SnOx Films Research Articles

Impact of Tetrakis(dimethylamido)tin(IV) Degradation on Atomic Layer Deposition of Tin Oxide Films and Perovskite Solar Cells.

Tin oxide (SnOx) films synthesized by atomic layer deposition (ALD) are widely explored in a range of optoelectronic devices including electrochemical sensors, transistors, and photovoltaics. However, the integrity of the key ALD-SnOx precursor, namely tetrakis(dimethylamido)tin (IV) (TDMASn), and its influence on the properties of ultimate films remain unexplored. Here a significant degradation of TDMASn into bis(dimethylamido)tin(II) via the Sn-imine complex is reported, and its impact on the corresponding films and devices is examined. It is found, surprisingly, that this degradation does not affect the growth kinetics and morphology of ALD-SnOx films. But it notably deteriorates their electronic properties, resulting in films with twice the electrical resistance due to different oxidation mechanisms of the degradation products. Perovskite solar cells employing such films exhibit a significant loss in power conversion efficiency, primarily due to charge transport and transfer losses. These findings urge strategies to stabilize TDMASn, a critical precursor for ALD-SnOx films, or to identify alternative materials to achieve efficient and reliable devices.

Low‐Cost Tin Oxide Transparent Conductive Films for Silicon Heterojunction Solar Cells

AbstractIndium‐based transparent conductive oxide (TCO) films are widely used in various photoelectric devices including silicon heterojunction (SHJ) solar cells. However, high cost of indium‐based TCO films is not conducive to mass production of the SHJ solar cells. A variety of indium‐free or indium‐less TCOs are explored and utilized presently. Here, SnOx films are deposited by reactive plasma deposition (RPD) with metal tin as the evaporation source. The metal‐reaction deposited SnOx films feature low resistivity (<2 × 10−3 Ω cm), high mobility (35.93 cm2 V−1 S−1), and wide optical bandgap (3.64 eV). A power conversion efficiency (PCE) of 25.33% is achieved on the champion SHJ solar cell using the metal‐reaction deposited SnOx as the back TCO layer, which indicates the application potential of the metal‐reaction‐deposited SnOx as a low‐cost substitute for In‐based TCOs in SHJ solar cells and other photoelectric devices.

Investigation of diodic behavior in p-NiO/n-SnO2 bilayer heterojunctions fabricated via DC magnetron reactive sputtering

Tin oxide (SnOx) thin films at varying oxygen flow rates and Nickel oxide (NiO) thin films were deposited by reactive dc magnetron sputtering on glass substrates. Structural, chemical, morphological, optical and electrical properties of the deposited films were studied. XRD studies confirmed that the deposited films were polycrystalline in nature. SnOx thin films have shown two phases such as SnO and SnO2. AFM and SEM were used to analyse the morphology of the films and EDS confirmed the presence of Sn and Ni in the respective films. The examination of the x-ray photoelectron spectrum showed that the sputtered SnOx films contain both Sn2+ and Sn4+ oxidation states and NiO films contain Ni+2 and Ni+3 oxidation states. Photoluminescence study shows strong violet and weak red emission peaks for SnOx films and NiO showed strong emission peaks in the orange-red region. The optical results demonstrate that the films were transparent. The bandgap of SnOx and NiO samples were ∼3.3 eV and − 3.42 eV, respectively. Further we constructed a p-NiO/n-SnO2 heterojunction diode and its electrical characteristics were thoroughly assessed. Using dark current–voltage measurements, electrical characteristics such saturation current, ideality factor and barrier height were determined. The increase in oxygen flow rate led to reduction in the rectification of the devices. Our findings support the creation of high-performance metal oxide heterojunction for optoelectronic devices.

