Lithium garnet solid electrolytes such as Li₇La₃Zr₂O₁₂ (LLZO) are widely regarded as promising candidates for next-generation all-solid-state lithium batteries owing to their high ionic conductivity, wide electrochemical stability window, and superior mechanical stiffness against lithium dendrite penetration. These attributes position LLZO as a key advanced energy material for enabling safe, high-energy-density storage technologies critical to electrified transportation and renewable energy integration. However, despite frequently being approximated as purely Ohmic ionic conductors, growing experimental evidence indicates that transport in LLZO can deviate significantly from ideal electroneutral behavior. In particular, interfacial resistance, thickness-dependent conductivity, and current-induced polarization effects have been reported to limit rate capability and power performance in practical cells.

In this work, we develop a continuum-scale theoretical framework to systematically investigate lithium-ion transport in LLZO under externally applied electric fields. The model is formulated using the coupled Poisson–Nernst–Planck (PNP) equations, capturing the interplay between ionic diffusion, migration, and electrostatic potential evolution. The governing equations are nondimensionalized using physically motivated scaling parameters, revealing that the transport response is governed primarily by a single dimensionless group corresponding to the squared ratio of the Debye screening length to the electrolyte thickness. This scaling provides direct physical insight into when space-charge effects become non-negligible in solid electrolytes.

To resolve the resulting nonlinear boundary-value problem, numerical solutions are obtained using a fully implicit Newton–Raphson scheme, enabling stable and accurate resolution of steep potential gradients and space-charge layers near blocking or reactive interfaces. The simulations reveal pronounced deviations from classical Ohmic conduction in thin electrolytes and under high applied voltages, manifested through charge accumulation, field localization, and nonlinear current–voltage characteristics. These findings demonstrate that polarization losses in LLZO cannot always be attributed solely to microstructural defects or grain boundary resistance but may arise intrinsically from continuum electrostatic effects.

The developed framework establishes a quantitative basis for interpreting experimental impedance and polarization data and provides design guidelines for thickness optimization, interfacial engineering, and composite electrolyte architectures. More broadly, this study highlights the importance of coupled electrochemical–electrostatic modeling in advancing solid-state battery performance and reliability.

Polymer-based thermoelectric materials offer several advantages compared to conventional metal oxides (like bismuth telluride (Bi₂Te₃), lead telluride (PbTe), silicon germanium (SiGe), and bismuth antimony telluride (BiSbTe) alloys), including enhanced availability, cost efficiency, ease of processing, mechanical flexibility, low density, and reduced thermal conductivity. The incorporation of these materials into flexible and wearable electronics is a straightforward process that gives rise to the possibility of energy harvesting from body heat or other low-grade heat sources. If SWCNTs are combined with other materials, interfaces can scatter phonons and reduce heat conductivity, which would be better for thermoelectric applications. The integration of SWCNT and MXene can provide more phonon scattering, which causes reduced thermal conductivity; however, it also depends on the thickness of the material. Additionally, the various surface termination groups provide more options for modifying MXene, leading to combinations that possess the necessary capabilities. The inherent two-dimensional layered structure makes it possible to regulate properties practically and to assemble several layers. Due to these qualities, there are exciting prospects to adjust the electrical and thermal properties of MXene, which has promise in the field of thermoelectrics.

Herein, a thermoelectric device was fabricated using the bucky paper by combining single-walled carbon nanotubes (SWCNTs) and 2D MXene (Ti₃C₂T_x) sheets. This combination of materials helped to achieve a significantly lower heat conductivity by introducing phonon scattering into the system while simultaneously improving electrical conductivity. We accomplished this by creating a hollow three-dimensional structure that serves as a thermal insulator and by using energy filtering at the MXene/SWCNT interfaces to increase the Seebeck coefficient. The M90C10 bucky paper, composed of 90 wt.% MXene and 10 wt.% SWCNT, achieved a Seebeck coefficient of 50.45 μV/K and a power factor of 3.82 μW/(m⋅K²). A prototype thermoelectric device was fabricated with the same composition, having a Seebeck coefficient of 320.77 μV/K and a maximum output power of 0.053 μW to confirm its promise for high-performance and scalable thermoelectric applications.

