ITO Contact Research Articles

Optically transparent highly conductive contact based on ITO and copper metallization for solar cells

This paper presents the results of obtaining and studying the electrical and optical characteristics of an optically transparent highly conductive Ni/Cu/Ti/ITO contact in order to reduce electrical resistance losses on the front side of the silicon solar cell. The topology of the contact metallization is a square 50 × 50 mm2 with an interdigitated electrode structure. A Ni/Cu/Ti contact metallization formed on ITO layer reduces the surface resistance by more than 60 times. It has been shown that the use of a Ni/Cu/Ti contact with a finger thickness of at least 1.5 μm and a width of 17 μm was formed is a good alternative to traditional contacts for silicon solar cells based on silver paste.

Comparison of TJ and ITO GaN VCSELs in terms of their frequency characteristics

The work focuses on vertical cavity surface emitting lasers (VCSELs) made of nitride materials that emit a wavelength of 445 nm. Two structures were examined: a laser with a tunnel junction and implantation (TJ VCSEL) and an ITO contact (ITO VCSEL). The analysis delves into capacitance phenomena influencing the modulation speed of these lasers. The results highlight differences in active currents between two structures, i.e., currents which contribute to the modulation of the laser emission. According to the authors’ simulations, the TJ VCSEL is more effective in modulating the number of carriers in the active region than the ITO VCSEL, assuming the same modulation amplitude of driving current.

Enhanced LWIR response of InP/InAsP quantum discs-in-nanowire array photodetectors by photogating and ultra-thin ITO contacts

Here we report on an experimental and theoretical investigation of the long-wavelength infrared (LWIR) photoresponse of photodetectors based on arrays of three million InP nanowires with axially embedded InAsP quantum discs. An ultra-thin top indium tin oxide contact combined with a novel photogating mechanism facilitates an improved LWIR normal incidence sensitivity in contrast to traditional planar quantum well photodetectors. The electronic structure of the quantum discs, including strain and defect-induced photogating effects, and optical transition matrix elements were calculated by an 8-band k·p simulation along with solving drift-diffusion equations to unravel the physics behind the generation of narrow linewidth intersubband signals observed from the quantum discs.

Optical loss analysis of Sb2S3 and Sb2Se3 thin film solar cells: A Quantitative Assessment

Optical loss either by light reflection, or light absorption in different layers of a solar cell, can significantly impact short-circuit current density. In this paper, an optical model has been developed to analyze the optical loss in thin film solar cells made of CdS/Sb2S3 or CdS/Sb2Se3 antimony chalcogenide. This model is based on optical loss from absorption in thin layers and reflection at the interfaces of glass/TCO/CdS/(Sb2S3 or Sb2Se3) only by considering the optical properties of layers (refractive index and extinction coefficient). The transmission and reflection rate of Sb2S3 or Sb2Se3 show almost a similar trend. The absorptivity and relative loss in short-circuit current density (Jsc) versus the thickness of Sb2S3 and Sb2Se3 layers was calculated for two different structures: glass/TCO/CdS/Sb2S3 and glass/TCO/CdS/Sb2Se3. The Sb2Se3 solar cell shows a slightly better conversion performance compared to Sb2S3 solar cell due to lower reflection loss. The light reflection was calculated at four interfaces. The transmission rate of light through TCO, ITO, and CdS layers was calculated to obtain an optimal thickness for these layers. TCO showed a higher transmission rate and thus is preferred in antimony solar cell structures. The variations of (Jsc) and loss for Jsc with different thicknesses of ITO (>20%) or TCO (<20%) contact layers, favoring TCO for its lower optical losses and higher Jsc (24 mA cm−2).

Direct Integration of Perovskite Solar Cells with Carbon Fiber Substrates.

Integrating photovoltaic devices onto the surface of carbon-fiber-reinforced polymer substrates should create materials with high mechanical strength that are also able to generate electrical power. Such devices are anticipated to find ready applications as structural, energy-harvesting systems in both the automotive and aeronautical sectors. Here, the fabrication of triple-cation perovskite n-i-p solar cells onto the surface of planarized carbon-fiber-reinforced polymer substrates is demonstrated, with devices utilizing a transparent top ITO contact. These devices also contain a "wrinkled" SiO2 interlayer placed between the device and substrate that alleviates thermally induced cracking of the bottom ITO layer. Devices are found to have a maximum stabilized power conversion efficiency of 14.5% and a specific power (power per weight) of 21.4Wg-1 (without encapsulation), making them highly suitable for mobile power applications.

