ITO Layer Research Articles

Hybrid Ag Nanowire–ITO as Transparent Conductive Electrode for Pure Sulfide Kesterite Cu2ZnSnS4 Solar Cells

We present the hybrid silver nanowire network–ultrathin ITO as the transparent conductive electrode for earth-abundant and environmentally friendly pure sulfide Cu2ZnSnS4 solar cells, replacing the scarce and expensive ITO. For this new hybrid transparent electrode, sputtered intrinsic zinc oxide is introduced as an antireflective coating replacing MgF2 in traditional Cu2ZnSnS4 solar cells. Random arrays of silver nanowire network with different densities hybridized with 20 nm ITO layer are employed in Cu2ZnSnS4 devices and their device performance is compared with the reference device with conventional ITO electrode. The devices with the hybrid electrodes with similar sheet resistance to ITO show generally improved current density due to their better optical transparency than ITO while maintaining similar fill factor. Cu2ZnSnS4 devices with low density Ag nanowire hybrid electrode give the highest efficiency of 6.4% on average mainly due to improved current density, among which the highest efficiency va...

Electrooptical effect in the plasmon structure glass–In2O3: Sn–ferroelectric–Al with a subwavelength grating

The spectral features of the electrooptical effect, in which an applied voltage changes the refractive index of a ferroelectric copolymer, are studied. Three nanostructures are investigated: two nanostructures play an auxiliary role, and the basic structure consists of a glass substrate, a transparent ITO (In2O3: Sn) layer, active copolymer layer, and an Al layer with a nanograting. This grating with a period of 400 nm meets the conditions of excitation of plasmon resonances. The light transmission coefficients of all structures are analyzed in the spectral range 400–900 nm. The transmission spectra have two characteristic plasmon dips, one of which is related to the copolymer–ITO interface and the other, to the copolymer–Al interface. The aluminum and ITO layers play the role of electrodes, which supply voltage pulses (from 0 to 15 V) to the copolymer layer. When studying the electrooptical effect, we detected spectral shifts in plasmon resonance bands when the amplitudes of both positive and negative voltage pulses (quadratic effect) increase. These shifts change the effective refractive indices (n eff) of the structural elements, reaching the minimum negative increment Δeff =–0.06.

Controlling surface contamination issues in the fabrication environment of high efficiency crystalline silicon-based homojunction solar cells

A procedure combining electrical measurements (determination of the implied Voc) and chemical analyses (VPD-ICP-MS) is presented, for the assessment of the wafer surface contamination in a clean room environment, and the identification of the critical elements regarding the fabrication of high efficiency crystalline Si-based homojunction cells. By applying the developed characterization procedure, we highlighted that the daily use of a PVD equipment for the deposition of ITO layers, can induce cross contamination issues, critical for the fabrication of high efficiency crystalline Si-based homojunction solar cells. We showed in this particular case that the degraded performances were due to surface contaminations by In and/or Sn. More precisely for the studied passivation procedure (firing of SiNx:H coated wafers) In and / or Sn would strongly affect the i-Voc (i-Voc<640 mV) when their surface concentrations exceed 1012 cm-2.

Modulating Hole Transport in Multilayered Photocathodes with Derivatized p-Type Nickel Oxide and Molecular Assemblies for Solar-Driven Water Splitting.

For solar water splitting, dye-sensitized NiO photocathodes have been a primary target. Despite marginal improvement in performance, limitations remain arising from the intrinsic disadvantages of NiO and insufficient catalysis. We report here a new approach to modifying NiO photocathodes with doped NiO bilayers and an additional layer of macro-mesoporous ITO. The trilayered electrode is functionalized with a surface-attached ruthenium polypyridyl dye and a covalently bridged nickel-based hydrogen evolution catalyst. The NiO film, containing a 2% K+-doped NiO inner layer and a 2% Cu2+-doped NiO outer layer, provides sufficient driving force for hole transport following hole injection by the molecular assembly. Upon light irradiation, the resulting photocathode generates hydrogen from water sustainably with enhanced photocurrents and a Faradaic efficiency of ∼90%. This approach highlights the value of modifying both the internal and surface structure of NiO and provides insights into a new generation of dye-sensitized photocathodes for solar-driven water splitting cells.