Compliance-free, analog RRAM devices based on SnOx

Brain-inspired resistive random-access memory (RRAM) technology is anticipated to outperform conventional flash memory technology due to its performance, high aerial density, low power consumption, and cost. For RRAM devices, metal oxides are exceedingly investigated as resistive switching (RS) materials. Among different oxides, tin oxide (SnOx) received minimal attention, although it possesses excellent electronic properties. Herein, we demonstrate compliance-free, analog resistive switching behavior with several stable states in Ti/Pt/SnOx/Pt RRAM devices. The compliance-free nature might be due to the high internal resistance of SnOx films. The resistance of the films was modulated by varying Ar/O2 ratio during the sputtering process. The I–V characteristics revealed a well-expressed high resistance state (HRS) and low resistance states (LRS) with bipolar memristive switching mechanism. By varying the pulse amplitude and width, different resistance states have been achieved, indicating the analog switching characteristics of the device. Furthermore, the devices show excellent retention for eleven states over 1000 s with an endurance of > 100 cycles.

Tunable properties of SnOx sputter-deposited by RGPP and GLAD techniques: A potential candidate for photosensing and all-oxide solar cells

In this work, optical and electrical properties of tin-oxide (SnOx) thin-films were investigated for broadband photosensing and photovoltaic applications. The GLancing Angle Deposition (GLAD) and Reactive Gas Pulsing Process (RGPP) techniques were used to study the effects of the oxygen ratio variation and deposition angle on the film optoelectronic and photovoltaic properties. The deposition angle of the particle flux was kept at 80° and the injected oxygen gas concentration was tuned by changing the oxygen pulsing time from 0 to 20 s. It is found that the material band gap increases from 0.9 eV to 3.56 eV when the oxygen content increases. The deposited SnOx films exhibited improved and tuned optoelectronic properties, demonstrating their potential applications for developing alternative broadband photosensing layers and eco-friendly all-oxide solar cells. In this regard, SnOx-based photosensor and all-oxide SnOx solar cell structures were developed using the deposited thin-films. It is revealed that the prepared SnOx photosensor shows the highest responsivity of 32.7 mA/W and improved ION/IOFF ratio of 48 dB. Moreover, the optimized all-oxide SnOx solar cell demonstrates a high efficiency of 3.41 %, a short-circuit current of 14.53 mA/cm2 and an open circuit voltage of 0.49 V. These interesting results make the proposed elaboration process based on combined RGPP and GLAD techniques highly suitable for the development of high-performance optoelectronic and photovoltaic devices based on cost-effective metal oxide materials.

Constructing tin oxides Interfacial Layer with Gradient Compositions for Efficient Perovskite/Silicon Tandem Solar Cells with Efficiency Exceeding 28.

Atomic layer deposition (ALD) growth of conformal thin SnOx films on perovskite absorbers offers a promising method to improve carrier-selective contacts, enable sputter processing, and prevent humidity ingress toward high-performance tandem perovskite solar cells. However, the interaction between perovskite materials and reactive ALD precursor limits the process parameters of ALD-SnOx film and requires an additional fullerene layer. Here, it demonstrates that reducing the water dose to deposit SnOx can reduce the degradation effect upon the perovskite underlayer while increasing the water dose to promote the oxidization can improve the electrical properties. Accordingly, a SnOx buffer layer with a gradient composition structure is designed, in which the compositionally varying are achieved by gradually increasing the oxygen source during the vapor deposition from the bottom to the top layer. In addition, the gradient SnOx structure with favorable energy funnels significantly enhances carrier extraction, further minimizing its dependence on the fullerene layer. Its broad applicability for different perovskite compositions and various textured morphology is demonstrated. Notably, the design boosts the efficiencies of perovskite/silicon tandem cells (1.0cm2) on industrially textured Czochralski (CZ) silicon to a certified efficiency of 28.0%.

Promising SnOx electron transport layer for polymer solar cells

In this study, SnOx films were synthesized via thermal oxidation of Sn films at various temperatures ranging from 300 °C to 500 °C. The impact of oxidation temperature on the structural, optical, and electronic properties of the SnOx films was investigated using SEM, EDX, optical absorption, and impedance spectroscopy techniques. It was found that the oxidation temperature has a significant impact on the SnOx resistance, which decreases as the temperature increases due to improved SnOx crystallinity and enhanced electron mobility. Furthermore, an increase in recombination resistance suggests an improvement in interface quality and reduced charge recombination processes. Finally, the impact of SnOx electron transport layer properties on the photovoltaic characteristics of organic solar cells was investigated. It was observed that OSCs based on SnOx ETL obtained at higher oxidation temperature reveal enhanced photovoltaic characteristics.