Effects of ITO Contact Sizes on Performance of Blue Light MicroLEDs

In this study, the effect of ITO contact ratio for blue light micro-light-emitting diode (µLED) with dimensions 40 μm × 40 μm was assessed. The contact ratio from 0.2 to 0.8 was designed for the ratio of electrode area to light-emitting area. As the contact ratio increased from 0.2 to 0.8, the turn-on voltage of µLED decreased. It could be due to the short lateral diffusion length in multiple quantum wells (MQW) and lower parallel resistance for the µLED with a large contact ratio. The leakage currents of single µLED were below 5.1 × 10–9 A, no matter the contact ratio. It means that the contact ratio does not affect the leakage current as measured on single chip. Moreover, µLED array with a 0.8 contact ratio presented the highest output power than other samples (5.25 mW as the current density of 1875 A/cm2). It could attribute to the MQWs usage, the metal contact reflective behavior and less current crowding, which generated more carriers and extracted more lighting from the µLED. The simulation data using SpeCLED software agreed well with these experiments, and µLED with a 0.8 contact ratio showed the best optoelectronic properties.

Raytracing Modelling of Infrared Light Management Using Molybdenum Disulfide (MoS2) as a Back-Reflector Layer in a Silicon Heterojunction Solar Cell (SHJ).

The silicon heterojunction solar cell (SHJ) is considered the dominant state-of-the-art silicon solar cell technology due to its excellent passivation quality and high efficiency. However, SHJ’s light management performance is limited by its narrow optical absorption in long-wave near-infrared (NIR) due to the front, and back tin-doped indium oxide (ITO) layer’s free carrier absorption and reflection losses. Despite the light-trapping efficiency (LTE) schemes adopted by SHJ in terms of back surface texturing, the previous investigations highlighted the ITO layer as a reason for an essential long-wavelength light loss mechanism in SHJ solar cells. In this study, we propose the use of Molybdenum disulfide (MoS2) as a way of improving back-reflection in SHJ. The text presents simulations of the optical response in the backside of the SHJ applying the Monte-Carlo raytracing method with a web-based Sunsolve high-precision raytracing tool. The solar cells’ electrical parameters were also resolved using the standard electrical equivalent circuit model provided by Sunsolve. The proposed structure geometry slightly improved the SHJ cell optical current density by ~0.37% (rel.), and hence efficiency (η) by about 0.4% (rel.). The SHJ cell efficiency improved by 21.68% after applying thinner back ITO of about 30 nm overlayed on ~1 nm MoS2. The efficiency improvement following the application of MoS2 is tentatively attributed to the increased NIR absorption in the silicon bulk due to the light constructive interface with the backside components, namely silver (Ag) and ITO. Study outcomes showed that improved SHJ efficiency could be further optimized by addressing front cell components, mainly front ITO and MoS2 contact engineering.

Characterization of the Stability of Indium Tin Oxide and Functional Layers for Semitransparent Back‐Contact Applications on Cu(in,Ga)Se2Solar Cells

Herein, a detailed study of the stability of different ITO‐based back‐contact configurations (including bare ITO contacts and contacts functionalized with nanometric Mo, MoSe2, and MoS2layers) under the coevaporation processes developed for the synthesis of high‐efficiency Cu(In,Ga)Se2(CIGSe) solar cells is reported. The results show that bare ITO layers can be used as efficient back contacts for coevaporation process temperatures of 480 ºC. However, higher temperatures produce an amorphous In–Se phase at the ITO surface that reduces the contacts transparency in the visible region. This is accompanied by degradation of the solar cells’ efficiency. Inclusion of a Mo functional layer leads to the formation of a MoSe2interfacial phase during the coevaporation process, which improves the cells’ efficiency, achieving device efficiencies similar to those obtained with reference solar cells fabricated with standard Mo back contacts. Optimization of the initial Mo layer thickness improves the contact transparency, achieving contacts with an optical transparency of 50% in the visible region. This is accompanied by a relevant decrease in back reflectivity in the CIGSe devices, confirming the potential of these contact configurations for the development of semitransparent CIGSe devices with improved optical aesthetic quality without compromising the device performance.

