Showing papers in "Japanese Journal of Applied Physics in 2012"

Diamond Field-Effect Transistors with 1.3 A/mm Drain Current Density by Al$_{2}$O$_{3}$ Passivation Layer

Abstract: Using nitrogen-dioxide (NO2) adsorption treatment and Al2O3 passivation technique, we improved drain current (IDS) of hydrogen-terminated (H-terminated) diamond field-effect transistors (FETs). The Al2O3 passivation layer also serves as a gate-insulator in a gate region. Maximum IDS (IDSmax) of -1.35 A/mm was obtained for the diamond FETs with NO2 adsorption and the Al2O3 passivation layer. This IDSmax is the highest ever reported for diamond FETs and indicates that the Al2O3 passivation layer can stabilize adsorbed NO2, which increases the hole carrier concentration on the H-terminated diamond surface. In RF small-signal characteristics, the diamond FETs with NO2 adsorption and the Al2O3 passivation layer showed high cutoff-frequency (fT) and maximum frequency of oscillation (fmax) in a wide gate–source voltage (VGS) range (>10 V). This is because the Al2O3 gate insulator with a high potential barrier against hole carriers can confine and control the high concentration of hole carriers and then high forward-bias voltage can be applied without noticeable gate leakage current.

18-GHz, 4.0-aJ/bit Operation of Ultra-Low-Energy Rapid Single-Flux-Quantum Shift Registers

Abstract: We demonstrate rapid single-flux-quantum (RSFQ) circuits with reduced energy consumption by lowering the driving voltages and critical currents of Josephson junctions (JJs). At lowered voltages, the energy statically consumed by bias resistors (which is dominant in RSFQ circuits) is reduced. In addition, we show that when RSFQ circuits are driven by lowered constant voltages, the dynamic energy consumption resulting from the switching of JJs is reduced because of the suppression of the amplitudes of the signal voltage pulses, even though the switching speed becomes slower. Utilization of miniaturized JJs with smaller critical currents also leads to the reduction of static and dynamic energy consumption without decreasing the switching speed. We have designed and tested ultra-low-energy 8-bit shift registers, and verified the correctness of high-speed operations up to 18 GHz. The average energy consumption, including that at the bias resistors, was measured at 4.0 aJ/bit, which represents an energy efficiency two orders of magnitude better than that of standard RSFQ circuits.

Successful Growth of Conductive Highly Crystalline Sn-Doped ?-Ga2O3 Thin Films by Fine-Channel Mist Chemical Vapor Deposition

Abstract: Highly crystalline α-phase gallium oxide (Ga2O3) thin films were grown by fine-channel mist chemical vapor deposition on c-sapphire substrates at 400 °C at a deposition rate of more than 20 nm/min. The thin films were doped with Sn(IV) atoms, which were obtained from Sn(II) chloride by the reaction SnCl2+ H2O2+ 2HCl→SnCl4+ 2H2O. Conductive α-phase Ga2O3 thin films were successfully grown from source solutions containing less than 10 at. % Sn(IV). The source solution containing 4 at. % Sn(IV) resulted in obtaining a thin film with an n-type conductivity as high as 0.28 S cm-1, a mobility of 0.23 cm2 V-1 s-1, a carrier concentration of 7×1018 cm-3, and a full width at half maximum (FWHM) of the (0006) reflection X-ray rocking curve as low as 64 arcsec.

Growth and Band Gap Control of Corundum-Structured $\alpha$-(AlGa)$_{2}$O$_{3}$ Thin Films on Sapphire by Spray-Assisted Mist Chemical Vapor Deposition

Abstract: Following the previous achievement of highly crystalline α-Ga2O3 thin films on c-plane sapphire, the growth of corundum-structured α-(AlxGa1-x)2O3 was examined aiming at the future application of α-(AlxGa1-x)2O3/Ga2O3 heterostructures to power devices and other functional devices. The results show the control of x and band gap up to 0.81 and 7.8 eV, respectively, maintaining the dominant corundum structure. The transmission electron microscope observation suggested the formation of the crystallographically good interface of α-(AlxGa1-x)2O3/Ga2O3 without the severe generation of threading dislocation lines from the interface.