The effect of electrolyte temperature on the growth, morphology, and properties of porous anodic tin oxide films

The effect of electrolyte temperature on the anodic formation of nanoporous tin oxide layers, their morphology and properties was studied in detail. Electrochemical synthesis of SnOx films was carried out in both acidic (H2C2O4) and alkaline (NaOH) electrolytes at various potentials. Differences in morphological features of as-generated films and the kinetics of their formation were carefully investigated from FE-SEM images. The effect of anodizing temperature was successfully verified revealing its undeniable importance when designing the anodization procedure. For instance, both in acidic and alkaline electrolytes, applying too low temperatures results in formation of cracked oxide layers with the least open pores or compact surface, while too high temperatures (≥40 °C) leads to obtaining films with clogged pores due to the partial etching of the material by the electrolyte. Anodizing temperature was also found to be a crucial parameter responsible for the type of morphology of the synthesized materials (compact or porous layers or even crater-like hierarchical structures) when the process is carried out at higher potentials (here 9 V). Finally, we have proved that the impact of electrolyte temperature on the crystallinity of the anodic tin oxide layers is negligible, whereas the photoelectrochemical activity is significantly influenced due to the tight relation with the morphology of as-synthesized materials.

Room-Temperature Fabrication of p-Type SnO Semiconductors Using Ion-Beam-Assisted Deposition.

Over the past decade, SnO has been considered a promising p-type oxide semiconductor. However, achieving high mobility in the fabrication of p-type SnO films is still highly dependent on the post-annealing procedure, which is often used to make SnO, due to its metastable nature, readily convertible to SnO2 and/or intermediate phases. This paper demonstrates a fully room-temperature fabrication of p-type SnOx thin films using ion-beam-assisted deposition. This technique offers independent control between ion density, via the ion-gun anode current and oxygen flow rate, and ion energy, via the ion-gun anode voltage, thus being able to optimize the optical band gap and the hole mobility of the SnO films to reach 2.70 eV and 7.89 cm2 V-1 s-1, respectively, without the need for annealing. Remarkably, this is the highest mobility reported for p-type SnO films whose fabrication was carried out entirely at room temperature. Using first-principles calculations, we rationalize that the high mobility is associated with the fine-tuning of the Sn-rich-related defects and lattice densification, obtained by controlling the density and energy of the oxygen ions, both of which optimize the spatial overlap of the valence bands to form a continuous conduction path for the holes. Moreover, due to the absence of the annealing process, the Raman spectra reveal no significant signatures of microcrystal formation in the films. This behavior contrasts with the case involving the air-annealing procedure, where a complex interaction occurs between the formation of SnO microcrystals and the formation of SnOx intermediate phases. This interplay results in variations in grain texture within the film, leading to a lower optimum Hall mobility of only 5.17 cm2 V-1 s-1. Finally, we demonstrate the rectification characteristics of all-fabricated-at-room-temperature SnOx-based p-n devices to confirm the viability of the p-type SnOx films.

Study of wide bandgap SnOx thin films grown by a reactive magnetron sputtering via a two-step method

In the present work, we report on the microstructural and optoelectronic properties of SnOx thin films deposited by a reactive radio frequency magnetron sputtering. After SnOx growth by sputtering under O2/Ar flow, we have used three different treatment methods, namely (1) as deposited films under O2/Ar, (2) vacuum annealed films ex-situ, and (3) air annealed films ex-situ. Effects of the O2/Ar ratios and the growth temperature were investigated for each treatment method. We have thoroughly investigated the structural, optical, electrical and morphology of the different films by several advanced techniques. The best compromise between electrical conductivity and optical transmission for the use of these SnOx films as an n-type TCO was the conditions O2/Ar = 1.5% during the growth process, at 250 °C, followed by a vacuum post thermal annealing performed at 5 × 10–4 Torr. Our results pointed out clear correlations between the growth conditions, the microstructural and optoelectronic properties, where highly electrically conductive films were found to be associated to larger grains size microstructure. Effects of O2/Ar flow and the thermal annealing process were also analysed and discussed thoroughly.