Fabrication of Hybrid Polymer Solar Cells By Inverted Structure Based on P3HT:PCBM Active Layer

Hybrid polymer solar cell has privilege than its conventional structure, where it usually has structure of (ITO/PEDOT:PSS/Active Layer/Al). In humid environment the PEDOT:PSS will absorb water and hence can easily etch the ITO. Therefore it is necessary to use an alternative method to avoid this drawback and obtain more stable polymer solar cells, namely by using hybrid polymer solar cells structure with an inverted device architecture from the conventional, by reversing the nature of charge collection. In this paper we report the results of the fabrication of inverted bulk heterojunction polymer solar cells based on P3HT:PCBM as active layer, utilizing ZnO interlayer as buffer layer between the ITO and active layer with a stacked structure of ITO/ZnO/P3HT:PCBM/PEDOT:PSS/Ag. The ZnO interlayer is formed through short route, i.e. by dissolving ZnO nanoparticles powder in chloroform-methanol solvent blend rather than by sol-gel process. Based on the measurement results on electrical characteristics of inverted polymer solar cells under 500 W/m2 illumination and AM 1.5 direct filter at room temperature, cell with annealing process of active layer at 110 °C for 10 minutes results in higher cell performance than without annealing, with an open-circuit voltage of 0.21 volt, a short-circuit current density of 1.33 mA/cm2 , a fill factor of 43.1%, and a power conversion efficiency of 0.22%. The low cell’s performance is caused by very rough surface of ZnO interlayer.

Highly (001)-Textured Tetragonal BiFeO3 Film and Its Photoelectrochemical Behaviors Tuned by Magnetic Field.

Highly (001)-textured BiFeO3 film in tetragonal phase (T-BFO) with a giant c/a ratio was first obtained on quartz/polycrystalline ITO substrate. Our results indicate that the polycrystalline ITO layer with small surface roughness is a critical point to control the growth of T-BFO structure. It should be ascribed to the fact that a Bi-rich phase interlayer (∼5 nm) could be formed on ITO, which acted as a crystal seed layer and thus induced the growth of (001)-textured T-BFO structure. The observed weak room temperature ferromagnetism should be attributed to Fe valence change. Open circuit potential measurements under 360 μW/cm2 full spectra irradiation show that the open circuit potential and the lifetime of photo-induced carriers increased under applied magnetic field, which reveals that the applied magnetic field can manipulate the photo electrochemical behaviors of BFO film. Our findings offer a simple way to fabricate highly (001)-textured T-BFO film, which make it desirable to obtain extensive applications for these oriented BFO films.

Highly Selective Solar Thermal Sprayable Coating Based on Carbon Nanotubes

A key component in solar thermal energy conversion system is the light collector that is coated with an absorbing material. Optimal performance is accomplished by high absorptance and low emittance. The best collectors are fabricated by vacuum deposition processes, which are limited to small size and flat objects. Here, the formation and performance of a new three-layer solar selective coating, which is formed by a simple wet-deposition process is reported. The solar absorbing layer is based on carbon nanotubes, which are considered the most absorbing material. This layer is coated by a second layer of ITO, which functions as an IR reflecting layer, followed by an AlOOH anti-reflective layer. The resulting CNT/ITO/AlOOH coating exhibited the best-reported spectral selectivity by wet deposition process, with high absorptance of 0.941 ± 0.004 and low emittance of 0.13 ± 0.02 at room temperature. Furthermore, the multilayer sprayable coating is stable at elevated temperature for a prolong time and therefore, shows promise for application in large scale and on-site solar thermal facilities.

The role of ITO resistivity on current spreading and leakage in InGaN/GaN light emitting diodes

The effect of a transparent ITO current spreading layer on electrical and light output properties of blue InGaN/GaN light emitting diodes (LEDs) is discussed. When finite conductivity of ITO is taken into account, unlike in previous models, the topology of LED die and contacts are shown to significantly affect current spreading and light output characteristics in top emitting devices. We propose an approach for calculating the current transfer length describing current spreading. We show that an inter-digitated electrode configuration with distance between the contact pad and the edge of p-n junction equal to transfer length in the current spreading ITO layer allows one to increase the optical area of LED chip, as compared to the physical area of the die, light output power, and therefore, the LED efficiency for a given current density. A detailed study of unpassivated LEDs also shows that current transfer lengths longer than the distance between the contact pad and the edge of p-n junction leads to increasing surface leakage that can only be remedied with proper passivation.