Electrical Conductive Corundum-Structured $\alpha$-Ga$_{2}$O$_{3}$ Thin Films on Sapphire with Tin-Doping Grown by Spray-Assisted Mist Chemical Vapor Deposition

Abstract: We report the fabrication of electrical conductive tin-doped α-Ga2O3 thin films on c-plane sapphire substrates The mist chemical vapor deposition method brought tin-doped α-Ga2O3 thin films with high crystallinity without noticeable other phases, as highlighted by the full-width of X-ray diffraction ω-scan rocking curves as small as 40 arcsec, for the tin atomic density in the film upto ~1020 cm-3 The resistivity decreased by more doping of tin, and the α-Ga2O3 thin film with minimum resistivity exhibited n-type conductivity with the Hall mobility of 28 cm2 V-1 s-1 and the carrier density of 27 ×1019 cm-3

Overview of Materials and Power Applications of Coated Conductors Project

Abstract: There are high expectations for coated conductors in electric power applications such as superconducting magnetic energy storage (SMES) systems, power cables, and transformers owing to their ability to contribute to stabilizing and increasing the capacity of the electric power supply grid as well as to reducing CO2 emission as a result of their high critical-current characteristics. Research and development has been performed on wires/tapes and electric power devices worldwide. The Materials and Power Applications of Coated Conductors (M-PACC) Project is a five-year national project in Japan started in 2008, supported by the Ministry of Economy, Trade and Industry (METI) and the New Energy and Industrial Technology Development Organization (NEDO), to develop both coated conductors that meet market requirements and basic technologies for the above-mentioned power applications using coated conductors. In this article, research and development results are reviewed and compared with the interim/final targets of the project, and future prospects are discussed.

Evaluation of Misfit Relaxation in $\alpha$-Ga$_{2}$O$_{3}$ Epitaxial Growth on $\alpha$-Al$_{2}$O$_{3}$ Substrate

Abstract: Corundum-structured α-Ga2O3 epitaxial thin films were grown on c-plane α-Al2O3 (sapphire) substrates by a mist chemical vapor deposition method. To reveal the defect structures, the α-Ga2O3 film was observed by high-resolution transmission electron microscopy (TEM). We found that the α-Ga2O3 thin film was in-plane compressive stressed from the α-Al2O3 substrate. Although misfit dislocations were periodically generated at the α-Ga2O3/α-Al2O3 interface owing to the large lattice mismatches between α-Ga2O3 and α-Al2O3, 3.54% (c-axis) and 4.81% (a-axis), most of the misfit dislocations did not thread through the layer. An extra-half plane was {110} consisting only of Ga. Screw dislocations were not confirmed, i.e., the density was under 107 cm-2. The threading dislocation density was 7 ×1010 cm-2.

Evaluation of Off-State Current Characteristics of Transistor Using Oxide Semiconductor Material, Indium--Gallium--Zinc Oxide

Abstract: We measured a significantly low off-state current (135 yA/µm at 85 °C) of a metal oxide semiconductor (MOS) transistor using indium–gallium–zinc oxide (IGZO), which is an oxide semiconductor material. Note that "y" is 10-24. A transistor in which the hydrogen concentration in an IGZO film is lowered (5×1019 cm-3 or lower) was used. To estimate the minute current accurately, we established a measurement method in which changes in the amount of electrical charge are measured for a long time. Such extremely low off-state current characteristics show promise for new applications of IGZO transistors in memories.

High Temperature Superconductor Terahertz Emitters: Fundamental Physics and Its Applications

Abstract: Coherent and continuous radiation sources of the electromagnetic (EM) waves at terahertz (1 THz = 1012 c/s) frequencies using a mesa structure fabricated from high temperature superconducting Bi2Sr2CaCu2O8+δ single crystals are described with a special emphasis on the physics of the radiation mechanism and the applications. After the intensive studies of many mesas fabricated with different conditions, it is revealed that the ac-Josephson effect works as a primary driving mechanism of the radiation and the cavity resonance needed for stronger radiation plays an additional role to the mechanism, although both are working together while radiating. A prototype of the imaging machine for multipurpose uses has successfully been developed.

