heaters.

We report on a simple and efficient process to enhance the performance of perovskite solar cells by using ITO electrodes with a nanoporous surface formed by wet-etching of self-agglomerated Ag nanoparticles. Effective removal of the Ag nanoparticles embedded in the surface of the ITO electrodes result in a nanoporous structure without changing the ITO's sheet resistance (10.17 Ω/square) and optical transmittance (89.08%) at a 550 nm wavelength. Examinations with a scanning electron microscope, a transmission electron microscope, and two-dimensional porous mapping show that the nanoporous ITO surface has an increased contact area with the electron transport layer, which enhanced the carrier extraction efficiency of the perovskite solar cells. Compare to perovskite solar cells fabricated on typical ITO with a flat surface morphology, the perovskite solar cells fabricated on the nanoporous-surface ITO show a higher fill factor of 81.1% and a power conversion efficiency of 20.1%. These results indicate that modified ITO surfaces with nano-scale porosity provide a simple and efficient method to improve the power conversion efficiency of perovskite solar cells without a complicated process.

As a cost-effective, indium-free, flexible, and highly transparent electrode for flexible thin-film heaters and heat-shielding films, ZnSnO(ZTO)/AgPdCu(APC)/ZTO multi-stacked films were fabricated by using 1500-mm–width, roll-to-roll (RTR) sputtering at room temperature. The optimized RTR-sputtered ZTO/APC/ZTO film showed a very low sheet resistance (3.43 ohm/square), high optical transmittance (80.99%), and small inner/outer critical bending radii (1 and 2 mm, respectively), even when it was processed at room temperature. In particular, the better flexibility of the ZTO/APC/ZTO films, relative to typical ITO films, was confirmed by lab-scale bending, rolling, twisting, and folding tests. Due to the very low sheet resistance, superior flexibility, and low transmittance in the near-infrared wavelength region, flexible and transparent thin-film heaters (TFHs) and flexible heat-shielding films (HSFs) made with the ZTO/APC/ZTO films showed better performance than typical ITO-based TFHs and HSFs. This suggests that the RTR–sputtered, indium-free ZTO/APC/ZTO films can be applied as transparent and flexible electrode materials in cost-effective and multi-functional smart windows for buildings and automobiles.

We report the characteristics of Sn-doped In2O3 (ITO) films intended for use as transparent conducting electrodes; the films were prepared via a five-generation, in-line type, cylindrical, rotating magnetron sputtering (CRMS) system as a function of film thickness. By using a rotating cylindrical ITO target with high usage (∼80%), we prepared high conductivity, transparent ITO films on five-generation size glass. The effects of film thickness on the electrical, optical, morphological, and structural properties of CRMS-grown ITO films are investigated in detail to correlate the thickness and performance of ITO films. The preferred orientation changed from the (2 2 2) to the (4 0 0) plane with increasing thickness of ITO is attributed to the stability of the (4 0 0) plane against resputtering during the CRMS process. Based on X-ray diffraction, surface field emission scanning electron microscopy, and cross-sectional transmission electron microscopy, we suggest a possible mechanism to explain the preferred orientation and effects of film thickness on the performance of CRMS-grown ITO films.

We report high performance flexible Sn-doped In2O3 (ITO) films prepared by in-line type vertical plasma arc ion plating for high performance flexible perovskite solar cells. Even at room temperature deposition, the ion-plated ITO film showed a low sheet resistance of 15.75 Ohm per square, a high average optical transmittance of 85.88% and a small outer bending radius of 5 mm because energetic ITO ions accelerated to the substrate led to better crystallinity and adhesion than sputtered ITO films. In addition, the ion-plated ITO films showed atomically flat and smooth surfaces due to different growth mechanisms and the absence of resputtering effects during the ion plating process. Flexible perovskite solar cells fabricated on the ion-plated ITO electrodes showed a higher power conversion efficiency of 16.8% than the sputtered ITO-based perovskite solar cell, indicating the potential of ion plated ITO films as promising flexible and transparent electrodes for perovskite solar cells.

We developed radio frequency (RF) magnetron sputtered amorphous vanadium pentoxide (V2O5) film to use in place of typical PEDOT:PSS or solution-processed metal oxide hole injection layer (HIL) in quantum dot light-emitting diodes (QLEDs). The electrical, optical, and chemical properties of the sputtered V2O5 HIL were correlated with the oxygen flow rate at room temperature. At optimized sputtering conditions, the V2O5 film showed a high optical transparency of 91.93% in the visible wavelength region and a work function of 4.73 eV, which is suitable for HIL in QLEDs. We also investigated the performance of QLEDs with sputtered V2O5 HIL as a function of oxygen flow rate. The QLEDs with optimized V2O5 HIL exhibited a maximum luminance of 198,542 cd/m2, a turn-on voltage of 1.7 V, a max external quantum efficiency of about 8.3%, and a current efficiency of 20.3 cd/A, thereby making it comparable to typical PEDOT:PSS HIL-based QLEDs. The successful operation of QLEDs with sputtered V2O5 as HIL demonstrated that it could be used instead of other materials for next-generation large-area QLED displays.

