ILGAR In2S3 buffer layers for Cd‐free Cu(In,Ga)(S,Se)2 solar cells with certified efficiencies above 16%

In₂S₃ buffer layers have been prepared using the spray ion layer gas reaction deposition technique for chalcopyrite‐based thin‐film solar cells. These buffers deposited on commercially available Cu(In,Ga)(S,Se)₂ absorbers have resulted in solar cells with certified record efficiencies of 16.1%, clearly higher than the corresponding CdS‐buffered references. The deposition process has been optimized, and the resulting cells have been studied using current–voltage and quantum efficiency analysis and compared with previous record cells, cells with a thermally evaporated In₂S₃ buffer layer and CdS references. Copyright © 2012 John Wiley & Sons, Ltd.     

Buffer and anode-integrated WO3-doped In2O3 electrodes for PEDOT:PSS-free organic photovoltaics

We developed PEDOT:PSS-free organic solar cells (OSCs) using WO₃ and In₂O₃ (IWO) mixed electrodes acting as a buffer hole injection layer (HIL) and anode simultaneously. Through the co-sputtering and rapid thermal annealing (RTA) of WO₃ and In₂O₃, we achieved buffer and anode-integrated transparent electrodes with a sheet resistance of 17 Ohm/square, a transmittance of 90.32%, and a work function of 4.83 eV, all of which are comparable to values obtained with a conventional ITO anode. Due to the existence of WO₃ in the In₂O₃ matrix, OSCs fabricated on an IWO electrode with no acidic PEDOT:PSS buffer layer showed a PCE of 2.87%. Therefore, a transparent IWO electrode simultaneously acting as an HIL and anode layer can be considered a promising transparent electrode for cost-efficient and reliable OSCs because it could eliminate the use of acidic PEDOT:PSS buffer layer.     

Surface photovoltage spectroscopy on Cu(In,Ga)(S,Se)2/ZnS‐nanodot/In2S3 systems

Single layers and combined layer systems with Cu(In,Ga)(S,Se)₂, ZnS‐nanodot (nd) and In₂S₃ layers were investigated by surface photovoltage spectroscopy in the Kelvin‐probe arrangement and compared with the open‐circuit voltage (V_OC) of solar cells. The In₂S₃ and ZnS‐nd layers were prepared by the spray ion layer gas reaction (ILGAR) technique from Indium chloride (InCl₃), Indium acetylacetonate (In(acac)₃) and Zinc acetylacetonate, respectively. The surface photovoltage signals of Cu(In,Ga)(S,Se)₂ were larger for the Cu(In,Ga)(S,Se)₂/ZnS‐nd/In₂S₃ than for the Cu(In,Ga)(S,Se)₂/In₂S₃ layer system showing that a ZnS‐nd layer additionally passivated the Cu(In,Ga)(S,Se)₂ surface. ILGAR In₂S₃ deposition from InCl₃ precursor solution led to a modification of surface defects of ZnS‐nd and to generation of defect states below the band gap of Cu(In,Ga)(S,Se)₂, which has not been observed for deposition from Indium acetylacetonate precursor. Defect generation during ILGAR In₂S₃ deposition with InCl₃ precursor resulted in a lower V_OC of Cu(In,Ga)(S,Se)₂/ZnS‐nd/In₂S₃/ZnO : Al solar cells. Copyright © 2012 John Wiley & Sons, Ltd.     

Study on ALD In2S3/Cu(In,Ga)Se2 interface formation

The formation of the interface between In₂S₃ grown by atomic layer deposition (ALD) and co‐evaporated Cu(In,Ga)Se₂ (CIGS) has been studied by X‐ray and UV photoelectron spectroscopy. The valence band offset at 160°C ALD substrate temperature was determined as −1·2±0·2 eV for CIGS deposited on soda‐lime glass substrates and −1·4±0·2 eV when a Na barrier substrate was used. Wavelength dependent complex refractive index of In₂S₃ grown directly on glass was determined from inversion of reflectance and transmittance spectra. From these data, an indirect optical bandgap of 2·08±0·05 eV was deduced, independent of film thickness, of substrate temperature and of Na content. CIGS solar cells with ALD In₂S₃ buffer layers were fabricated. Highest device efficiency of 12·1% was obtained at a substrate temperature of 120°C. Using the bandgap obtained for In₂S₃ on glass and a 1·15±0·05 eV bandgap determined for the bulk of the CIGS absorber, the conduction band offset at the buffer interface was estimated as −0·25±0·2 eV (−0·45±0·2 eV) for Na‐containing (Na‐free) CIGS. Copyright © 2005 John Wiley & Sons, Ltd.     