Introduction: Waste-to-hydrogen technology requires the involvement of new material development and performance evaluation for Additive Manufacturing (AM). Metal 3D printing is a very good possible alternative and is delivering results visible in the circular economy environment. By using the AM technique, complex operations are avoided when combining the individual components, which is a typical disadvantage in obtaining composite materials; such samples are prepared with only one operation from the starting melt, which is chemically defined. Pyrolysis rotary kiln sealing rings are to be upgraded with several different in microstructure coatings in order to improve the surface performances. The surface topology is aimed to be fine, dense and smooth. Also, the target characteristics are a low friction coefficient and a high hardness value, suggesting enhanced wear resistance. For elevated temperatures, 900 ^oC is selected for cobalt-based superalloy Stellite types with particle reinforcement.

Method: Two possibilities for advanced materials obtainment are proposed with the Directed Energy Deposition Plasma Arc (DED-arc) and Laser Directed Energy Deposition (DED-LB). The shell of the rotary kiln sealing ring is to be made of stainless steel as the base, with the coating overlayed. Selected mixtures in powder form with defined composition are applied. For the DED-arc, commercially available Stellite 6 (Deloro Stellite® 6, GmbH, Germany) and 20 vol% WC particles with a grain size of 63 - 150 µm were employed. For the DED-LB, we employed TRIBALOY^® T-800 (Kennametal Stellite^TM) with 25 vol% TiC and a mesh size of -100/+325 (particle diameter between 45 and 150 µm). After the representative samples were metallurgically bonded with the base stainless steel, the relevant properties were obtained.

Results: Manufactured samples are compared in terms of microstructures and mechanical properties. Analysis of structure: Intermetallic carbides that formed on the cobalt basis make the composite harder and increase the plasticity in a defined direction. The hypoeutectic structures of Stellite 6 + 20%WC consist of dendrite and interdendrite eutectic. It is observed that with an increase in WC volume fraction, the size of the dendrites becomes finer and the amount of eutectic structure is increased. For the TRIBALOY^® T-800 with TiC, we obtained relatively smaller grain sizes. The roughness values for the tested samples with WC were initially Ra=0.8 µm, increasing up to Ra=3.44 µm after the wear test, whereas for the TiC, it was slightly lower. Microhardness testing revealed increased values compared to the base stainless steels. Advanced sensor analysis with Acoustic Emission (AE) and Electrical Contact Resistance (ECR) also showed the properties of the new materials.

Conclusion: Customizable coatings with tailored properties were deposited by DED-arc and DED-LB. From the tests performed, a new technological procedure for obtainment is proposed for novel pyrolysis rotary kiln sealing rings. The microhardness, roughness, microstructure and abrasive wear-resistant response of the metallic composite material were examined in order to characterize the stable multiphase system.

Funding: The author acknowledges support from project BG16RFPR002-1.014-0005.

The cation composition of metal halide perovskites plays a critical role in determining internal charge carrier dynamics and volumetric recombination within the absorber layer. While methylammonium (MA)-based perovskites serve as a foundational baseline, the incorporation of formamidinium (FA) cations has been shown to enhance optoelectronic properties under various environmental conditions [1, 4]. Despite these advancements, the quantitative relationship between specific MA:FA ratios and the resulting carrier survival within the perovskite domain remains a subject of intense research. In this study, the internal generation–recombination balance and its dependence on absorber thickness (d) are investigated using a one-dimensional (1D) finite element method (FEM) framework, strictly validated against champion experimental data obtained from sol–gel-fabricated solar cells [5].

Three representative compositions were analyzed: pure MA (MA100), MA-rich (MA70:FA30), and equimolar MA-FA (MA50:FA50). Experimental characterization reveals distinct performance trends across the compositions. The pure MA baseline achieved a power conversion efficiency (PCE) of 14.4% with an open-circuit voltage (Voc) of 1.040 V. In contrast, the MA-rich (MA70:FA30) composition emerged as the champion, reaching a PCE of 18.6% and a Voc of 1.029 V. The equimolar MA-FA composition resulted in a PCE of 14.1% and a Voc of 0.948 V. These results provide the empirical foundation for a numerical assessment of internal loss mechanisms.

The simulation follows a structured two-stage approach. First, specific volumetric recombination rates are extracted by calibrating the model to match the experimental results at the baseline thickness. Second, a systematic thickness sweep is performed to evaluate the carrier collection efficiency. The spatial distribution of SRH recombination obtained from the FEM simulations enables the extraction of a volume-averaged effective carrier lifetime (tau_eff). Based on this, the carrier diffusion length is calculated as Ld = sqrt(D * tau_eff). These calculated diffusion lengths are directly compared with the absorber thickness (d) to explicitly demonstrate diffusion length-limited (Ld < d) and transport-balanced (Ld >= d) regimes [3,7]. This Ld-d comparison establishes a direct quantitative link between observed performance trends and recombination-dominated transport, providing a robust framework for thickness optimization in mixed-cation perovskite photovoltaics [5, 7].