Tetrathiafulvalene derivative as a new hole-transporting material for highly efficient perovskite solar cell

Hole-transporting materials play an important role in perovskite solar cells. In this study, we introduced a novel hole-transporting material without p-type dopant, a tetrathiafulvalene derivative anchored with eight carboxyl groups (TTA) into inverted structure perovskite solar cells. The devices with TTA as hole-transporting layer showed high power conversion efficiency of 16.7%, which was 44.5% improvement compared with the reference devices without hole-transporting layer. The performance improvement was ascribed to three factors: 1) the better match of energy level between ITO and perovskite layer; 2) enhanced hole extraction at anode interface; 3) improved perovskite morphology.

Fabrication and characteristics of excellent current spreading GaN-based LED by using transparent electrode-insulator-semiconductor structure**Project supported by the Natural Science Foundation of China (Nos. 61306051, 61306050) and the National High Technology Program of China (No. 2014AA032606).

GaN-based vertical light-emitting-diodes (V-LEDs) with an improved current injection pattern were fabricated and a novel current injection pattern of LEDs which consists of electrode-insulator-semiconductor (EIS) structure was proposed. The EIS structure was achieved by an insulator layer (20-nm Ta2O5) deposited between the p-GaN and the ITO layer. This kind of EIS structure works through a defect-assisted tunneling mechanism to realize current injection and obtains a uniform current distribution on the chip surface, thus greatly improving the current spreading ability of LEDs. The appearance of this novel current injection pattern of V-LEDs will subvert the impression of the conventional LEDs structure, including simplifying the chip manufacture technology and reducing the chip cost. Under a current density of 2, 5, 10, and 25 A/cm2, the luminous uniformity was better than conventional structure LEDs. The standard deviation of power density distribution in light distribution was 0.028, which was much smaller than that of conventional structure LEDs and illustrated a huge advantage on the current spreading ability of EIS-LEDs.

Fabrication of p-type SrCuSeF/n-type In2O3:Sn bilayer ohmic tunnel junction and its application to the back contact of CdS/CdTe solar cells

To develop polycrystalline thin-film tandem solar cells, a SrCuSeF/In2O3:Sn (ITO) bilayer film was studied. The transparent p-type conductive SrCuSeF layer was deposited by pulsed laser deposition (PLD), and the n-type conductive ITO layer was deposited by RF sputtering. The SrCuSeF/ITO bilayer film showed ohmic I–V characteristics. A tunnel junction between the p-type SrCuSeF and n-type ITO layers was successfully formed because the p-type SrCuSeF and the n-type ITO layers had sufficiently high carrier concentrations. The SrCuSeF/ITO bilayer film was applied as the back contact of a CdS/CdTe solar cell. The photovoltaic performance of the CdS/CdTe solar cell depends considerably on the thickness of the SrCuSeF layer. The CdTe solar cell with a back contact of the SrCuSeF layer with a thickness of 34 nm and the ITO layer with a thickness of 200 nm showed a high conversion efficiency of 14.3% (VOC = 804 mV, JSC = 27.5 mA/cm2, and FF = 0.65). The conversion efficiency was much higher than that of the CdTe solar cell with the SrCuSeF single-layer back contact (11.6%) and that of the CdTe cell with the ITO single-layer back contact (2.75%).