Comprehensive Investigation of Single Crystal Diamond Deep-Ultraviolet Detectors

Abstract: The wide bandgap of diamond, along with its extreme semiconductor properties, offers the promising route for deep-ultraviolet (DUV) detection, especially under solar-blind condition and harsh environments The ideal photodetector should generally satisfy the 5S requirements such as high sensitivity, high signal-to-noise ratio, high spectral selectivity, high speed, and high stability In this paper, we comprehensively investigate the DUV detectors fabricated from various kinds of single crystal diamonds such as boron-doped diamond homoepitaxial layer, intrinsic diamond homoepitaxial layers with different thicknesses, and single crystal diamond substrates The post process such as hydrogen plasma treatment on the performance of the DUV detectors is also examined The strategies to develop high-performance diamond DUV detectors are provided

Frontiers of Research on Iron-Based Superconductors toward Their Application

Abstract: The recent discovery of iron-based superconductors has evoked enthusiasm for extensive research on these materials because they form the second high-temperature superconductor family after the copper oxide superconductors and impart an expectation for materials with a higher transition temperature (Tc). It has also been clarified that they have peculiar physical properties including an unconventional pairing mechanism and superconducting properties preferable for application such as a high upper critical field and small anisotropy. This paper reviews the research on thin films, Josephson junctions, and superconducting wires and tapes made from iron-based superconductors, which has been performed toward the realization of future applications. Though there are many technical hurdles toward the practical application of these materials, some promising features such as a high critical current density in thin films under high magnetic fields and advantageous grain boundary properties over copper oxides have been clarified.

High-Current Metal Oxide Semiconductor Field-Effect Transistors on H-Terminated Diamond Surfaces and Their High-Frequency Operation

Abstract: Metal semiconductor field-effect transistors (MESFETs) or metal oxide semiconductor FETs (MOSFETs) can be fabricated on hydrogen-terminated diamond without losing the surface hydrogen–carbon bonds and the surface adsorbates responsible for the surface carrier generation. Those FETs show their best performance in diamond transistors. The maximum drain current density is above 1 A/mm and the highest transconductance is 400 mS/mm. These values are comparable to those of modern FETs made of Si or III–V semiconductors. Regarding RF performance, the highest cutoff frequency reaches nearly 50 GHz. The power handling capability exceeds those of Si and GaAs at 1 GHz. The function of surface adsorbates and their stabilization are crucial for the application of diamond FETs.

Design Guideline of Si-Based L-Shaped Tunneling Field-Effect Transistors

Abstract: In this work, novel L-shaped tunneling field-effect transistors (TFETs) have been proposed. The proposed L-shaped TFETs feature higher on-current (Ion) and lower subthreshold swing (SS) than conventional TFETs. It is because L-shaped TFETs have large cross-sectional area of band-to-band tunneling junction which is perpendicular to the channel direction and their tunneling barrier width (Wt) is defined by the length of an intrinsic silicon region. As the devices are based on the Si without any other material, it can be fabricated with well-established Si process technology. In addition, it can moderate some issues come from scaling down and enlarging tunneling area due to its mesa structure. Simulation results have confirmed the superiority of L-shaped TFETs over conventional TFETs. Additionally, the effect of some device parameters on device performance has been investigated for the clear verification of its operation mechanism and the optimization.

Preparation of Cu$_{2}$SnS$_{3}$ Thin Films by Sulfurization of Cu/Sn Stacked Precursors

Abstract: Cu2SnS3 (CTS) has been reported to have various band gap energies in the range of 0.93–1.77 eV and an absorption coefficient of 1.0×104 cm-1. It consists of elements that are inexpensive due to their abundance in Earth's crust. Consequently, CTS is expected to be utilized in the absorber layers of thin-film solar cells. In this study, Cu/Sn stacked-layer thin-film precursors were deposited on glass and glass/Mo substrates by electron beam evaporation. CTS thin films were fabricated by sulfurizing the precursors at temperatures of 450–580 °C for 2 h in an atmosphere of N2 and sulfur vapor. CTS films were estimated to have band gap energies of 0.96–1.00 eV by extrapolation. A solar cell fabricated using a CTS thin film sulfurized at 580 °C exhibited an open-circuit voltage of 211 mV, a short-circuit current of 28.0 mA/cm2, a fill factor of 0.43, and a conversion efficiency of 2.54%.