[1] Tress, W.

Perovskite Solar Cells on the Way to Their Radiative Efficiency Limit – Insights into a
Success Story of High Open-Circuit Voltage and Low Recombination.
Advanced Energy Materials, 2017, 7, 1602358.

[2] Kirchartz, T.; Staub, F.; Rau, U.

Recombination, Collection, and Voltage Losses in Solar Cells.
Physical Review Applied, 2016, 6, 034003.

[3] Kirchartz, T.

Photon Management in Perovskite Solar Cells.
Journal of Physical Chemistry Letters, 2019, 10, 5892–5896.

[4] Chen, J.; Xu, J.; Xiao, L.; Zhang, B.; Dai, S.; Yao, J.

Mixed-Organic-Cation (FA)x(MA)1−xPbI₃ Planar Perovskite Solar Cells with Enhanced Carrier Lifetime and Stability.

ACS Applied Materials & Interfaces, 2017, 9, 2449–2458.

[5] Gökdemir Choi, F. P.; Güneş, S. et al.

A Novel Interface Layer for Inverted Perovskite Solar Cells Fabricated in Ambient Air under
High Humidity Conditions.
Solar Energy, 2020, 209, 400–407.

[6] Berhe, T. A.; Su, W.-N.; Chen, C.-H.; et al.

Organometal Halide Perovskite Solar Cells: Degradation and Stability.
Energy & Environmental Science, 2016, 9, 323–356.

[7] Stranks, S. D.; Snaith, H. J.

Metal-Halide Perovskites for Photovoltaic and Light-Emitting Devices.
Nature Nanotechnology, 2015, 10, 391–40

Introduction

The unprecedented rise in atmospheric carbon dioxide (CO₂) concentration represents one of the most critical challenges for modern energy systems, directly impacting climate stability and energy sustainability [1, 2]. Carbon capture and storage (CCS) technologies are therefore indispensable for enabling low-carbon energy transitions. Among emerging solutions, porous carbons derived from biomass have attracted increasing attention due to their low environmental footprint, scalability, and structural tunability [3]. Grape seeds, a major waste stream of the wine industry, constitute an abundant lignocellulosic resource with untapped potential for advanced energy and environmental applications [4]. Despite growing interest in biomass-derived carbons, a fundamental understanding of how activation strategies govern pore architecture and CO₂ adsorption efficiency remains insufficient.

Methods

In this work, grape seed-derived activated carbons were synthesized via chemical and physical activation routes at temperatures between 600 and 800 °C to systematically evaluate structure–performance relationships. The materials were comprehensively characterized using XRD, Raman spectroscopy, XRF, SEM, and N₂ adsorption–desorption analyses to determine their crystallinity, chemical purity, morphology, and pore structure. To bridge macroscopic performance with microscopic mechanisms, Grand Canonical Monte Carlo (GCMC) simulations were employed to investigate CO₂ adsorption behavior [5], interaction energies, and isosteric heats of adsorption at the molecular level.

Results

Chemical activation yielded a highly developed porous carbon (AC-GC-C-800) with an exceptional specific surface area of 1968 m² g⁻¹ and a total pore volume of 1.22 cm³ g⁻¹. In contrast, physically activated carbons exhibited progressively reduced porosity and larger particle sizes with decreasing activation temperature. Structural analyses revealed that AC-GC-C-800 possessed the highest degree of structural disorder (I_D/I_G = 0.75), which strongly correlated with enhanced microporosity and superior CO₂ uptake. As a result, AC-GC-C-800 achieved a CO₂ adsorption capacity of 6.5 mmol g⁻¹ at 273 K and 4.8 mmol g⁻¹ at 298 K under 1 bar, outperforming physically activated counterparts by up to ~40%. Elemental analysis confirmed that KOH activation effectively removed inorganic impurities, resulting in a carbon purity of 92.5 wt%. GCMC simulations demonstrated that while surface area dominates adsorption at elevated pressures, CO₂ capture under low-pressure, post-combustion conditions is governed by the presence of narrowly distributed ultra-micropores [6, 7]. Simulation snapshots and energy analyses clearly showed stronger host–guest interactions in chemically activated carbons.