A forming-free bipolar resistive switching behavior based on ITO/V2O5/ITO structure

Forming-free bipolar resistive switching behavior in an ITO/V2O5/ITO structure is observed. While the bottom ITO layer functions as a common ground electrode, the top ITO layer is an active element and used as an oxygen reservoir, with an additional metal electrode patterned on its top for making contact. In contrast to typical metal/transition metal oxide/metal based resistive memories, our device exhibits a low resistance state in its virgin state and is switched to a high resistance state when a forward bias of ∼+2.5 V is applied. The device can be reset to its original state at a reverse bias of ∼–1.5 V. A noticeable decrease in switching voltage with a reduced top contact area is observed, indicating a strong electric field enhanced switching mechanism. Different from the widely seen conductive filament mechanism in bipolar switching, we explain the switching behavior by the migration of oxygen ions at the top ITO/V2O5 interface. When oxygen ions are extracted to the ITO side, an interfacial layer with reduced oxidation states is formed and acts as a Schottky barrier that suppresses the current through the whole device. The results suggest future applications in low power, high speed integrated non-volatile memories.

Negative bias illumination stress instability in amorphous InGaZnO thin film transistors with ITO local conducting buried layer

The investigations on the device instabilities of amorphous InGaZnO thin film transistors (a-IGZO TFTs) with ITO local conducting buried layer (LCBL) under the source/drain region and in the middle of the active channel region have been performed under negative bias and illumination stress. From the increased drain current of a-IGZO with ITO LCBL, one can control the drive current by modulating the length of ITO LCBL without changing the ratio of channel width and length. The reason for the less degradation of a-IGZO TFTs with LCBL under negative bias stress than that of device without LCBL was explained by the fact that ITO LCBL could act to reduce the effective energy barrier and act as a hole damping layer. However, the device degradation of a-IGZO with ITO LCBL under negative bias and illumination stress was more significant than that of one without LCBL due to the electron hole pair generation in ITO layer under illumination.

The lateral photovoltaic effect in ITO/Si(n) heterojunction

The ITO/Si heterojunction has been studied as a solar cell longtime ago, but seldom done on the lateral photovoltaic effect (LPE). In this paper, we reported a new finding of lateral photovoltaic effect (LPE) in the ITO/Si(n) heterojunctions. The ITO films were prepared directly on the n-type single crystal Si substrate with different thicknesses by magnetron reactive sputtering technology. When we measured the lateral photovoltages in the ITO/Si structures as a function of laser position under illumination of different laser powers and different laser wavelengths, it was found that the LPE increased with both laser power and laser wavelength, which can be ascribed to the increased number of electron-hole pairs resulting from the increased laser power for a constant laser wavelength or the increased laser wavelength for a constant laser power. Moreover, the position sensitivity decreased dramatically with increasing the thickness of ITO thin films, but the nonlinearity seems to be improved gradually, both of which can be successfully explained by the increased carrier diffusion length induced by the decreased resistivity of ITO layer. The ITO/Si(n) heterojunction possesses good position sensitivity and suitable nonlinearity simultaneously when the thickness of ITO layer is 15 nm. Our results may provide important insight that one can obtain a suitable LPE in the ITO/Si(n) heterojunction with higher position sensitivity and lower nonlinearity by controlling the thickness of the ITO thin films, and also suggest that the ITO/Si(n) heterojunction is a potential candidate for developing novel and multifunctional optical sensors.

Effect of TiO2 modification with amino-based self-assembled monolayer on inverted organic solar cell

The effects of surface modification of titanium dioxide (TiO2) on the performance of inverted type organic solar cells (i-OSCs) was investigated in this study. A series of benzoic acid derivatized self-assembled monolayer (SAM) molecules of 4′-[(hexyloxy)phenyl]amino-3,5-biphenyl dicarboxylic acid (CT17) and 4′-[1-naphthyl (phenyl)amino]biphenyl-4-carboxylic acid (CT19) were utilized to modify the interface between TiO2 buffer layer and poly-3 hexylthiophene (P3HT):[6,6]-phenyl C61 butyric acid methyl ester (PC61BM) active layer having the device structure of ITO/TiO2/SAM/P3HT:PC61BM/MoO3/Ag. The work function and surface wetting properties of TiO2 buffer layer served as electron transporting layer between ITO and PC61BM active layer were tuned by SAM method. The solar cell of the SAM modified devices exhibited better performance. The power conversion efficiency (PCE) of i-OSCs devices with bare TiO2 electrodes enhanced from 2.00% to 2.21% and 2.43% with CT17 and CT19 treated TiO2 electrodes, respectively. The open circuit voltage (Voc) of the SAM treated TiO2 devices reached to 0.60V and 0.61V, respectively, while the Voc of untreated TiO2 was 0.57V. The water contact angle of i-OSCs with CT17 and CT19 SAMs was also higher than the value of the unmodified TiO2 electrode. These results show that inserting a monolayer at the interface between organic and inorganic layers is an useful alternative method to improve the performance of i-OSCs.