In this study, we report on high performance semi-transparent perovskite solar cells (PSCs) with bidirectional transparent electrodes for use in building-integrated photovoltaics (BIPV). Using a typical magnetron sputtered InSnO (ITO) anode and a low energy sputtered InZnSnO (IZTO) cathode, we fabricated bidirectional transparent electrodes for semi-transparent PSCs. In particular, by the sequential sputtering of a thin buffer and then a thick dense IZTO layer (two-step sputtering), we fabricated a transparent IZTO cathode for a p-i-n planar type PSC without any plasma damage. Compared to the power conversion efficiency (PCE 3.43%) of PSCs with an ITO cathode prepared by typical DC magnetron sputtering, the PSC with a two-step sputtered IZTO cathode showed a much higher PCE (15.72%) due to the absence of plasma damage. The high PCE of the semi-transparent PSC with IZTO cathode is comparable to the PCE (17.04%) of an opaque PSC with opaque Ag cathode. Furthermore, with diluted perovskite solution, we able to achieve PCE of 13.61% and AVT of 24.70% both high enough to use as PSC for BIPV. These results demonstrate that the two-step linear facing target sputtering (FTS) process is a feasible approach to make high-quality transparent top cathodes for semi-transparent PSCs. Considering the mass-production of semi-transparent PSCs for BIPV, FTS-based two-step sputtering has great potential to become a key technique for producing smart windows that will replace typical solution coating or other complicated transfer processes.

Ga-doped ZnO (GZO)-graded layer, facilitating electron extraction from electron transport layer, was integrated on the surface of transparent indium tin oxide (ITO) cathode by using graded sputtering technique to improve the performance of planar n-i-p perovskite solar cells (PSCs). The thickness of graded GZO layer was controlled to optimize GZO–indium tin oxide (ITO) combined electrode for planar n-i-p PSCs. At optimized graded thickness of 15 nm, the GZO–ITO combined electrode showed an optical transmittance of 95%, a resistivity of 2.3 × 10−4 Ohm cm, a sheet resistance of 15.6 Ohm/square, and work function of 4.23 eV, which is well matched with the 4.0-eV lowest unoccupied molecular orbital of [6,6]-phenyl-C61-butyric acid methyl ester. Owing to enhanced extraction of electron by the graded GZO, the n-i-p PSC with GZO–ITO combined electrode showed higher power conversion efficiency (PCE) of 9.67% than the PCE (5.25%) of PSC with only ITO electrode without GZO-graded layer. In addition, the GZO integrated-ITO electrode acts as transparent electrode and electron extraction layer simultaneously due to graded mixing of the GZO at the surface region of ITO electrode., Graphical abstract

(ta-C) films coated through the filtered cathodic vacuum arc (FCVA) process as a hole transport layer (HTL) for perovskite solar cells (PSCs) and quantum dot light-emitting diodes (QDLEDs). The p-type ta-C film has several remarkable features, including ease of fabrication without the need for thermal annealing, reasonable electrical conductivity, optical transmittance, and a high work function. X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy examinations show that the electrical properties (sp3/sp2 hybridized bond) and work function of the ta-C HTL are appropriate for PSCs and QDLEDs. In addition, in order to correlate the performance of the devices, the optical, surface morphological, and structural properties of the FCVA-grown ta-C films with different thicknesses (5 ~ 20 nm) deposited on the ITO anode are investigated in detail. The optimized ta-C film with a thickness of 5 nm deposited on the ITO anode had a sheet resistance of 10.33 Ω−2, a resistivity of 1.34 × 10−4 Ω cm, and an optical transmittance of 88.97%. Compared to the reference PSC with p-NiO HTL, the PSC with 5 nm thick ta-C HTL yielded a higher power conversion efficiency (PCE, 10.53%) due to its improved fill factor. Further, the performance of QDLEDs with 5 nm thick ta-C hole injection layers (HIL) showed better than the performance of QDLEDs with different ta-C thicknesses. It is concluded that ta-C films have the potential to serve as HTL and HIL in next-generation PSCs and QDLEDs., Graphical abstract

Materials with anisotropic properties have different electronic structures and photoelectrochemical (PEC) performance depending on the facet. Herein, we controlled the morphology of WO3 nanoflakes, and the ratio of the revealed WO3 facet using patterned F-doped SnO2 fabrication by means of direct printing. In the case of WO3 NF synthesized on patterned FTO (FB-WO3/BiVO4), the proportion of the (002) facet decreased and that of the (200) and (020) facets increased in comparison to the case when NF were synthesized on flat FTO (B-WO3/BiVO4). As the facet ratio changed, the band structure and efficiency changed. The photocurrent density of FB-WO3/BiVO4 was 1.50 mA/cm2, which was 34% higher than that of B-WO3/BiVO4 (1.12 mA/cm2) at 1.23 VRHE. Our results indicate that the efficiency of PEC water splitting can be increased by engineering the exposed facet according to the shape of the substrate, rather than varying the synthetic method.

We have studied characteristics of tin-doped indium oxide (ITO) films sputtered on flexible invar metal foil covered with an insulating SiO2 layer at room temperature to use as transparent electrodes coated substrates for curved perovskite solar cells. Sheet resistance, optical transmittance, surface morphology, and microstructure of the ITO films on SiO2/invar substrate are investigated as a function of the thickness from 50 to 200 nm. The optimized ITO film exhibits a low sheet resistance of 50.21 Ohm/square and high optical transmittance of up to 94.31% even though it is prepared at room temperature. In particular, high reflectance of invar metal substrate could enhance the power conversion efficiency of curved perovskite solar cell fabricated on the ITO/SiO2/invar substrate. In addition, critical bending radius of the 150 nm-thick ITO film is determined by lab-designed outer and inner bending tests to show feasibility as flexible electrode. Furthermore, dynamic fatigue test is carried out to show flexibility of the ITO film on invar metal substrate. This suggests that the ITO/SiO2/invar substrate can be applied as flexible electrodes and substrates for curved perovskite solar cells.