Conclusions

This study reveals that precise control of pore geometry, rather than surface area alone, is the decisive factor governing CO₂ capture efficiency in biomass-derived carbons. By combining advanced characterization with molecular-level simulations, this work provides a mechanistic framework for designing high-performance, sustainable adsorbents for CCS applications. The results highlight grape seed waste as a viable feedstock for advanced energy materials and contribute to the rational development of carbon capture technologies aligned with circular economy and low-carbon energy strategies

Acknowledgments

This research was funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (grant no. AP19679878—Conversion of plant biomass waste into microporous activated carbons to successfully capture and separate CO₂, N₂ and CH₄.)

References

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2. D'Alessandro, D.M., B. Smit, and J.R. Long, Carbon Dioxide Capture: Prospects for New Materials. Angewandte Chemie International Edition, 2010. 49(35): p. 6058-6082.
3. Priya, D.S., L.J. Kennedy, and G.T. Anand, Emerging trends in biomass-derived porous carbon materials for energy storage application: A critical review. Materials Today Sustainability, 2023. 21: p. 100320.
4. Montoya, V.H. and A. Bonilla-Petriciolet, Lignocellulosic precursors used in the synthesis of activated carbon: characterization techniques and applications in the wastewater treatment. 2012: BoD–Books on Demand.
5. D. Frenkel, B.S., Understanding Molecular Simulation: From Algorithms to Applications. Elsevier, 2023. San Diego: Academic Press: p. 443.
6. Dziejarski, B., et al., Tailoring highly surface and microporous activated carbons (ACs) from biomass via KOH, K₂C₂O₄ and KOH/K2C2O4 activation for efficient CO₂ capture and CO2/N2 selectivity: characterization, experimental and molecular simulation insights. Chemical Engineering Journal, 2025. 524: p. 169677.
7. Tiyawate, A., et al., Combined experimental and grand canonical Monte Carlo simulation study of CO2 capture in nitrogen and sulfur co-doped biochar derived from biowaste: Cost analysis, kinetics, and equilibrium. Journal of Environmental Chemical Engineering, 2024. 12(5): p. 113991.

Sustainable building design increasingly relies on passive solar thermal systems to reduce the carbon footprint of space heating. Among these technologies, building-integrated solar air collectors mounted on facades or roofs offer a cost-effective solution for fresh air preheating. However, the performance of natural convection collectors is inherently limited by the delicate balance between buoyancy-driven flow and heat loss through the glazing. This study presents a detailed three-dimensional numerical investigation into the thermal behavior of a passive solar air collector, comparing conventional glass covers with monolithic silica aerogel as a transparent insulation material.

The numerical model was developed within the Ansys Fluent environment, focusing on the thermosiphon effect, where the flow is entirely driven by buoyancy forces rather than external mechanical power. To accurately capture the physics of natural convection, the Boussinesq approximation or ideal gas density variations were employed in conjunction with the gravitational vector. A multi-band radiation modeling approach was implemented to decouple the incoming short-wave solar radiation from the long-wave thermal radiation emitted by the absorber. This allowed for a realistic assessment of the "greenhouse effect" and the radiative shielding provided by the aerogel layer in a vertical or inclined mounting configuration.

The findings reveal that monolithic aerogel acts as a transformative component for passive systems. In natural convection collectors, flow velocities are typically low, which usually leads to high stagnation temperatures and increased top heat losses in glass-covered units. The integration of aerogel, with its exceptionally low thermal conductivity and high infrared absorption, effectively suppresses these losses. Numerical results indicate that the aerogel-integrated collector maintains a significantly higher thermal equilibrium, leading to improved absorber surface temperatures and enhanced air delivery temperatures into the building interior. While the porous structure of the aerogel introduces a minor penalty in solar transmittance, the resultant enhancement in the stack effect—driven by higher internal temperatures—compensates for this by maintaining a stable and warm airflow. This research demonstrates that aerogel-based glazing is a superior alternative for the next generation of building-integrated passive solar systems, where thermal retention is the primary driver of overall seasonal efficiency.