Oriented Growth of Al2O3:ZnO Nanolaminates for Use as Electron‐Selective Electrodes in Inverted Polymer Solar Cells

Atomic layer deposition is used to synthesize Al₂O₃:ZnO(1:x) nanolaminates with the number of deposition cycles, x, ranging from 5 to 30 for evaluation as optically transparent, electron‐selective electrodes in polymer‐based inverted solar cells. Al₂O₃:ZnO(1:20) nanolaminates are found to exhibit the highest values of electrical conductivity (1.2 × 10³ S cm^?1; more than six times higher than for neat ZnO films), while retaining a high optical transmittance (≥80% in the visible region) and a low work function (4.0 eV). Such attractive performance is attributed to the structure (ZnO crystal size and crystal alignment) and doping level of this intermediate Al₂O₃:ZnO film composition. Polymer‐based inverted solar cells using poly(3‐hexylthiophene) (P3HT):phenyl‐C₆₁‐butyric acid methyl ester (PCBM) mixtures in the active layer and Al₂O₃:ZnO(1:20) nanolaminates as transparent electron‐selective electrodes exhibit a power conversion efficiency of 3% under simulated AM 1.5 G, 100 mW cm^?2 illumination.     

Growth kinetics,properties, performance,and stability of atomic layer deposition Zn–Sn–O buffer layers for Cu(In,Ga)Se2 solar cells

A new atomic layer deposition process was developed for deposition of Zn–Sn–O buffer layers for Cu(In,Ga)Se₂ solar cells with tetrakis(dimethylamino) tin, Sn(N(CH₃)₂)₄, diethyl zinc, Zn(C₂H₅)₂, and water, H₂O. The new process gives good control of thickness and [Sn]/([Sn] + [Zn]) content of the films. The Zn–Sn–O films are amorphous as found by grazing incidence X‐ray diffraction, have a high resistivity, show a lower density compared with ZnO and SnO_x, and have a transmittance loss that is smeared out over a wide wavelength interval. Good solar cell performance was achieved for a [Sn]/([Sn] + [Zn]) content determined to be 0.15–0.21 by Rutherford backscattering. The champion solar cell with a Zn–Sn–O buffer layer had an efficiency of 15.3% (V_oc = 653 mV, J_sc(QE) = 31.8 mA/cm², and FF = 73.8%) compared with 15.1% (V_oc = 663 mV, J_sc(QE) = 30.1 mA/cm², and FF = 75.8%) of the best reference solar cell with a CdS buffer layer. There is a strong light‐soaking effect that saturates after a few minutes for solar cells with Zn–Sn–O buffer layers after storage in the dark. Stability was tested by 1000 h of dry heat storage in darkness at 85 °C, where Zn–Sn–O buffer layers with a thickness of 76 nm retained their initial value after a few minutes of light soaking. Copyright © 2011 John Wiley & Sons, Ltd.     

Exploring the Leidenfrost Effect for the Deposition of High‐Quality In2O3 Layers via Spray Pyrolysis at Low Temperatures and Their Application in High Electron Mobility Transistors

The growth mechanism of indium oxide (In₂O₃) layers processed via spray pyrolysis of an aqueous precursor solution in the temperature range of 100–300 °C and the impact on their electron transporting properties are studied. Analysis of the droplet impingement sites on the substrate's surface as a function of its temperature reveals that Leidenfrost effect dominated boiling plays a crucial role in the growth of smooth, continuous, and highly crystalline In₂O₃ layers via a vapor phase‐like process. By careful optimization of the precursor formulation, deposition conditions, and choice of substrate, this effect is exploited and ultrathin and exceptionally smooth layers of In₂O₃ are grown over large area substrates at temperatures as low as 252 °C. Thin‐film transistors (TFTs) fabricated using these optimized In₂O₃ layers exhibit superior electron transport characteristics with the electron mobility reaching up to 40 cm² V^?1 s^?1, a value amongst the highest reported to date for solution‐processed In₂O₃ TFTs. The present work contributes enormously to the basic understanding of spray pyrolysis and highlights its tremendous potential for large‐volume manufacturing of high‐performance metal oxide thin‐film transistor electronics.     