Large Defect-Free Synthetic Type IIa Diamond Crystals Synthesized via High Pressure and High Temperature

Abstract: Large high-quality type IIa diamond crystals measuring up to 12 mm in diameter were successfully synthesized by the temperature gradient method at high pressure and high temperature, using high-crystalline-quality (001)-oriented seed crystals, and by controlling the temperature conditions with high precision. The X-ray projection topograph using a synchrotron radiation beam revealed that the large synthetic diamond crystals are characterized by high-crystalline-quality, having no dislocation or stacking fault in the (001) growth sectors in the upper part of the crystals grown on seeds. Diamond crystals containing a large defect free area of 5 ×5 mm2 or more were successfully produced by controlling the temperature strictly on the low-temperature side in the synthesis region for growing type IIa diamond crystals to allow the (001) growth sectors to become dominant.

Experimental Test of Landauer's Principle at the Sub-k_{\text{B}} T Level

Abstract: Landauer's principle connects the logical reversibility of computational operations to physical reversibility and hence to energy dissipation, with important theoretical and practical consequences. We report the first experimental test of Landauer's principle. For logically reversible operations we measure energy dissipations much less than kBTlog 2, while irreversible operations dissipate much more than kBTlog 2. Measurements of a logically reversible operation on a bit with energy 30 kBT yield an energy dissipation of 0.01 kBT.

Cu$_{2}$SnS$_{3}$ Thin-Film Solar Cells from Electroplated Precursors

Abstract: Cu2SnS3 (CTS) contains non-rare metals and it has suitable optical characteristics for the absorber layer of thin-film solar cells. In this study, CTS thin films were fabricated by sulfurizing Cu?Sn precursors deposited by co-electrodeposition. Solar cells with a structure glass/Mo/CTS/CdS/ZnO:Al/Al were fabricated from the films. The best cell had an efficiency of 2.84%. A relatively high conversion efficiency was obtained from films with Cu/Sn?2.

Hotspot Location Shift in the High-Power Phosphor-Converted White Light-Emitting Diode Packages

Abstract: Thermal management of high-power light-emitting diodes (LEDs) plays an important role in determining their optical properties, reliability, and lifetime. In this paper, we present a method to study the temperature field of phosphor-converted LED packages by combining the Monte Carlo optical simulation and finite element simulation together. The temperature field, including the heat generation in both LED chip and phosphor layer, are presented and analyzed. It was found that temperature increased with the increase in phosphor concentration and the hotspot location in remote phosphor-coating packages shifted with the changes in phosphor concentration, while there was no shift in direct phosphor-coating packages. It was concluded that the hotspot location in the high-power phosphor-converted white LED packages depended on phosphor concentrations as well as packaging methods.

Direct Current and Microwave Characteristics of Sub-micron AlGaN/GaN High-Electron-Mobility Transistors on 8-Inch Si(111) Substrate

Abstract: We report for the first time the DC and microwave characteristics of sub-micron gate (~0.3 µm) AlGaN/GaN high-electron-mobility transistors (HEMTs) on 8-in. diameter Si(111) substrate. The fabricated sub-micron gate devices on crack-free AlGaN/GaN HEMT structures exhibited good pin.-off characteristics with a maximum drain current density of 853 mA/mm and a maximum extrinsic transconductance of 180 mS/mm. The device exhibited unit current-gain cut-off frequency of 28 GHz, maximum oscillation frequency of 64 GHz and OFF-state breakdown voltage of 60 V. This work demonstrates the feasibility of achieving good performance AlGaN/GaN HEMTs on 8-in. diameter Si(111) for low-cost high-frequency and high-power switching applications.

High-Performance Thin Film Transistor with Amorphous In2O3–SnO2–ZnO Channel Layer

Abstract: We have developed a high-mobility and high-processability oxide semiconductor using amorphous In2O3–SnO2–ZnO (a-ITZO) as the channel material. An a-ITZO thin-film transistor (TFT) was fabricated by a back-channel-etch process. Its field effect mobility was more than 20 cm2 V-1 s-1 and its subthreshold swing was 0.4 V s-1, which makes it a promising candidate for next-generation TFTs.

Effects of Metal Electrode on the Electrical Performance of Amorphous In-Ga-Zn-O Thin Film Transistor

Abstract: Effects of metal electrode on the electrical performance of amorphous In–Ga–Zn–O (a-IGZO) thin film transistor (TFT) have been studied. Electrical performances and interface stability between Mo, Al, and Cu electrode and a-IGZO semiconductor have been investigated before and after air-annealing. No inter-diffusion and interfacial reaction has been observed between Mo and a-IGZO and the turn-on voltage of the Mo electrode TFT was 0 V after annealing. As for Al, Al oxide was formed at the interface, and the number of conduction electrons in a-IGZO increased. Thus, a negative turn-on voltage was observed after air-annealing. As for Cu, Cu diffused into a-IGZO during air-annealing and acted as an acceptor. Therefore the a-IGZO TFT with a Cu electrode had a positive turn-on voltage and sub-threshold slope increased after air-annealing. These results indicate that the transistor performance can be affected by the metal types due to inter-diffusion or interfacial reaction between metal and a-IGZO.