Direct hydrazine fuel cells (DHFCs) have attracted significant interest as a promising method for sustainable hydrogen production, as they can overcome the slow oxygen evolution rate that limits conventional water splitting. The practical deployment of DHFCs is strongly dependent on the availability of cost-effective and efficient anode electrocatalysts for the hydrazine oxidation reaction (HzOR). The current study proposes a straightforward, scalable, and ecologically sustainable approach to the synthesis of non-noble metal electrocatalysts derived from sustainable biomass resources. The synthesis of nitrogen-doped carbon (N–C) was achieved through a hydrothermal carbonisation (HTC) process, utilising birchwood chips. This was followed by activation and nitrogen incorporation, yielding a porous, conductive carbon framework. Subsequently, iron (Fe) and manganese–iron (MnFe) were introduced as active components. The morphology, structure, and elemental composition of the MnFe, MnFe/N–C, and Fe/N–C catalysts were characterised by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS). The catalytic activity of the catalysts for HzOR was evaluated in an alkaline medium by performing cyclic voltammetry (CV).

Electrochemical investigations have demonstrated that the MnFe/N–C catalyst demonstrates a significantly enhanced HzOR activity, exhibiting a lower onset potential and a substantially higher current density in comparison with both Fe/N–C and MnFe counterparts. The enhanced electrocatalytic performance of MnFe/N–C is attributable to a combination of factors, including the presence of numerous exposed active sites, the optimised mass transport within the porous nitrogen-doped carbon matrix, and the robust synergistic interactions between Mn, Fe, and N–C. The results of this study identify MnFe/N–C as a highly promising anode material for DHFCs. This work offers a viable, cost-effective, and sustainable approach to the design of efficient electrocatalysts that do not utilise noble metals. It provides significant insights into the development of next-generation hydrazine-based energy conversion and hydrogen production technologies.

Acknowledgment

This research was funded by a grant (No. P-ST-23-310) from the Research Council of Lithuania.

Flexible perovskite solar cells (PSCs) combine high efficiency with sustainability, making them a hot spot in green energy and a promising candidate for large-scale industrial production ^[1][2]. While Al foil offers excellent moisture and oxygen barrier properties, high thermal tolerance, and mechanical robustness, it’s the key point for the industrial roll-to-roll (R2R) production of lightweight, stable, and low-cost photovoltaic modules ^[3]. However, its surface roughness and interfacial incompatibility with perovskite layers cause challenges to device performance and upscaling.

This work addresses these challenges through a multi-faceted approach combining substrate engineering, interfacial modification, and scalable deposition techniques. Within the framework of the Horizon Europe Luminosity project, a successfully implemented barrier/ITO stack on Al foil, which serves as a smooth, conductive, and chemically compatible base for perovskite deposition, through the optimization of self-assembled monolayers (SAMs, e.g., MeO-4PACz) and interfacial passivation (e.g., PEACl), improved charge extraction and reduced hysteresis. The best-performing flexible PSCs on Al/barrier/ITO substrates with a semitransparent stack achieve a power conversion efficiency (PCE) of 14.64%, with low hysteresis and operational stability. Comparative studies on semitransparent Glass/ITO references with PCE up to 17.59% demonstrate the ongoing optimization pathway for Al-substrate devices. Furthermore, we report progress in laser patterning for monolithic module interconnection, a key step in R2R manufacturing.

This work demonstrates the feasibility of aluminum-substrate PSCs and highlights the crucial role of interface control in improving efficiency and stability. By combining material innovation with industrially relevant processing routes, we provide a viable path to commercializing high-performance, durable, and sustainable perovskite photovoltaic modules.

[1] S. Aftab, M.Z. Iqbal, S. Hussain, H.H. Hegazy, M.A. Saeed, Nano Energy (2023), 108249.

[2] L. Yang, J. Feng, Z. Liu, Y. Duan, S. Zhan, S. Yang, K. He, Y. Li, Y. Zhou, N. Yuan, Adv. Mater. 34 (2022) 2201681.

[3] A. Kumar, S. Rani, D. S. Ghosh, Sol. Energy Mater. Sol. Cells. 268 (2024) 112737.

Photocatalytic methanol reforming offers a low-temperature route to hydrogen production, yet controlling product selectivity remains a key challenge. Here, we evaluate Cs₂RuX₆ (X = Cl, Br) double-perovskite photocatalysts for methanol reforming under mild conditions (2 mg catalyst, 25 °C, 1.0 bar Ar, 130 mW·cm⁻² irradiation, 3 h), tracking time-resolved gas evolution to elucidate substrate-loading effects and halide-dependent behaviour. Methanol addition markedly enhances H₂ generation compared with methanol-free conditions for both catalysts. Cs₂RuCl₆ shows the highest H₂ productivity at intermediate methanol loading, reaching ~10 mmol·g_cat⁻¹ after 3 h at ~39.6 mmol methanol, while Cs₂RuBr₆ attains ~7–8 mmol·g_cat⁻¹ under the same loading. Increasing methanol to higher levels (e.g., ~98.9 mmol) reduces H₂ output for both materials, indicating an optimum substrate range rather than a monotonic dependence.