Deposition Mechanism and Characterization of Plasma-Enhanced Atomic Layer-Deposited SnOx Films at Different Substrate Temperatures.

The promising functional tin oxide (SnOx) has attracted tremendous attention due to its transparent and conductive properties. The stoichiometric composition of SnOx can be described as common n-type SnO2 and p-type Sn3O4. In this study, the functional SnOx films were prepared successfully by plasma-enhanced atomic layer deposition (PEALD) at different substrate temperatures from 100 to 400 °C. The experimental results involving optical, structural, chemical, and electrical properties and morphologies are discussed. The SnO2 and oxygen-deficient Sn3O4 phases coexisting in PEALD SnOx films were found. The PEALD SnOx films are composed of intrinsic oxygen vacancies with O-Sn4+ bonds and then transformed into a crystalline SnO2 phase with increased substrate temperature, revealing a direct 3.5–4.0 eV band gap and 1.9–2.1 refractive index. Lower (<150 °C) and higher (>300 °C) substrate temperatures can cause precursor condensation and desorption, respectively, resulting in reduced film qualities. The proper composition ratio of O to Sn in PEALD SnOx films near an estimated 1.74 suggests the highest mobility of 12.89 cm2 V−1 s−1 at 300 °C.

Improving the photoelectrochemical performance of porous anodic SnO x films by adjusting electrosynthesis conditions

A comprehensive characterization of photoelectrochemical (PEC) properties of the nanoporous tin oxide (SnOx) films of different thicknesses and complex internal morphology is presented. Nanoporous SnOx layers were obtained by one-step anodic oxidation (anodization) of Sn foil in 1 M NaOH. Semiconducting films with a uniform diameter of ca. 50 nm were grown if the potential of 4 V was applied during anodization, and the layers with different thicknesses were synthesized by changing the duration of the process. Switching the potential between 2 and 4 V allows the formation of anodic films with segments of different channel diameters. The optimal anodizing duration for layers with uniform channels was found to be 50 minutes, which corresponds to the thickness of SnOx film of slightly above 6 μm. In the case of layers with segments of different channel diameters, the segment arrangement was found to be crucial for optimal PEC performance. Layers with the segment of narrower channels being in the contact with the current collector were found to exhibit enhanced photoelectrochemical performance compared to their counterparts with an opposite segment arrangement. This was mainly attributed to the favorable band arrangement facilitating the transfer of the photogenerated electrons to the external circuit as well as enhanced adhesion of the anodic SnOx layer to the current collector. Highlights Nanoporous SnOx films were synthesized electrochemically. Layers with various morphologies were studied as photoanodes. The optimal thickness of anodic SnOx was found to be 6 μm. Enhanced PEC performance was observed for multisegment anodic films. The segment arrangement is crucial for optimal PEC performance.

Normally-off Hydrogen-Terminated Diamond Field-Effect Transistor with SnOx Dielectric Layer Formed by Thermal Oxidation of Sn

SnOx films were deposited on a hydrogen-terminated diamond by thermal oxidation of Sn. The X-ray photoelectron spectroscopy result implies partial oxidation of Sn film on the diamond surface. The leakage current and capacitance–voltage properties of Al/SnOx/H-diamond metal-oxide-semiconductor diodes were investigated. The maximum leakage current density value at −8.0 V is 1.6 × 10−4 A/cm2, and the maximum capacitance value is measured to be 0.207 μF/cm2. According to the C–V results, trapped charge density and fixed charge density are determined to be 2.39 × 1012 and 4.5 × 1011 cm−2, respectively. Finally, an enhancement-mode H-diamond field effect transistor was obtained with a VTH of −0.5 V. Its IDMAX is −21.9 mA/mm when VGS is −5, VDS is −10 V. The effective mobility and transconductance are 92.5 cm2V−1 s−1 and 5.6 mS/mm, respectively. We suspect that the normally-off characteristic is caused by unoxidized Sn, whose outermost electron could deplete the hole in the channel.

