Photovoltaic Absorber Material Research Articles

Influence of PVP on the properties of solvothermally synthesized famatinite nanoparticles: Structural, morphological and optical insights

Famatinite (Cu3SbS4) nanoparticles were synthesized through a solvothermal approach using various polyvinylpyrrolidone (PVP) ratios as a capping agent with a binary solvent of ethylene glycol and water in equal parts. Incremental additions of PVP, ranging from 0 to 1.5 g, exerted significant influence on the material's characteristics. Through comprehensive analysis involving X-ray diffraction, Raman spectroscopy, Scanning electron microscopy (SEM) with Energy dispersive spectrometer (EDS), and UV diffuse reflectance spectroscopy, critical insights were obtained. XRD analysis confirmed the tetragonal crystal structure and revealed reduced crystallite sizes due to the incorporation of PVP. Raman spectroscopy validated the presence of pure famatinite phase with 0.5 g and 1.0 g PVP. SEM analysis uniformly depicted a spherical morphology in all samples, emphasizing PVP's role in mitigating nanoparticle agglomeration. UV diffuse reflectance spectroscopy disclosed direct bandgaps falling within the 0.88 – 0.97 eV range. The collective findings highlighted the substantial impact of PVP in the binary solvent on the structural, morphological, and optical properties of Cu3SbS4 nanoparticles. These results underscore the potential application of these tailored nanoparticles as promising candidates for advanced photovoltaic absorber materials.

Influence of Sulfurization Time on Sb2S3 Synthesis Using a New Graphite Box Design.

In recent years, antimony sulfide (Sb2S3) has been investigated as a photovoltaic absorber material due to its suitable absorber coefficient, direct band gap, extinction coefficient, earth-abundant, and environmentally friendly constituents. Therefore, this work proposes Sb2S3 film preparation by an effective two-step process using a new graphite box design and sulfur distribution, which has a high repeatability level and can be scalable. First, an Sb thin film was deposited using the RF-Sputtering technique, and after that, the samples were annealed with elemental sulfur into a graphite box, varying the sulfurization time from 20 to 50 min. The structural, optical, morphological, and chemical characteristics of the resulting thin films were analyzed. Results reveal the method's effectivity and the best properties were obtained for the sample sulfurized during 40 min. This Sb2S3 thin film presents an orthorhombic crystalline structure, elongated grains, a band gap of 1.69 eV, a crystallite size of 15.25 Å, and a nearly stoichiometric composition. In addition, the formation of a p-n junction was achieved by depositing silver back contact on the Glass/FTO/CdS/Sb2S3 structure. Therefore, the graphite box design has been demonstrated to be functional to obtain Sb2S3 by a two-step process.

Fabrication and Characterization of a Lead-Free Cesium Bismuth Iodide Perovskite through Antisolvent-Assisted Crystallization.

Cesium bismuth iodide perovskite material offers good stability toward ambient conditions and has potential optoelectronic characteristics. However, wide bandgap, absorber surface roughness, and poor surface coverage with pinholes are among the key impediments to its adoption as a photovoltaic absorber material. Herein, bandgap modification and the tailoring of surface morphology have been performed through molar ratio variation and antisolvent treatment, whereby type III antisolvent (toluene) based on Hansen space has been utilized. XRD and Raman spectroscopy analyses confirm the formation of a 0D/2D mixed dimensional structure with improved optoelectronic properties when the molar ratio of CsI/BiI3 was adjusted from 1.5:1 to 1:1.5. The absorption results and Tauc plot determination show that the fabricated film has a lower bandgap of 1.80 eV. TRPL analysis reveals that the film possesses a very low charge carrier lifetime of 0.94 ns, suggesting deep defects. Toluene improves the charge carrier lifetime to 1.89 ns. The average grain size also increases from 323.26 nm to 444.3 nm upon toluene addition. Additionally, the inclusion of toluene results in a modest improvement in PCE, from 0.23% to 0.33%.