O₂ evolution exhibits a contrasting trend: the presence of methanol generally suppresses O₂ formation, most clearly for Cs₂RuBr₆, consistent with competitive consumption of oxidative equivalents in the reforming network. In parallel, carbon-containing gaseous products are co-generated, revealing strong selectivity changes with methanol loading and catalyst halide. CH₄ formation increases with time and is maximised at intermediate methanol loadings (e.g., ~8 mmol · g_cat⁻¹ for Cs₂RuCl₆ at ~39.6 mmol after 3 h; lower maxima for Cs₂RuBr₆). CO production is also favoured at moderate methanol amounts (up to ~3–4 mmol · g_cat⁻¹ for Cs₂RuCl₆ around ~21.9 mmol), whereas higher methanol loading diminishes CO yields. Notably, C₂H₄ emerges as a dominant carbon product on both catalysts, reaching ~350 μmol · g_cat⁻¹ for Cs₂RuCl₆ and ~270 μmol · g_cat⁻¹ for Cs₂RuBr₆ at ~39.6 mmol methanol after 3 h, highlighting a pronounced substrate-dependent shift towards C–C containing products.

Overall, these results demonstrate that Cs₂RuX₆ perovskites enable methanol reforming at ambient temperature with substantial hydrogen evolution and tunable multi-gas selectivity. The combined halide comparison and substrate-loading optimisation provide practical guidelines for balancing H₂ productivity against carbonaceous by-products in perovskite-based reforming systems.

Looking ahead, the demonstrated loading-dependent trade-off between hydrogen productivity and carbonaceous by-product formation offers a clear lever for process tuning. By identifying an optimum methanol range and highlighting distinct selectivity patterns for Cl versus Br, this study sets a baseline for rational catalyst and reactor optimisation. Future work will couple in situ spectroscopy with mass-balance analysis to map reaction pathways and to suppress undesired products, enabling more efficient solar-to-chemical conversion using perovskite reforming platforms under ambient conditions relevant to deployment.

Introduction:

Thin-film solar cells based on CdTe, CIGS, and perovskites have achieved high efficiencies, but their large-scale industrialization remains limited by toxicity issues related to cadmium or lead and by the scarcity of critical elements such as indium, gallium, and tellurium. In this context, tin monosulfide (SnS) has emerged as a promising absorber material because of the abundance and non-toxicity of its constituents, its direct band gap close to 1.3 eV, and its high absorption coefficient, which makes it suitable for thin-layer solar cells. However, the conventional SnS/CdS architecture still suffers from important limitations, including parasitic absorption in the blue–UV region by the CdS layer, unfavorable band alignment at the interface, enhanced recombination, and consequent degradation of the open-circuit voltage (Voc), short-circuit current density (Jsc), and fill factor (FF).

Methods:

To address these limitations, this work proposes a detailed numerical study of cadmium-free SnS solar cells using SCAPS-1D. The study first considers replacing the CdS buffer layer with alternative Cd-free materials, particularly zinc selenide (ZnSe) and molybdenum disulfide (MoS₂), in order to optimize the conduction band offset at the interface with the absorber and reduce recombination losses. In parallel, the effect of introducing back surface field (BSF) or hole transport layers (HTL), such as NiO and Cu₂O, between the SnS absorber and the rear metal contact is analyzed, with the aim of blocking electrons, facilitating selective hole extraction, and lowering rear–interface recombination. Different combinations of buffer and BSF/HTL layers are systematically examined together with their physical and electrical parameters, including thickness, doping, band gap, and defect density.

Results:

The numerical analysis is intended to identify device architectures offering the best compromise between band alignment, recombination reduction, and simultaneous improvement of Voc, Jsc, and FF. The comparison focuses on Cd-free configurations based on ZnSe or MoS₂ buffer layers combined with NiO or Cu₂O as BSF/HTL layers, relative to the reference SnS/CdS structure.

Conclusions:

This study aims to identify a truly Cd-free SnS solar-cell structure with improved conversion efficiency compared with the conventional SnS/CdS configuration. It also seeks to provide practical guidance for the experimental implementation of environmentally friendly and efficient SnS-based solar cells.