Aluminum‐doped Zn1 − xMgxO as transparent conductive oxide of Cu(In,Ga)(S,Se)2‐based solar cell for minimizing surface carrier recombination

A 19.5%‐efficient Cu(In,Ga)(S,Se)₂ (CIGSSe)‐based solar cell is obtained by replacing traditional CdS/ZnO buffer layers with Cd_0.75Zn_0.25S/Zn_0.79Mg_0.21O buffer layers for increasing short‐circuit current density because band‐gap energies of Cd_0.75Zn_0.25S and Zn_0.79Mg_0.21O are wider than those of CdS and ZnO, respectively. This yields the increase in external quantum efficiency in a short wavelength range of approximately 320 to 550 nm. Moreover, difference of conduction band minimum (E _C) between Zn_1 − x Mg_x O:Al (transparent conductive oxide, TCO) layer and CIGSSe absorber is optimized by varying [Mg]/([Mg] + [Zn]), x . It is revealed that Zn_1 − x Mg_x O:Al films with [Mg]/([Mg] + [Zn]) in a range of 0.10 to 0.12, enhancing E _g from 3.72 to 3.76 eV, are appropriate as TCO because of their enhanced mobility and decreased carrier density. Addition of 12% Mg into ZnO:Al to form Zn_0.88Mg_0.12O:Al as TCO layer effectively decreases surface carrier recombination and improves photovoltaic parameters, especially open‐circuit voltage and fill factor. This is the first experimental proof of the concept for optimizing E _C difference between TCO and absorber to minimize surface carrier recombination. Ultimately, conversion efficiency (η ) of CIGSSe solar cell with alternative Cd_0.75Zn_0.25S/Zn_0.79Mg_0.21O/Zn_0.88Mg_0.12O:Al (TCO) layers is enhanced to 20.6%, owing to control of total E _C alignment, which is higher η up to 12.6% relative as compared with the solar cell with traditional CdS/ZnO/ZnO:Al layers.     

The effect of Zn1−xSnxOy buffer layer thickness in 18.0% efficient Cd‐free Cu(In,Ga)Se2 solar cells

The influence of the thickness of atomic layer deposited Zn_1−xSn_xO_y buffer layers and the presence of an intrinsic ZnO layer on the performance of Cu(In,Ga)Se₂ solar cells are investigated. The amorphous Zn_1−xSn_xO_y layer, with a [Sn]/([Sn] + [Zn]) composition of approximately 0.18, forms a conformal and in‐depth uniform layer with an optical band gap of 3.3 eV. The short circuit current for cells with a Zn_1−xSn_xO_y layer are found to be higher than the short circuit current for CdS buffer reference cells and thickness independent. On the contrary, both the open circuit voltage and the fill factor values obtained are lower than the references and are thickness dependent. A high conversion efficiency of 18.0%, which is comparable with CdS references, is attained for a cell with a Zn_1−xSn_xO_y layer thickness of approximately 13 nm and with an i‐ZnO layer. Copyright © 2012 John Wiley & Sons, Ltd.     

Metastable Hexagonal In2O3 Nanofibers Templated from InOOH Nanofibers under Ambient Pressure

Single‐crystal, metastable, hexagonal In₂O₃ (H‐In₂O₃) nanofibers with an average diameter of 80 nm and length of up to several micrometers were synthesized on a large scale, for the first time under ambient pressure, by annealing InOOH nanofibers at 490 °C. The InOOH nanofibers were prepared by a controlled hydrolysis solvothermal reaction, using InCl₃·4H₂O as the starting material and ether as the solvent, in the temperature range of 190–240 °C. The solvent has significant effects on the formation of the metastable phase and the morphology of the In₂O₃ nanocrystals during the synthesis of the precursor InOOH. Room‐temperature optical absorption spectra of the hexagonal In₂O₃ nanofibers showed strong absorption peak located at 325 nm (3.83 eV) with a slight blue‐shift compared with that of bulk In₂O₃ (3.75 eV). The H‐In₂O₃ nanofibers photoluminesce at room temperature with emission peaks at 378 nm, 398 nm, and 420 nm. The successful production of metastable hexagonal In₂O₃ nanofibers in large scale under mild conditions could be of interest both for applications and fundamental studies.     