Regulating the crystal orientation of vapor-transport-deposited GeSe thin films by a post-annealing treatment

Recently, GeSe has emerged as a highly promising photovoltaic absorber material due to its excellent optoelectronic properties, nontoxicity, and high stability. Although many advantages make GeSe well suited for thin-film solar cells, the power conversion efficiency of the GeSe thin-film solar cell is still much below the theoretical maximum efficiency. One of the challenges lies in controlling the crystal orientation of GeSe to enhance solar cell performance. The two-step preparation of GeSe thin films has not yet been reported to grow along the [111] orientation. In this work, we study the effect of a post-annealing treatment on the GeSe thin films and the performance of the solar cells. It was found that amorphous GeSe films can be converted into polycrystalline films with different orientations by changing the post-annealing temperature. [111]-oriented and [100]-oriented GeSe thin films were successfully prepared on the same substrate by optimizing the annealing conditions. With the structure of Au/GeSe/CdS/ITO cell devices, PCEs of 0.14% and 0.16% were ultimately achieved.

Accurate and rapid predictions with explainable graph neural networks for small high-fidelity bandgap datasets

Accurate and rapid bandgap prediction is a fundamental task in materials science. We propose graph neural networks with transfer learning to overcome the scarcity of training data for high-fidelity bandgap predictions. We also add a perturbation-based component to our framework to improve explainability. The experimental results show that a framework consisting of graph-level pre-training and standard fine-tuning achieves superior performance on all high-fidelity bandgap prediction tasks and training-set sizes. Furthermore, the framework provides a reliable explanation that considers node features together with the graph structure. We also used the framework to screen 105 potential photovoltaic absorber materials.

Performance evaluation of 2D MoS2-based solar cells and realization of transparent ultra-thin devices

Molybdenum disulfide (MoS2) is an alternate absorber layer in 2D solar cells owing to its potential of proficient sunlight harvesting. The optimum electrical and optical properties of MoS2 validate it as a suitable photovoltaic absorber material. This work investigates the performance of 2D (and multi-layer) MoS2-based vertically stacked solar cell by numerical simulation process using one dimensional solar cell capacitance simulator (SCAPS). Two device configurations based on Schottky junction (ITO/n-MoS2/Au) and pn junction (ITO/n-MoS2/p-MoS2/Au) have been theoretically analyzed. The feasibility of ultra-thin transparent solar cells is also demonstrated, which is motivating from a technological outlook. Initially, the properties of the active layers are optimized to give the highest performance. The findings are explained on the basis of band alignment between the electrodes and the different layers. The potential barrier developed at the interface of different materials governs the output of the cells. The calculations forecast the material properties, which need to be tuned to fabricate solar cells with enhanced efficiency. After optimization, the highest efficiency obtained for single n-MoS2-based solar cell is 10.22%, while for the pn junction solar cell it is 16.86%. The optimized cells exhibit high open circuit voltages of ∼1.2 V, which is an essential factor for commercial realization of solar cells. Lastly, the performance of transparent solar cells based on thin 2D MoS2 films has been predicted which showcases the efficiency in the range of 0.78%–4.36%. These homo-junction device investigations of solely MoS2 layer along with employment of a strict control on the defects during deposition and fabrication of MoS2-based solar cells can ensure better performance of the device. Thus, it can open ways to develop next generation feasible solar cells with higher power density as compared to existing technology.

Stability and electronic properties of ‘4-8’-type ZnSnN2 thin films free of spontaneous polarization for optoelectronic applications

Ternary nitride ZnSnN2 is a promising photovoltaic absorber material. In this work, we using first-principles calculations investigate the stability and electronic properties of ‘4–8’-type ZnSnN2 thin films. We find that below a certain thickness ‘4–8’-type thin films have lower total energy than polar films in the wurtzite-derived structures. For 4-layer ZnSnN2 thin film, the Pna21/Pmc21 → 4–8 transitions can spontaneously occur at finite temperatures. All ‘4–8’-type thin films studied are semiconducting and free of spontaneous polarization, the bandgap of which can be tuned by the thickness of films, ranging from 1.4 eV to 1.8 eV. Furthermore, these films show light electron effective masses, and octet-rule-preserving disorder has insignificant effects on the electronic properties. Our results provide new insights into the structure of ZnSnN2 in the thin film form and guidance for the experimental investigation.

Theoretical Investigation of Delafossite-Cu2ZnSnO4 as a Promising Photovoltaic Absorber.