CdS based chemiresistor with Schottky contact: Toxic gases detection with enhanced sensitivity and selectivity at room temperature

Surmounting the selectivity issue of gas sensors and detecting low ppm concentration of gases is highly significant for widespread deployments of sensors to build networks in applications including vehicular emission, fuel-based household appliances, and industrial emissions. Herein, a strategy is proposed to improve the selectivity and sensitivity of the cadmium sulfide (CdS) based sensor via changes in contact material by utilizing different metals. CdS was deposited via the SILAR method on three different glass substrates which have Au, ITO, and Ag contacts, respectively, through which Schottky barrier height (SBH) was adjusted between CdS and metal contact. CdS was thoroughly verified by structural and morphological characterization techniques. As-fabricated devices were tested, and gas sensing results suggest that Au and ITO contacts have significantly superior selectivity towards NO2 and CO gases over other gases. Further, experimental values reveal that sensors can detect up to 0.3 ppm and 1.25 ppm, respectively. Good selectivity can be attributed to the regulation of the SBH. Additionally, as-fabricated devices displayed good long-term stability and short response and recovery times. The present study may provide a rational design for fabricating a high-performance chemiresistive gas sensor for the detection of sub-ppm levels of hazardous gases present in the environment.

Memristor structure with the effect of switching resistance based on silicon nitride thin layers

The electrophysical properties and the resistive switching effect of the ITO/SiN x /Si memristor structure were studied. A silicon nitride film with a thickness of ~200 nm with an inhomogeneous element depth distribution was deposited by low-pressure chemical vapor deposition. Based on the Rutherford backscattering data, it was shown that the concentration of excess silicon atoms in the SiN x film increases from 9 to 44 % when approaching the Si substrate. The analysis of the current-voltage characteristics of ITO/SiN x /Si structures revealed that the conduction mechanism in the high-resistance state is determined by the nitride film properties and is described by the Poole-Frenkel model taking into account the hopping model of electron transport between traps. Switching to the low-resistance state is probably caused by the migration of indium or tin ions from the ITO contact to the SiN x layer. The conduction of the ITO/SiN x /Si structure in the low-resistance state is determined by both the mechanisms of charge-carrier injection from the contact and charge-carrier transport through the dielectric layer. Reverse polarity results in destructing the conductive channel and switching the structure to the high-resistance state. The photo-switching effect was found for the ITO/SiN x /Si structure, which opens up new possibilities of using memristors in silicon optoelectronic systems.

Emerging Photovoltaic (PV) Materials for a Low Carbon Economy

Emerging photovoltaic (PV) technologies have a potential to address the shortcomings of today’s energy market which heavily depends on the use of fossil fuels for electricity generation. We created inventories that offer insights into the environmental impacts and cost of all the materials used in emerging PV technologies, including perovskites, polymers, Cu2ZnSnS4 (CZTS), carbon nanotubes (CNT), and quantum dots. The results show that the CO2 emissions associated with the absorber layers are much less than the CO2 emissions associated with the contact and charge selective layers. The CdS (charge selective layer) and ITO (contact layer) have the highest environmental impacts compared to Al2O3, CuI, CuSCN, MoO3, NiO, poly (3-hexylthiophene-2,5-diyl (P3HT)), phenyl-C61-butyric acid methyl ester (PCBM), poly polystyrene sulfonate (PEDOT:PSS), SnO2, spiro-OMeTAD, and TiO2 (charge selective layers) and Al, Ag, Cu, FTO, Mo, ZnO:In, and ZnO/ZnO:Al (contact layers). The cost assessments show that the organic materials, such as polymer absorbers, CNT, P3HT and spiro-OMeTAD, are the most expensive materials. Inorganic materials would be more preferable to lower the cost of solar cells. All the remaining materials have a potential to be used in the commercial PV market. Finally, we analyzed the cost of PV materials based on their material intensity and CO2 emissions, and concluded that the perovskite absorber will be the most eco-efficient material that has the lowest cost and CO2 emissions.