The Remarkable Thermal Stability of Amorphous In‐Zn‐O Transparent Conductors

Transparent conducting oxides (TCOs) are increasingly critical components in photovoltaic cells, low‐e windows, flat panel displays, electrochromic devices, and flexible electronics. The conventional TCOs, such as Sn‐doped In₂O₃, are crystalline single phase materials. Here, we report on In‐Zn‐O (IZO), a compositionally tunable amorphous TCO with some significantly improved properties. Compositionally graded thin film samples were deposited by co‐sputtering from separate In₂O₃ and ZnO targets onto glass substrates at 100 °C. For the metals composition range of 55–84 cation% indium, the as‐deposited IZO thin films are amorphous, smooth (R_RMS < 0.4 nm), conductive (σ ∼ 3000 Ω⁻¹ · cm⁻¹), and transparent in the visible (T_Vis > 90%). Furthermore, the amorphous IZO thin films demonstrate remarkable functional and structural stability with respect to heating up to 600 °C in either air or argon. Hence, though not completely understood at present, these amorphous materials constitute a new class of fundamentally interesting and technologically important high performance transparent conductors.     

Interface engineering and characterization at the atomic‐scale of pure and mixed ion layer gas reaction buffer layers in chalcopyrite thin‐film solar cells

In this work, we investigate the p–n junction region for two different buffer/Cu(In,Ga)(Se,S)₂ (CIGSSe) samples having different conversion efficiencies (the cell with pure In₂S₃ buffer shows a lower efficiency than the nano‐ZnS/In₂S₃ buffered one). To explain the better efficiency of the sample with nano‐ZnS/In₂S₃ buffer layer, combined transmission electron microscopy, atom probe tomography, and X‐ray photoelectron spectroscopy studies were performed. In the pure In₂S₃ buffered sample, a CuIn₃Se₅ ordered‐defect compound is observed at the CIGSSe surface, whereas in the nano‐ZnS/In₂S₃ buffered sample no such compound is detected. The absence of an ordered‐defect compound in the latter sample is explained either by the presence of the ZnS nanodots, which may act as a barrier layer against Cu diffusion in CIGSSe hindering the formation of CuIn₃Se₅, or by the presence of Zn at the CIGSSe surface, which may disturb the formation of this ordered‐defect compound. In the nano‐ZnS/In₂S₃ sample, Zn was found in the first monolayers of the absorber layer, which may lead to a downward band bending at the surface. This configuration is very stable (Fermi level pinning at the conduction band, as observed for Cd in Cu(In,Ga)Se₂) and reduces the recombination rate at the interface. This effect may explain why the sample with ZnS nanodots possesses a higher efficiency. This work demonstrates the capability of correlative transmission electron microscopy, atom probe tomography, and X‐ray photoelectron spectroscopy studies in investigating buried interfaces. The study provides essential information for understanding and modeling the p–n junction at the nanoscale in CIGSSe solar cells. Copyright © 2014 John Wiley & Sons, Ltd.     

Thin Al2O3 passivated boron emitter of n‐type bifacial c‐Si solar cells with industrial process

We have presented thin Al₂O₃ (~4 nm) with SiN_x:H capped (~75 nm) films to effectively passivate the boron‐doped p⁺ emitter surfaces of the n‐type bifacial c‐Si solar cells with BBr₃ diffusion emitter and phosphorus ion‐implanted back surface field. The thin Al₂O₃ capped with SiN_x:H structure not only possesses the excellent field effect and chemical passivation, but also establishes a simple cell structure fully compatible with the existing production lines and processes for the low‐cost n‐type bifacial c‐Si solar cell industrialization. We have successfully achieved the large area (238.95 cm²) high efficiency of 20.89% (front) and 18.45% (rear) n‐type bifacial c‐Si solar cells by optimizing the peak sintering temperature and fine finger double printing technology. We have further shown that the conversion efficiency of the n‐type bifacial c‐Si solar cells can be improved to be over 21.3% by taking a reasonable high emitter sheet resistance. Copyright © 2017 John Wiley & Sons, Ltd.     