In the quest for efficient and cost-effective photovoltaic absorber materials beyond silicon, considerable attention has been directed toward exploring alternatives. One such material, zincblende-derived Cu2ZnSnS4 (CZTS), has shown promise due to its ideal band gap size and high absorption coefficient. However, challenges such as structural defects and secondary phase formation have hindered its development. In this study, we examine the potential of another compound, Cu2ZnSnO4 (CZTO), with a similar composition to CZTS as a promising alternative. Employing ab initio density function theory (DFT) calculations in combination with an evolutionary structure prediction algorithm, we identify that the crystalline phase of delafossite structure is the most stable among the 900 (meta)stable CZTO. Its thermodynamic stability at room temperature is also confirmed by the molecular dynamics study. Excitingly, this new phase of CZTO displays a direct band gap where the dipole-allowed transition occurs, making it a strong candidate for efficient light absorptions. Furthermore, the estimation of spectroscopic limited maximum efficiency (SLME) directly demonstrates the high potential of delafossite-CZTO as a photovoltaic absorber. Our numerical results suggest that delafossite-CZTO holds promise for future photovoltaic applications.

The quest for optimal photovoltaics: A theoretical exploration of quasi-one-dimensional tin based chalcogenides XSnS[formula omitted] (X=Ba, Sr)

Structural, mechanical, electronic, and optical properties of alkaline metals (Ba, Sr) tin chalcogenide were investigated by the first principles method based on density functional theory (DFT) implemented in the WEIN2K program. The study found that both materials exhibit a quasi-one-dimensional nature along the b-axis, and the optimized structure agrees with the available experimental data. Mechanical properties revealed that both materials are mechanically stable, exhibit ductility, and have significant anisotropy. BaSnS3 and SrSnS3 exhibit an indirect band gap with the values of 1.55 eV and 1.39 eV, respectively. Which is favorable for photovoltaic solar cell absorber materials. Like many ternary metal chalcogenides, XSnS3 compounds show significant anisotropy in the optical properties due to their quasi-one-dimensional structure. This work determined the degree of optical anisotropy of XSnS3 in terms of the dielectric function, refractive index, optical absorption, reflectivity, optical extinction, birefringence, and energy loss function. The results indicate that BaSnS3 and SrSnS3 materials possess notable optical anisotropy and a high absorption coefficient (α≈106 cm−1), low reflectivity and energy loss function within the visible and ultraviolet energy range. It indicates their potential for use in a range of applications, such as sensors, optoelectronics, and photovoltaic solar cell absorber materials.

A CTL-free homo-heterojunction antimony chalcogenide solar cell: Theoretical study

Exploring antimony chalcogenide as photovoltaic (PV) absorber material for solar cell is an appealing strategy. However, the conversion efficiency (η) of antimony chalcogenide solar cells including antimony selenide (Sb2Se3), antimony sulfide (Sb2S3) and antimony sulfide–selenide (Sb2(S,Se)3) lag far behind their Shockley−Queisser limit efficiency. Generally, the device PV performance of thin film heterojunction solar cells is mainly affected by the material properties of each functional layer, as well as the device architecture and heterointerface characteristics. Herein, a novel homo-heterojunction antimony chalcogenide solar cell without any carrier transport layer (CTL) consisting of FTO/(n)Sb2Se3/(p)Sb2Se3/(p)Sb2S3/Metal has been proposed. The influence of thickness, doping concentration and bulk defect density of the functional layer materials, the interface defect density at (p)Sb2Se3/(p)Sb2S3 heterointerfaces, and back contact metal work function on device PV performance have been theoretically analyzed utilized wxAMPS software. After optimization, the proposed solar cell has an open-circuit voltage (Voc) of 0.885 V, a short-circuit current density (Jsc) of 36.14 mAcm−2, a filling factor (FF) of 84.30 %, and a η of 26.97 %. These results indicate that the novel homo-heterojunction antimony chalcogenide solar cell without any CTL have the potential to become a high-efficiency PV device.