CdS-Decorated Porous Anodic SnOx Photoanodes with Enhanced Performance under Visible Light

Electrochemically generated nanoporous tin oxide films have already been studied as photoanodes in photoelectrochemical water splitting systems. However, up to now, the most significant drawback of such materials was their relatively wide band gap (ca. 3.0 eV), which limits their effective performance in the UV light range. Therefore, here, we present for the first time an effective strategy for sensitization of porous anodic SnOx films with another narrow band gap semiconductor. Nanoporous tin oxide layers were obtained by simple one-step anodic oxidation of metallic Sn in 1 M NaOH followed by further surface decoration with CdS by the successive ionic layer adsorption and reaction (SILAR) method. It was found that the nanoporous morphology of as-anodized SnOx is still preserved after CdS deposition. Such SnOx/CdS photoanodes exhibited enhanced photoelectrochemical activity in the visible range compared to unmodified SnOx. However, the thermal treatment at 200 °C before the SILAR process was found to be a key factor responsible for the optimal photoresponse of the material.

Effect of sodium doping on characteristics of p-SnOx films prepared by reactive direct current magnetron sputtering

Conventionally, p-type semiconducting oxide films of high optical transmission and good electric conduction are materials of great demand in electronic and optoelectric devices. They can conveniently be integrated with their n-type counterparts for formation of homo or heterojunctions. In this report, Na-doped SnOx films were fabricated by reactively sputtering the Sn + Na alloy targets at substrate temperature of 200 °C. Effect of Na dopant concentration on crystal structure, electric and optical properties of Na-doped SnOx films was investigated with X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, Hall and UV–Visible transmission spectroscopy. The obtained results revealed that when Na + substituted Sn2+, the hole concentration increased but the crystallite size reduced, leading to increased grain boundary and reduced carrier mobility. However, electric resistivity still reduced thanks to the increase of carrier concentration. Averange optical transmission of Na-doped SnOx films in visible range was approximately 65%. In addition, optical bandgap value reduced as Na doping amount in those films increased. The Na-doped SnOx films sputtered from Sn + 3 at% Na alloy targets, corresponding to 1.56 at% Na existing in films, presented the best electric property (nH = 2.75 × 1019cm−3, μ = 2.4 cm2/VS, ρ = 9.35 × 10−2Ωcm). This film proceeded with diode structure of glass/FTO/n-nc-Si:H/p-SnOx:Na/Cu, resulted in the best characteristics (VOC = 0.59 V, n = 3.57, rectifying ratio = 22, Rs = 38.1 Ω).

Soft X-ray absorption study of sputtered tin oxide films

The bonding structure of tin oxide (SnOx) films grown by reactive DC magnetron sputtering has been studied by the combination of X-ray diffraction (XRD) and soft X-ray absorption near-edge structure (XANES). The oxygen incorporation in the films has been controlled by the O2 partial pressure (PO2) in the O2/Ar discharge mixture. In addition, the impact of substrate heating and post-deposition flash lamp annealing (FLA) on crystal growth has been studied. In general, it has been stablished a transition from SnO to SnO2 arrangements by increasing PO2, where XRD and XANES provide complementary results about the formation of single- and mixed-phase films. In samples produced at room temperature, XANES gives unique information about such structural evolution, as well as related to defects like the incorporation of O2 molecules at high PO2. FLA on samples grown at room temperature promotes crystal growth and the phase evolution follows the initial structural selectivity. Finally, the optical properties and surface morphology of the films have been correlated with the structural identification.

Study on the Crystallinity and Oxidation States of Nanoporous Anodized Tin Oxide Films Regulated by Annealing Treatment for Supercapacitor Application

In this study, electrodeposition combined with anodization was employed to prepare a nanoporous tin oxide film on a pure copper substrate. It was found that annealing temperature played a critically significant role in regulating the crystallinity, pore size, and contents of different oxidation states of the anodized tin oxide film to affect the electrochemical performance. The study verified that SnOx films treated by optimized annealing at 500 °C with precisely controlling the nanoporous morphology and crystallinity displayed competitive specific capacitance at an appropriate ratio of Sn4+ to Sn2+. A maximum specific capacitance of 86.2 mF/cm2 could be achieved at this temperature, and the capacitance retention rate still exceeded 90% even after 8000 charge-discharge cycles. With properly designed annealing treatment, we implemented tin film anodization to obtain an optimized electrode with significantly enhanced electrochemical performance, which shows a promising application in the electrochemical field to prepare electrodes.