Highly‐efficient Cd‐free CuInS2 thin‐film solar cells and mini‐modules with Zn(S,O) buffer layers prepared by an alternative chemical bath process

Recent progress in fabricating Cd‐ and Se‐free wide‐gap chalcopyrite thin‐film solar devices with Zn(S,O) buffer layers prepared by an alternative chemical bath process (CBD) using thiourea as complexing agent is discussed. Zn(S,O) has a larger band gap (E_g = 3·6–3·8 eV) than the conventional buffer material CdS (E_g = 2·4 eV) currently used in chalcopyrite‐based thin films solar cells. Thus, Zn(S,O) is a potential alternative buffer material, which already results in Cd‐free solar cell devices with increased spectral response in the blue wavelength region if low‐gap chalcopyrites are used. Suitable conditions for reproducible deposition of good‐quality Zn(S,O) thin films on wide‐gap CuInS₂ (‘CIS’) absorbers have been identified for an alternative, low‐temperature chemical route. The thickness of the different Zn(S,O) buffers and the coverage of the CIS absorber by those layers as well as their surface composition were controlled by scanning electron microscopy, X‐ray photoelectron spectroscopy, and X‐ray excited Auger electron spectroscopy. The minimum thickness required for a complete coverage of the rough CIS absorber by a Zn(S,O) layer deposited by this CBD process was estimated to ∼15 nm. The high transparency of this Zn(S,O) buffer layer in the short‐wavelength region leads to an increase of ∼1 mA/cm² in the short‐circuit current density of corresponding CIS‐based solar cells. Active area efficiencies exceeding 11·0% (total area: 10·4%) have been achieved for the first time, with an open circuit voltage of 700·4 mV, a fill factor of 65·8% and a short‐circuit current density of 24·5 mA/cm² (total area: 22·5 mA/cm²). These results are comparable to the performance of CdS buffered reference cells. First integrated series interconnected mini‐modules on 5 × 5 cm² substrates have been prepared and already reach an efficiency (active area: 17·2 cm²) of above 8%. Copyright © 2006 John Wiley & Sons, Ltd.     

Surface passivation of high‐efficiency silicon solar cells by atomic‐layer‐deposited Al2O3

Atomic‐layer‐deposited aluminium oxide (Al₂O₃) is applied as rear‐surface‐passivating dielectric layer to passivated emitter and rear cell (PERC)‐type crystalline silicon (c‐Si) solar cells. The excellent passivation of low‐resistivity p‐type silicon by the negative‐charge‐dielectric Al₂O₃ is confirmed on the device level by an independently confirmed energy conversion efficiency of 20·6%. The best results are obtained for a stack consisting of a 30 nm Al₂O₃ film covered by a 200 nm plasma‐enhanced‐chemical‐vapour‐deposited silicon oxide (SiO_x) layer, resulting in a rear surface recombination velocity (SRV) of 70 cm/s. Comparable results are obtained for a 130 nm single‐layer of Al₂O₃, resulting in a rear SRV of 90 cm/s. Copyright © 2008 John Wiley & Sons, Ltd.     

Improved Interface and Electrical Properties by Inserting an Ultrathin SiO2 Buffer Layer in the Al2O3/Si Heterojunction

An ultrathin SiO₂ interfacial buffer layer is formed using the nitric acid oxidation of Si (NAOS) method to improve the interface and electrical properties of Al₂O₃/Si, and its effect on the leakage current and interfacial states is analyzed. The leakage current density of the Al₂O₃/Si sample (8.1 × 10^?9 A cm^?2) due to the formation of low‐density SiO_x layer during the atomic layer deposition (ALD) process, decreases by approximately two orders of magnitude when SiO₂ buffer layer is inserted using the NAOS method (1.1 × 10^?11 A cm^?2), and further decreases after post‐metallization annealing (PMA) (1.4 × 10^?12 A cm^?2). Based on these results, the influence of interfacial defect states is analyzed. The equilibrium density of defect sites (N_d) and fixed charge density (N_f) are both reduced after NAOS and then further decreased by PMA treatment. The interface state density (D_it) at 0.11 eV decreases about one order of magnitude from 2.5 × 10¹² to 7.3 × 10¹¹ atoms eV^?1 cm^?2 after NAOS, and to 3.0 × 10¹⁰ atoms eV^?1 cm^?2 after PMA. Consequently, it is demonstrated that the high defect density of the Al₂O₃/Si interface is drastically reduced by fabricating ultrathin high density SiO₂ buffer layer, and the insulating properties are improved.     