Effect of Adding Cu2O as a Back Surface Field Layer on the Performance of Copper Manganese Tin Sulfide Solar Cells

One of the major limitations causing deadlock in solar cells with higher sulfur content in the photovoltaic absorber material is the unintended formation of an uncontrollable MoS2 layer between the absorber material and Mo back contact, which can affect negatively the efficiency of solar cells. Researchers reported that it is very difficult to control the MoS2 properties such as the conductivity type, thickness, band gap, and carrier concentration in experiments. Considering these challenges, an initial step involved a thorough examination utilizing the one-dimensional solar cell capacitance simulator (SCAPS-1D) to assess the impact of n-MoS2 interlayer thickness and donor concentration on the performance of CMTS solar cells. Our investigation revealed the formation of a “cliff-like CBO” at the CMTS/n-MoS2 interface, facilitating the transport of electrons from the p-CMTS absorber to the Mo back contact, resulting in a significantly higher recombination rate. Subsequently, herein a novel approach is proposed, using Cu2O as a back surface field (BSF) layer due to its low cost, intrinsic p-type properties, and non-toxic nature. Simulation results of a novel heterostructure (Mo/Cu2O/CMTS/CdS/i-ZnO/AZO/Al) of the CMTS-based solar cell are discussed in terms of recombination rate and conduction band alignment at the absorber/BSF interface. A desired “spike-like CBO” is formed between CMTS/Cu2O, which hinders the transport of electrons to the back contact. By optimizing the physical parameters such as thickness and the doping density of the Cu2O layer, an efficiency η of 21.78% is achieved, with an open circuit voltage (Voc) of 1.26 V, short-circuit current density (Jsc) of 24.45 mA/cm², and fill factor (FF) of 70.85%. Our simulation results offer a promising research direction to further develop highly efficient and low-cost CMTS solar cells.

Performance Analysis of CdS‐Free, Sb2Se3/ZnSe p–n Junction Cells with Various Hole Transport Layers and Contacts

AbstractSb2Se3, a promising thin‐film photovoltaic (TFPV) absorber material known for its non‐toxic nature, abundance on Earth, and stability has the inherent limitations of low doping density of 1013 cm−3 and poor carrier mobility of 1.5 cm2 V−1 s−1, leading to a low built‐in potential and inefficient carrier collection. To address these challenges and enhance the built‐in potential and carrier collection, an effective hole‐transport layer (HTL), e.g. CdS, which contains toxic components is used. A less‐toxic alternative is explored: ZnSe as the electron‐transport layer (ETL) to mitigate this issue. In this study, the performance is evaluated of Sb2Se3/ZnSe solar cells using six different HTLs (CuSCN, MoSe2, NiO, Spiro‐OMeTAD, SnS, MoOx) through the utilization of the SCAPS‐1D modeling tool. The HTL plays a critical role in improving the effectiveness of the built‐in potential, enhancing carrier collection, and suppressing back surface recombination. The analysis involves varying the thickness and doping concentration of the absorber, buffer, and HTLs, and exploring the impact of temperature, series and shunt resistance, and the metal work function of the back contact. Among the tested devices, the one with NiO as the HTL demonstrates the highest efficiency, exhibiting a VOC (open‐circuit voltage) of 0.81 V and a PCE (power conversion efficiency) of 24.07%.

Computational investigation of inverse perovskite SbPX3 (X = Mg, Ca, and Sr) structured materials with applicability in green energy resources

With the exchange of ionic positions, antiperovskites (inverse perovskites) have maintained the perovskite crystal structure. Inverse perovskites offer interesting photovoltaic applications as they have a low band gap, strong absorption, and low cost. To confirm the stability, we have calculated some stability parameters firstly, such as structural, elastic, and thermodynamic parameters. The proposed materials are highly stable. We further calculated its optoelectronic and thermoelectric characteristics to substantiate its potential uses in green energy. All of these characteristics are determined using the Density Functional Theory simulation tool WIEN2k. We have utilized Spectroscopic Limited Maximum Efficiency (SLME) to test the theoretical power conversion efficiency of the proposed materials. Eventually, it is clear that these materials are extremely stable and have substantial absorption in the VIS, UV, and NIR bands, which is a commendable attribute gained by a variety of optoelectronic devices. The proposed antiperovskite SbPMg3 with SLME 15.8%, is expected to be a stable yet efficient photovoltaic absorber material. Since the figure of merit of the suggested materials approaches unity, they can also be employed in thermoelectric generators.