Boosting ultrathin aSi-H solar cells absorption through a nanoparticle cross-packed metasurface

Hydrogenated amorphous silicon (a-Si:H) solar cells have some performance limitations related to the mobility and lifetime of their carriers. For this reason, it is interesting to explore thin-film solutions, achieving a tradeoff between photons optical absorption and the electrical path of the carriers to get the optimum thickness. In this work, we propose the insertion of a metasurface based on a cross-patterned ITO contact film, where the crosses are filled with nanospheres. We numerically demonstrate that this configuration improves the photogenerated current up to a 40% by means of the resonant effects produced by the metasurface, being independent on the impinging light polarization. Light handling mechanisms guide light into the active and auxiliary layers, increasing the effective absorption and mitigating the Staebler-Wronski effect. The selection of optimum materials and parameters results in nanospheres of ZnO with a 220 nm radius.

Development and research carbon nanotube-based resistive gas sensor

Experimental studies of the processes of formation of catalytic centres (CC) and carbon nanotubes (CNTs) at ITO contacts have been carried out. The regularities of the influence of the annealing temperature on the geometric dimensions of CC have been established. An array of interwoven CNTs with a highly developed surface has been grown. A model of a gas sensor with a sensitive element based on a CNT network has been created. The reaction time and reaction of the sensor, its sensitivity to N2, O2, and Ar have been experimentally investigated. It has been shown that the sensor has a maximum sensitivity of 17.2% to N2, 16.3% to Ar, and 18.7% to O2 in the range of gas concentrations from 30 to 70 ppm. It has been shown that gas detection is possible at room temperature, despite a rather long reaction and reduction time. In this case, an almost complete restoration of the sensitive element of the initial resistance has occurred without additional heating.

Influence of Resonator Length on Performance of Nitride TJ VCSEL

This paper presents computer simulations of nitride-based tunnel-junction (TJ) vertical-cavity surface emitting lasers (VCSELs). The analyzed structures are non-polar continuous wave VCSELs with dielectric distributed Bragg reflectors (DBRs) emitting at around 405 nm. Both electric contacts are in the form of rings that surround the DBRs. The bottom electric contact also acts as a thermal contact between the laser and the heat sink, because the dielectric DBR is a thermal insulator. The results of our study show that the thickness of the laser's resonator and its absorption coefficient each have a very strong impact on both the threshold current and emitted power. A thick resonator reduces the thermal resistance of the device, but increases the optical absorption. The optimal resonator thickness depends on the absorption coefficient of the resonator material, different possible values for which are investigated here. Moreover, VCSELs with TJs has been compared with similar devices, with semi-transparent ITO contacts and without a TJ.

P‐13.8: Influences of Passivation Hole Etching on the ITO and Metal Contact for Bottom Emission AMOLED Display

A top‐gate self‐aligned a‐IGZO TFT backplate with white OLED and color filter was demonstrated in this paper. Three kind of PV (passivation) hole etching sequences noted as case 1~3, were studied to verify the contact between ITO and Source/Drain electrode. For case 3, PV hole etching process after PLN patterning shows smooth metal surface and excellent panel performance. In contrast, Sourse and Drain metal corrosion occurred due to non‐uniform PV film deposition in other two cases , resulting in bad contact between ITO and S/D metal and poor panel performance.

Efficient tunnel junction contacts for high-power semipolar III-nitride edge-emitting laser diodes

We demonstrate high-power edge-emitting laser diodes (LDs) with tunnel junction contacts grown by molecular beam epitaxy (MBE). Under pulsed conditions, lower threshold current densities were observed from LDs with MBE-grown tunnel junctions than from similarly fabricated control LDs with ITO contacts. LDs with tunnel junction contacts grown by metal-organic chemical vapor deposition (MOCVD) were additionally demonstrated. These LDs were fabricated using a p-GaN activation scheme utilizing lateral diffusion of hydrogen through the LD ridge sidewalls. Secondary ion mass spectroscopy measurements of the [Si] and [Mg] profiles in the MBE-grown and MOCVD-grown tunnel junctions were conducted to further investigate the results.