Reaction mode-controlled crystal structure and optical and electrical properties of SnOx infrared transparent conducting films

In this study, the reaction mode of high-power pulsed reactive magnetron sputtering and the crystal structure and infrared transparent conductive properties of SnOx thin films prepared at 600 °C were investigated. The effects of sputtering at different oxygen partial pressures from 10 to 24 sccm were examined. For SnOx films deposited at oxygen partial pressures of 10–14 sccm, the reaction mode was dominated by the metallic mode, and the polar unsaturated (101) plane was the preferred orientation of the film crystals. For SnOx films deposited at oxygen partial pressures of 16–18 sccm, the reaction mode was dominated by the transition mode, showing a preferred (110) plane orientation. In the deposition process, at oxygen partial pressure >18 sccm, the reaction proceeded in poisoning mode. As the oxygen partial pressure was increased, the carrier concentration decreased to 1.140 × 1015 cm−3, mobility increased to 14.93 cm2/Vs, and IR transmittance at 4 μm increased. Furthermore, excess O2 resulted in deteriorated electrical properties of the prepared SnOx films, with a maximum resistivity of 502.9 Ω·cm.

Atomic-Layer-Deposited SiOx/SnOx Nanolaminate Structure for Moisture and Hydrogen Gas Diffusion Barriers.

High-density SnOx and SiOx thin films were deposited via atomic layer deposition (ALD) at low temperatures (100 °C) using tetrakis(dimethylamino)tin(IV) (TDMASn) and di-isopropylaminosilane (DIPAS) as precursors and hydrogen peroxide (H2O2) and O2 plasma as reactants, respectively. The thin-film encapsulation (TFE) properties of SnOx and SiOx were demonstrated with thickness dependence measurements of the water vapor transmission rate (WVTR) evaluated at 50 °C and 90% relative humidity, and different TFE performance tendencies were observed between thermal and plasma ALD SnOx. The film density, crystallinity, and pinholes formed in the SnOx film appeared to be closely related to the diffusion barrier properties of the film. Based on the above results, a nanolaminate (NL) structure consisting of SiOx and SnOx deposited using plasma-enhanced ALD was measured using WVTR (H2O molecule diffusion) at 2.43 × 10-5 g/m2 day with a 10/10 nm NL structure and time-lag gas permeation measurement (H2 gas diffusion) for applications as passivation layers in various electronic devices.

All-Oxide p-n Junction Thermoelectric Generator Based on SnOx and ZnO Thin Films.

Achieving thermoelectric devices with high performance based on low-cost and nontoxic materials is extremely challenging. Moreover, as we move toward an Internet-of-Things society, a miniaturized local power source such as a thermoelectric generator (TEG) is desired to power increasing numbers of wireless sensors. Therefore, in this work, an all-oxide p-n junction TEG composed of low-cost, abundant, and nontoxic materials, such as n-type ZnO and p-type SnOx thin films, deposited on borosilicate glass substrate is proposed. A type II heterojunction between SnOx and ZnO films was predicted by density functional theory (DFT) calculations and confirmed experimentally by X-ray photoelectron spectroscopy (XPS). Moreover, scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray spectroscopy (EDS) show a sharp interface between the SnOx and ZnO layers, confirming the high quality of the p-n junction even after annealing at 523 K. ZnO and SnOx thin films exhibit Seebeck coefficients (α) of ∼121 and ∼258 μV/K, respectively, at 298 K, resulting in power factors (PF) of 180 μW/m K2 (for ZnO) and 37 μW/m K2 (for SnOx). Moreover, the thermal conductivities of ZnO and SnOx films are 8.7 and 1.24 W/m K, respectively, at 298 K, with no significant changes until 575 K. The four pairs all-oxide TEG generated a maximum power output (Pout) of 1.8 nW (≈126 μW/cm2) at a temperature difference of 160 K. The output voltage (Vout) and output current (Iout) at the maximum power output of the TEG are 124 mV and 0.0146 μA, respectively. This work paves the way for achieving a high-performance TEG device based on oxide thin films.