The high-frequency tunnel capacitance overload phenomenon of semiconductor-insulator-semiconductor heterojunction caused by the ultra-thin interfacial layers

The SIS (semiconductor-insulator-semiconductor) structure heterojunction derived from the MOS (metal-oxide- semiconductor) devices, and inherit the advantages of low cost, simple structure, stable performance and high theoretical efficiency, which drew tons of attention for solar cell and integrated circuit applications researches. SIS device consist of TCO (transparent conduction oxide) layer, ultra-thin oxide layer and silicon substrate, in which the carriers can tunnel through the oxide layer when the thickness of the interface oxide layer is reduced to 1–5 nm. Inside the SIS solar cell, the ultra-thin passivation layer has multiple functions including tunneling contact and buffer the crystalline lattice mismatch. Capacitance reflects a device’s ability to charge and discharge, and the capacitance voltage ( CV ) characteristic is critical in the estimate of the passivation quality no matter in the high-low frequency method or DLTS (deep level transient spectroscopy system) method, and the passivation quality manifest as interface state density ( D it). When examining the high frequency (1 MHz) CV characteristic of the SIS which was fabricated by depositing ITO upon n-type silicon directly by RF magnetron sputtering, it is found that once the applied voltage ( V g) exceeds a certain value V T (tunneling voltage), the differential capacitance value of the device would far beyond the range of the instrument and tends to infinity, which can be summarized as tunnel capacitance overload phenomenon (TCOP). As the description and explanation of this phenomenon have not been found in previous studies, the high-frequency TCOP of the SIS heterojunction with ultra-thin interfacial layers was investigated in details in this paper. The current-voltage characteristics of the SIS devices were obtained from the solar simulator and shown good photovoltaic conversion efficiency. The built-in electric field of the SIS with different ITO thickness was obtained by fitting the CV curves, which was measured by the Keysight E4980A CV system. The XPS depth profiling showed that the composition and percentage content of the interface, including In, Sn, O, Si, and the oxide silicon compound of Si2O, SiO, Si2O3, SiO2 which can be summed as SiO x (1≤ x ≤2). The TEM images showed that the thickness of the SiO x layer increases with the thickness of ITO layer, and the V T in TCOP is apparently linked to the SiO x thickness. When the applied V g exceed V T, a huge amount of electrons would enter the E C of the silicon surface, unlike the MOS with thick and well passivated insulator layer, the ultra-thin SiO x layer can’t hold these mass of electrons at the SIS interface, so the electrons would directly tunnel through the SiO x into the ITO layer and the TCOP appears. Capacitance voltage characteristics are critical for estimating the properties of heterojunction interfaces, and high frequency CV is indispensable for measuring the D it. The existence of the TCOP is the main reason why other methods which based on the CV characteristics are difficult to estimate the interface state. But from another point of view, the TCOP is repeatable in the same device, which implied that the solar cells that fabricated by the directly depositing ITO thin films on n-type silicon is stable.

Tunable Magneto-Optical Kerr Effects of Nanoporous Thin Films

Magnetoplasmonics, combining magnetic and plasmonic functions, has attracted increasing attention owing to its unique magnetic and optical properties in various nano-architectures. In this work, Ag, CoFeB and ITO layers are fabricated on anodic aluminum oxide (AAO) porous films to form hybrid multi-layered nanoporous thin films by magnetron sputtering deposition process. The designed nanostructure supports localized surface plasmon resonance (LSPR) and tunable magneto-optical (MO) activity, namely, the sign inversion, which can be controlled by AAO porous film geometry (pore diameter and inter-pore spacing) flexibly. The physical mechanism of this special MO phenomena is further analyzed and discussed by the correlation of Kerr rotation and electronic oscillations controlled by the surface plasmon resonance that is related to the nanoporous structure.