Fabrication and Characterization of AlGaN-Based UV LEDs with a ITO/Ga₂O₃/Ag/Ga₂O₃ Transparent Conductive Electrode.

We fabricated a complex transparent conductive electrode (TCE) based on Ga2O3 for AlGaN-based ultraviolet light-emitting diodes. The complex TCE consists of a 10 nm ITO, a 15 nm Ga2O3, a 7 nm Ag, and a 15 nm Ga2O3, forming a ITO/Ga2O3/Ag/Ga2O3 multilayer. The metal layer embedded into Ga2O3 and the thin ITO contact layer improves current spreading and electrode contact properties. It is found that the ITO/Ga2O3/Ag/Ga2O3 multilayer can reach a 92.8% transmittance at 365 nm and a specific contact resistance of 10−3 Ω·cm2 with suitable annealing conditions.

Above 10% efficiency earth-abundant Cu2ZnSn(S,Se)4 solar cells by introducing alkali metal fluoride nanolayers as electron-selective contacts

The present investigation mainly addresses the open circuit voltage (Voc) issue in kesterite based Cu2ZnSn(S,Se)4 solar cells by simply introducing alkali metal fluoride nanolayers (~ several nm NaF, or LiF) to lower the work functions of the front ITO contacts without conventional hole-blocking ZnO layers. Kelvin probe measurements confirmed that the work function of the front ITO decreases from 4.82 to 3.39 and 3.65 eV for NaF and LiF, respectively, resulting in beneficial band alignment for electron collection and/or hole blocking on top electrodes. Moreover, a 10.4% power conversion efficiency (~ 11.5% in the cell effective area) CZTSSe cell with improved Voc of up to 90 mV has been attained. This demonstration may provide a new direction of further boosting the performance of copper chalcogenide based solar cells as well.

Surface morphological, structural, electrical and optical properties of GaN-based light-emitting diodes using submicron-scaled Ag islands and ITO thin films

An ITO-Ag islands complex as a new transparent conducting electrode (TCE) structure (on the 5 nm-thick p-InGaN/90 nm-thick p-GaN) for achieving high-performance and more reliable GaN-based LEDs were fabricated. A normal LED with a conventional ITO TCE was also compared. The surface morphological, structural, electrical and optical properties of fabricated GaN-based light-emitting diodes using a complex electrode of submicron-scaled Ag islands and ITO thin films are explored by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), current-voltage (I-V) and output power-current (L-I) techniques. Surface morphology investigations revealed Ag islands formed uniformly on the p-InGaN/p-GaN surface during rapid thermal annealing at 400 °C for 1 min in N2 ambient. The ohmic properties and overall device-performance of the suggested contact and device structures were superior to those in the conventional ITO contact and normal ITO LED structures. Based on the results of XRD and XPS measurements, the formation of the intermetallic gallide phases (AgGa) is responsible for better performance characteristics of the ITO-Ag islands device. The significant improvements are described in terms of the conducting bridge influence, highly effective micro-mirror effect, and wider photon window via the roughened structure.

Specific contact resistance of IGZO thin film transistors with metallic and transparent conductive oxides electrodes and XPS study of the contact/semiconductor interfaces

In this work, the specific contact resistance (ρc) between amorphous indium-gallium-zinc-oxide (IGZO) semiconductor and different contact electrodes was obtained from thin film transistors (TFTs). Ti/Au (10/100 nm), aluminum doped zinc oxide (AZO, 100 nm) and indium tin oxide (ITO, 100 nm) were used as source/drain electrodes to fabricate IGZO TFTs. Chemical states of the contacts/semiconductor interfaces were examined by depth profile X-ray photoelectron spectroscopy (XPS) analysis to explain the origin of the differences on specific contact resistance. The lowest ρc achieved using Ti/Au was related to the formation of a TiOx interlayer due to oxygen atoms diffusing out from the semiconductor under layer, increasing the carrier concentration of IGZO at the interface and lowering the ρc. On the contrary, no interfacial reactions were observed between IGZO and AZO or ITO source/drain. However, IGZO resistivity increased with ITO contacts likely due to oxygen vacancies filling during ITO deposition. This fact seems to be the origin of the high contact resistance between IGZO and ITO, compared to IGZO-AZO and IGZO-Ti/Au interfaces.