Alkaline earth based antiperovskite AsPX3 (X = Mg, Ca, and Sr) materials for energy conversion efficient and thermoelectric applications

Antiperovskite were created by swapping ionic positions in the perovskite ABX3 crystal composition. These have great potential for renewable energy devices owing to their low band gap, low cost, and high absorption with Pm-3m space group. Herein, the authors have investigated inherent properties such as bulk modulus and its pressure derivatives, lattice constant, the density of states, band gap, effective mass, refractive index, dielectric constant, extinction coefficient, and absorption coefficient, thermoelectric parameters etc of antiperovskite materials by using density functional theory-based first-principles calculations. These materials exhibit high absorption in the Visible, Ultraviolet region and also in the Near Infrared region which is the most admirable property acquired by various Optoelectronic devices. The proposed compounds have been found mechanically and thermodynamically stable. Their high figure of merit makes them a potential candidate for thermoelectric devices. The proposed material AsPCa3 with a theoretical efficiency of 34% is expected to be a good photovoltaic absorber material.

Post deposition annealing effect on properties of CdS films and its impact on CdS/Sb2Se3 solar cells performance

Antimony selenide (Sb2Se3) is one of the emerging photovoltaic absorber materials possessing abundance and non-toxicity as the main attributes. Following CdTe technology, CdS is a widely used partner layer for Sb2Se3 solar cells. Related to CdS/Sb2Se3 device configuration, a number of studies reported findings and challenges regarding the intermixing phenomenon at the main interface and suitability of various annealing for CdS (and related interface) and still, significant room remains in developing strategies for interface optimization and understanding of the physiochemistry behind. In this perspective, this work provides a systematic investigation of the effect of vacuum and air annealing at temperatures between 200 and 400°C on the properties of CdS deposited by chemical bath deposition and combined with Sb2Se3 absorber obtained by close-spaced sublimation the direct impact of the CdS annealing on the device performance is illustrated. It is found that by varying the annealing temperature from 200 to 400°C in both, vacuum and air ambient, the morphology of CdS changes from highly dispersed small grain structure to sintered dense grains, the band gap decreases from 2.43 to 2.35 eV and the electron density drops from ∼1018 to ∼1011 cm−3. These changes were correlated with the changes in the CdS lattice and connected with the mobility of the OH group and the presence of secondary phases in CdS layers. 200°C air annealing of CdS was found as an optimal treatment resulting in 2.8% Sb2Se3/CdS cell efficiency - a 60% boost compared to the 1.8% performance of the device with as-deposited CdS. Material and device characterization analysis is performed, providing complementary insights on the interrelation between the physicochemical mechanism of the CdS annealing processes and device functionality.

Prospects for inorganic CsPbI3 perovskite solar cells with commercially viable lifetimes

Perovskite CsPbI3 is a promising photovoltaic absorber material, thanks to its ideal bandgap for Si-tandem solar cell applications and its excellent thermochemical stability compared with hybrid organic–inorganic perovskites. However, CsPbI3 has its own stability challenges as its photoactive β- and γ-polymorphs are thermodynamically unstable at room temperature compared with the yellow non-perovskite δ-phase. Stabilizing CsPbI3 has, thus, been the subject of considerable research in recent years. While some approaches, such as alloying with halides and reducing crystalline domain size, have proven effective in improving phase stability, these benefits have, thus far, come at the expense of photovoltaic efficiency compared with the state-of-the-art CsPbI3 solar cells. In this perspective, we discuss the progress and limitations of inorganic perovskite stabilization techniques and look forward at how to achieve inorganic perovskite solar cells with both commercially viable efficiencies and lifetimes.

Photochemical Decomposition of Y‐Series Non‐Fullerene Acceptors Is Responsible for Degradation of High‐Efficiency Organic Solar Cells

AbstractOrganic photovoltaic cells that employ Y‐series non‐fullerene acceptors (NFAs) have recently achieved impressive power‐conversion efficiencies (>18%). To fulfill their commercial promise, it is important to quantify their operational lifetimes and understand their degradation mechanisms. In this work, the spectral‐dependent photostability of films and solar cells comprising several Y‐series acceptors and the donor polymer PM6 is investigated systematically. By applying longpass filters during aging, it is shown that UV/near‐UV photons are responsible for the photochemical decomposition of Y‐series acceptors; this degradation is the primary driver of early solar cell performance losses. Using mass spectrometry, the vinylene linkage between the core and electron‐accepting moieties of Y‐series acceptors is identified as the weak point susceptible to cleavage under UV‐illumination. Employing a series of device characterization, along with numerical simulations, the efficiency losses in organic photovoltaic cells are attributed to the formation of traps, which reduces charge extraction efficiency and facilitates non‐radiative recombination as the Y‐series acceptors degrade. This study provides new insights for molecular degradation of organic photovoltaic absorber materials and highlights the importance of future molecular design and strategies for improved solar cell stability.