Film Sensor Device Fabricated by a Piezoelectric Poly(L-lactic acid) Film

Abstract: Synthetic piezoelectric polymer films produced from petroleum feedstock have long been used as thin-film sensors and actuators. However, the fossil fuel requirements for synthetic polymer production and carbon dioxide emission from its combustion have raised concern about the environmental impact of its continued use. Eco-friendly biomass polymers, such as poly(L-lactic acid) (PLLA), are made from plant-based (vegetable starch) plastics and, thus, have a much smaller carbon footprint. Additionally, PLLA does not exhibit pyroelectricity or unnecessary poling. This suggests the usefulness of PLLA films for the human–machine interface (HMI). As an example of a new HMI, we have produced a TV remote control using a PLLA film. The intuitive operation provided by this PLLA device suggests that it is useful for the elderly or handicapped.

Growth enhancement of radish sprouts induced by low pressure o 2 radio frequency discharge plasma irradiation

Abstract: We studied growth enhancement of radish sprouts (Raphanus sativus L.) induced by low pressure O2 radio frequency (RF) discharge plasma irradiation. The average length of radish sprouts cultivated for 7 days after O2 plasma irradiation is 30–60% greater than that without irradiation. O2 plasma irradiation does not affect seed germination. The experimental results reveal that oxygen related radicals strongly enhance growth, whereas ions and photons do not.

Internal Quantum Efficiency and Nonradiative Recombination Rate in InGaN-Based Near-Ultraviolet Light-Emitting Diodes

Abstract: The internal quantum efficiency (IQE) of three types of InGaN-based near-UV light-emitting diodes (LEDs) grown on different substrates was studied by excitation-power-density-dependent and temperature-dependent photoluminescence (PL) spectroscopy. IQE was evaluated under both the band-to-band excitation of GaN cladding layers and the selective excitation of InGaN active layers. A correlation between IQE and threading dislocation density was clearly observed under both excitation conditions. In addition, the dynamics of radiative and nonradiative recombinations was studied by time-resolved PL spectroscopy. The rate of nonradiative recombination was evaluated by measuring temperature-dependent nonradiative recombination lifetime. The validity of our method for estimating IQE is discussed on the basis of the correlation between IQE and nonradiative recombination rate for three LEDs with different threading dislocation densities.

Magnetic Anisotropy and Chemical Order of Artificially Synthesized L10-Ordered FeNi Films on Au–Cu–Ni Buffer Layers

Abstract: L10-FeNi films were grown by alternate monatomic layer deposition on Au–Cu–Ni buffer layers at several substrate temperatures (Ts), and the relation between the uniaxial magnetic anisotropy energy (Ku) and the long-range chemical order parameter (S) was investigated A large Ku of (70 ±02) ×106 erg/cm3 and S of 048 ±005 were obtained The value of Ku was larger than those reported previously for artificially synthesized FeNi films It was first found that both Ku and S increased with Ts, and Ku was roughly proportional to S

Deep levels in n-GaN Doped with Carbon Studied by Deep Level and Minority Carrier Transient Spectroscopies

Abstract: Electron and hole traps in the carbon doping of n-type GaN films grown by metal–organic chemical vapor deposition were investigated by deep level and minority carrier transient spectroscopies. Four electron traps were observed in the samples. Of these traps, the electron trap concentration of E2 (Ec-0.40 eV) rose with increasing C incorporation. Two hole traps H1 (Ev + 0.86 eV) and H2 also showed the dependence of C doping concentration. According to these results, traps E2, H1, and H2 correspond to C-related defects. Moreover, the energy level of H1 was consistent with an ionization energy of 0.9 eV of CN acting as a deep acceptor, which might give rise to conventional yellow luminescence and current collapse of GaN-based high electron mobility transistors (HEMTs). This was confirmed by photoluminescence (PL) spectra that the integrated intensity of yellow luminescence (YL) band was largely dependent on C incorporation. Therefore, we speculated that hole trap H1 might be responsible for a broad YL band in the samples.