Growth Direction Control of ZnO Nanorods on the Edge of Patterned Indium–Tin Oxide/Aluminum-Doped Zinc Oxide Bilayers

ZnO nanorods were grown on the edge of patterned indium–tin oxide/aluminum-doped zinc oxide (ITO/AZO) bilayers by a hydrothermal method. Since the mask ITO layer covered the AZO seed layer, the ZnO nanorods grew radially on the edge of the AZO seed layer. By etching the as-patterned ITO/AZO bilayers with dilute HCl solution, the under-cut space is created under the ITO layer. We found that the under-cut space is the key for the vertical growth direction of ZnO nanorods on the etched-edge of the AZO seed layer. Only the ZnO nuclei phase exactly in parallel to the substrate can extend out from the under-cut space and provides the (0002) plane for the growth of the vertical ZnO nanorods. Interestingly, we found that the ZnO nanorods grew laterally on the etched-edge of the patterned ITO/AZO bilayers prepared with 400 °C substrate temperature. Due to the higher crystallinity of the AZO seed layer (400 °C), the etched-edge microstructure is different from that of the AZO seed layers prepared at room temperatur...

It Takes Two to Tango-Double-Layer Selective Contacts in Perovskite Solar Cells for Improved Device Performance and Reduced Hysteresis.

Solar cells made from inorganic-organic perovskites have gradually approached market requirements as their efficiency and stability have improved tremendously in recent years. Planar low-temperature processed perovskite solar cells are advantageous for possible large-scale production but are more prone to exhibiting photocurrent hysteresis, especially in the regular n-i-p structure. Here, a systematic characterization of different electron selective contacts with a variety of chemical and electrical properties in planar n-i-p devices processed below 180 °C is presented. The inorganic metal oxides TiO2 and SnO2, the organic fullerene derivatives C60, PCBM, and ICMA, as well as double-layers with a metal oxide/PCBM structure are used as electron transport materials (ETMs). Perovskite layers deposited atop the different ETMs with the herein applied fabrication method show a similar morphology according to scanning electron microscopy. Further, surface photovoltage spectroscopy measurements indicate comparable perovskite absorber qualities on all ETMs, except TiO2, which shows a more prominent influence of defect states. Transient photoluminescence studies together with current-voltage scans over a broad range of scan speeds reveal faster charge extraction, less pronounced hysteresis effects, and higher efficiencies for devices with fullerene compared to those with metal oxide ETMs. Beyond this, only double-layer ETM structures substantially diminish hysteresis effects for all performed scan speeds and strongly enhance the power conversion efficiency up to a champion stabilized value of 18.0%. The results indicate reduced recombination losses for a double-layer TiO2/PCBM contact design: First, a reduction of shunt paths through the fullerene to the ITO layer. Second, an improved hole blocking by the wide band gap metal oxide. Third, decreased transport losses due to an energetically more favorable contact, as implied by photoelectron spectroscopy measurements. The herein demonstrated improvements of multilayer selective contacts may serve as a general design guideline for perovskite solar cells.

Fully transparent high performance thin film transistors with bilayer ITO/Al-Sn-Zn-O channel structures fabricated on glass substrate

In this work, fully transparent high performance double-channel indium-tin-oxide/Al–Sn–Zn–O thin-film transistors (ITO/ATZO TFTs) are successfully fabricated on glass by radio frequency (RF) magnetron sputtering. The ITO layer acts as the bottom channel layer to increase the channel carrier concentration. The top ATZO channel layer, which is deposited via high oxygen partial pressure in the sputtering process, is useful to control the minimum off-state current. After annealing, the ITO/ATZO TFT demonstrates outstanding electrical performances, including a high ON/OFF current ratio (Ion/Ioff) of 3.5 × 108, a steep threshold swing (SS) of 142.2 mV/decade, a superior saturation mobility (μsat) of 246.0 cm2/Vs, and a threshold voltage VT of 0.5 V. The operation mechanisms for double-channel structures are also clarified.