Enhanced photoresponse of Cu2ZnSnS4 absorber thin films fabricated using multi-metallic stacked nanolayers.

Cu2ZnSnS4 (CZTS) thin films have attracted considerable attention as potential candidates for photovoltaic absorber materials. In a vacuum deposition technique, a sputtering stacked metallic layer followed by a thermal process for sulfur incorporation is used to obtain high-quality CZTS thin films. In this work, for fabricating CZTS thin films, we have done a 3LYS (3 layers), 6LYS, and 9LYS sequential deposition of Sn/ZnS/Cu metal stack (via. metallic stacked nanolayer precursors) onto Mo-coated corning glass substrate via. RF-sputtering. The prepared thin films were sulfurized in a tubular furnace at 550 °C in a gas mixture of 5% H2S + 95% Ar for 10 min. We further investigated the impact of the Sn/ZnS/Cu metal stacking layers on the quality of the thin film based on its response to light because metal inter-diffusion during sulfurization is unavoidable. The inter-diffusion of precursors is low in a 3-layer stack sample, limiting the fabricated film's performance. CZTS films with 6-layer and 9-layer stacks result in an improved photocurrent density of ∼38 μA cm-2 and ∼82 μA cm-2, respectively, compared to a 3-layer sample which has a photocurrent density of ∼19 μA cm-2. This enhancement can be attributed to the 9-layer approach's superior inter-diffusion of metallic precursors and compact, smooth CZTS microstructure evolution.

Performance investigation of antimony chalcogenide based thin film solar cells via SCAPS simulation

Antimony chalcogenides thin films are promising photovoltaic absorber materials because of non-toxic and earth-abundant constituents. However, antimony chalcogenide based solar cells have yet to realize efficient performance compared with perovskite or CIGS based solar cells. In this work, a numerical simulation of Sb2(S1−xSex)3 thin films solar cells were investigated using one dimensional Solar Capacitance Simulator (SCAPS-1D). The solar cells parameters such as work temperature, defect density, electrode work function and band structure were investigated to determine the impact on device performance. The results show that compared with other device parameters, the main factors affecting device performance are band structure and defect concentration. By optimizing the parameters of the solar cell, the device efficiency is significantly improved from 9.08 % to 15.19 %. By preparing absorber layers with gradient band gap, reducing the defect density can significantly improve the device performance. These results contribute to the design and fabrication of efficient low-cost thin film solar cells and provide theoretical basis.

Sputtering Al2O3 as an effective interface layer to improve open-circuit voltage and device performance of Sb2Se3 thin-film solar cells

Sb2Se3 as a promising photovoltaic absorber material is attracting increasing attention. However, high open-circuit voltage (VOC) loss, especially for superstrate structured Sb2Se3 solar cells, is one of the main bottlenecks for improving device efficiency. Here, sputtering aluminum oxide (Al2O3) as an interface layer between CdS and Sb2Se3 was applied in superstrate structured Sb2Se3 solar cells. We proved that the sputtered Al2O3 layer is not fully continuous on the rough CdS film even its thickness has reached 8.8 nm. Then we systematically investigated the influence of the Al2O3 layer on Sb2Se3 material properties and device performances. It is found that the Al2O3 layer can not only effectively inhibit [hk0]-oriented crystal growth and promote [hk1] growth orientation of Sb2Se3 films but also obviously weaken the disordered growth of prominent petal-like shape Sb2Se3 grains and reduce the surface roughness. Further, the Al2O3 layer can also availably passivate interfacial defects at the CdS/Sb2Se3 interface. Consequently, the average power conversion efficiency (PCE) of Sb2Se3 solar cells with an optimal Al2O3 layer thickness is 17.86% higher than that without the Al2O3 layer. Noteworthily, the VOC of Sb2Se3 solar cells is boosted to 0.462 V, which is the highest value in superstrate structured Sb2Se3 solar cells with absorber prepared by conventional physical methods. Finally, a champion efficiency of 6.25% has been achieved in a low-cost Sb2Se3 thin-film solar cell with FTO/CdS/Al2O3/Sb2Se3/Carbon device configuration.