Immunosensors Based on Graphene Field-Effect Transistors Fabricated Using Antigen-Binding Fragment

Abstract: To realize the antigen-antibody reaction for specific protein sensing using graphene field-effect transistors (G-FETs), the antigen-binding fragment (Fab), which is a component of conventional antibodies, was functionalized onto the graphene channel surface. Since the height of the Fab is approximately 3 nm, the antigen-antibody reaction is expected to occur inside the electrical double layer in the buffer solution. After functionalization of Fab onto the G-FET, the transfer characteristics shifted in the positive gate-voltage direction, indicating that the Fab was successfully modified onto the graphene surface. Then, the drain current changed after injecting the target proteins, and the dissociation constant was estimated to be 2.3 nM from the concentration dependence. These results indicate that the Fab-modified G-FETs have high potentials as highly sensitive biological sensors fabricated on the basis of the antigen-antibody reaction.

Present Status and Future Perspective of Bismuth-Based High-Temperature Superconducting Wires Realizing Application Systems

Abstract: Among a series of high-temperature superconducting materials that have been discovered to date, (Bi,Pb)2Sr2Ca2Cu3O10-x is the best candidate for superconducting wires that are long with commercial productivity, and critical current performance. In particular, the controlled overpressure (CT-OP) sintering technique gave us a 100% density of (Bi,Pb)2Sr2Ca2Cu3O10-x portion, which leads to robustness, increase in critical current, and mechanical tolerance. Many application prototypes are already verified and are being evaluated worldwide. Current leads for large magnets and magnetic billet heaters are already commercial products. Commercial applications for power cables, motors for ship propulsion and electric vehicles, and many kinds of magnets are promising in the near future.

Towards the Realization of Higher Connectivity in MgB$_{2}$ Conductors:In-situor SinteredEx-situ?

Abstract: The two most common types of MgB2 conductor fabrication technique – in-situ and ex-situ – show increasing conflicts concerning the connectivity, an effective current-carrying cross-sectional area. An in-situ reaction yields a strong intergrain coupling with a low packing factor, while an ex-situ process using pre-reacted MgB2 yields tightly packed grains, however, their coupling is much weaker. We studied the normal-state resistivity and microstructure of ex-situ MgB2 bulks synthesized with varied heating conditions under ambient pressure. The samples heated at moderately high temperatures of ~900 °C for a long period showed an increased packing factor, a larger intergrain contact area and a significantly decreased resistivity, all of which indicate the solid-state self-sintering of MgB2. Consequently the connectivity of the sintered ex-situ samples exceeded the typical connectivity range 5–15% of the in-situ samples. Our results show self-sintering develops the superior connectivity potential of ex-situ MgB2, though its intergrain coupling is not yet fulfilled, to provide a strong possibility of twice or even much higher connectivity in optimally sintered ex-situ MgB2 than in in-situ MgB2.

Mechanical Flexibility of ZnSnO/Ag/ZnSnO Films Grown by Roll-to-Roll Sputtering for Flexible Organic Photovoltaics

Abstract: The mechanical flexibility of ZnSnO (ZTO)/Ag/ZTO multilayer films prepared on flexible poly(ethylene terephthalate) (PET) substrates by roll-to-roll (R2R) sputtering was investigated for use in cost-efficient flexible organic solar cells (FOSCs). The change of resistance (ΔR) of the ZTO/Ag/ZTO films was measured by means of lab-made outer/inner bending, twist bending, and stretching test systems. The failure bending radii of the ZTO/Ag/ZTO film in the outer and inner bending tests were 3 and 4.5 mm, respectively. In addition, the twisting test showed that the resistance of the ZTO/Ag/ZTO multilayer began to increase at an angle of 38°. Furthermore, the stretching test showed that the strain failure of the ZTO/Ag/ZTO multilayer film was 3%. The superior flexibility of the ZTO/Ag/ZTO films is attributed to the existence of a ductile Ag layer and the mechanical stability of the amorphous ZTO film. Similar performances of the FOSCs with flexible ZTO/Ag/ZTO anodes to reference OSCs with ITO anodes indicate that the R2R sputter-grown ZTO/Ag/ZTO multilayer is promising as an indium-free flexible anode for cost-efficient FOSCs.