A Novel Mesoporous CaO‐Loaded In2O3 Material for CO2 Sensing

A mesoporous CaO‐loaded In₂O₃ material (with Ca/In₂O₃ ratios ranging from 2.5 to 8.5 at %) has been synthesized and used as resistive gas sensor for the detection of CO₂. A nanostructured In₂O₃ matrix has been obtained by hard template route from the SBA‐15 silica template. Additive presence does not distort the lattice of In₂O₃, which crystallizes in the Ia3 cubic space group. It has been proved by XRD, HRTEM, Raman and XPS measurements that samples contain not only CaO but also CaCO₃ in calcite phase as a consequence of CaO carbonation. Pure In₂O₃ based sensors are low sensitive to CO₂, whereas those containing the additive show an important response in the 300–5000 ppm range of gas concentrations. As seen by DRIFTS, the electrical response arises from the interaction between CO₃^2– and CO₂, yielding bicarbonates products. The reaction is water‐assisted, so that hydration of the sensing material ensures sensor reliability whilst its dehydration would inhibit sensor response. The use of CaCO₃ instead of CaO does not cause significant differences in electrical and DRIFTS data, which corroborates the important role played by carbonate species in the sensing mechanism.     

Process Pathway Controlled Evolution of Phase and Van‐der‐Waals Epitaxy in In/In2O3 on Graphene Heterostructures

Many applications of 2D materials require deposition of non‐2D metals and metal‐oxides onto the 2D materials. Little is however known about the mechanisms of such non‐2D/2D interfacing, particularly at the atomic scale. Here, atomically resolved scanning transmission electron microscopy (STEM) is used to follow the entire physical vapor deposition (PVD) cycle of application‐relevant non‐2D In/In₂O₃ nanostructures on graphene. First, a “quasi‐in‐situ” approach with indium being in situ evaporated onto graphene in oxygen‐/water‐free ultra‐high‐vacuum (UHV) is employed, followed by STEM imaging without vacuum break and then repeated controlled ambient air exposures and reloading into STEM. This allows stepwise monitoring of the oxidation of specific In particles toward In₂O₃ on graphene. This is then compared with conventional, scalable ex situ In PVD onto graphene in high vacuum (HV) with significant residual oxygen/water traces. The data shows that the process pathway difference of oxygen/water feeding between UHV/ambient and HV fabrication drastically impacts not only non‐2D In/In₂O₃ phase evolution but also In₂O₃/graphene out‐of‐plane texture and in‐plane rotational van‐der‐Waals epitaxy. Since non‐2D/2D heterostructures' properties are intimately linked to their structure and since influences like oxygen/water traces are often hard to control in scalable fabrication, this is a key finding for non‐2D/2D integration process design.     

Studies in CuInS2 based solar cells,including ZnS and In2S3 buffer layers

The influence of the growth conditions on the surface chemistry and on the homogeneity of the chemical composition of CuInS₂ (CIS) thin films, prepared by sequential evaporation of metallic precursors in presence of elemental sulfur in a two-stage process, was studied by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It was found that the growth temperature affects the phase in which this compound grows. The samples deposited at temperatures around 500 °C (2nd stage) contain mainly the CuInS₂ phase; however, secondary phases like In₂S₃, Cu₂S were additionally identified at the surface and in the bulk of CuInS₂ samples deposited at temperatures greater than 550 °C. Also, the elemental composition of the layers constituting the Glass/Mo/CuInS₂/buffer/ZnO structure was studied through Auger electron spectroscopy (AES) depth profile measurements. AES measurements carried out across the Glass/Mo/CuInS₂/buffer/ZnO heterojunction gave evidence of Cu diffusion from the CuInS₂ layer towards the rest of the layers constituting the device, and of the formation of a MoS₂ layer in the Mo/CuInS₂ interface. The performance of CuInS₂-based solar cells fabricated using CBD (chemical bath deposition) deposited ZnS as buffer layer was compared to that of cells fabricated using CBD deposited In₂S₃ as buffer.     

Electrical conduction in thin films based on In2O3 and In2O3/CeO2

Electrical measurements on thin films of In₂O₃ and In₂O₃/CeO₂ before and after electroforming are reported. The high field conduction (expressed in terms of circulating current I _c and base voltage V _b) in thin film sandwich structures (MIM, Metal-Insulator-Metal) of Cu-In₂O₃-Cu and Cu-In₂O₃/CeO₂-Cu is found to obey a relation of the form log I _cαV _b ^½. The electroformed samples show voltage controlled negative resistance (VCNR). Voltage memory, thermal voltage memory and pressure voltage memory effects are observed and the results are explained in terms of the filamentory model of electrical conduction.