A comprehensive numerical modeling investigation has demonstrated that an emerging eco-friendly quaternary chalcogenide semiconductor, silver barium titanium selenide, possesses strong potential for dual-function energy harvesting and light sensing. Using the one-dimensional Solar Cell Capacitance Simulator, researchers examined the theoretical optoelectronic characteristics of silver barium titanium selenide, abbreviated as ABTSe, across two distinct heterojunction architectures. Under optimized AM 1.5G simulated solar illumination at an incident intensity of 1000 watts per square meter, a baseline zinc selenide and ABTSe heterostructure achieved a power-conversion efficiency of 23.16 percent. By incorporating a thin tungsten diselenide back-surface-field layer behind the absorber, the simulated power-conversion efficiency surged to 31.17 percent. Simultaneously, the simulated three-layer architecture exhibited exceptional light-detection capabilities, demonstrating an extraordinary peak detectivity of 44.5 × 10¹⁵ Jones at a near-infrared wavelength of 980 nanometers and a maximum responsivity of 0.69 amperes per watt at 956 nanometers, providing a theoretical foundation for experimental development.

The study addresses the critical technological push for non-toxic, earth-abundant materials capable of bypassing the physical and economic limitations that burden established photovoltaic and photodetector platforms. Commercially dominant silicon solar cells deliver laboratory efficiencies slightly exceeding 27 percent, but their high melting point demands complex, energy-intensive fabrication processes. Thin-film alternatives such as cadmium telluride have surpassed 23 percent laboratory efficiency, and copper indium gallium diselenide devices have reached 23.6 percent, yet they depend on hazardous cadmium or scarce reserves of indium, gallium, and tellurium. Metal-halide perovskites have demonstrated rapid efficiency increases from 3.8 percent to roughly 27 percent, but they suffer from severe operational instability and environmental concerns surrounding lead toxicity. Earth-abundant copper zinc tin sulfur selenide kesterites offer a non-toxic profile, yet their practical power-conversion efficiency remains stalled at 14.9 percent against a theoretical ceiling of 31 percent due to open-circuit voltage deficits driven by copper-zinc antisite defects.

Photodetector technologies face analogous tradeoffs between material toxicity, structural stability, and spectral sensitivity across critical industrial, optical, and environmental monitoring wavelengths. Conventional photodetectors based on materials such as lead sulfide paired with titanium trisulfide, methylammonium lead iodide, cesium lead iodide, and molybdenum disulfide on silicon typically exhibit detectivities ranging from 7.5 × 10¹⁰ to 3.9 × 10¹³ Jones, accompanied by responsivities spanning 0.3 to 0.6 amperes per watt. Although advanced engineered architectures—including silver nanoparticle-enhanced tungsten-doped zinc oxide on silicon, cadmium germanium phosphide devices, and interface-engineered graphene heterostructures—demonstrate enhanced broadband and infrared responses, identifying sustainable compounds with inherent near-infrared sensitivity remains an active scientific priority. Computational screening combining unsupervised machine learning with density functional theory by Wang and colleagues previously highlighted the quaternary I₂–II–IV–VI₄ semiconductor ABTSe as an exceptional candidate, exhibiting an optimal bandgap of 1.18 electron-volts, strong visible absorption, and robust thermal stability under ambient conditions modeled via ab initio molecular dynamics.

Crucially, the chemical substitution of monovalent silver and divalent barium into the crystal lattice distinguishes ABTSe from troublesome kesterite absorbers by suppressing the formation of harmful antisite defect complexes. Because silver and barium possess substantial differences in ionic radii and chemical properties compared to copper and zinc, deep-level traps that traditionally degrade open-circuit voltage are significantly reduced. Prior numerical modeling of ABTSe explored solar architectures using alkaline earth metal chalcogenide buffers, but those earlier models did not evaluate back-surface-field engineering, interfacial band alignments, or photodetection performance. To address these open questions, the current investigation evaluated a multi-layered photonic structure configured as nickel anode, p⁺-type tungsten diselenide back-surface-field layer, p-type ABTSe absorber layer, n-type zinc selenide window layer, and titanium cathode. Zinc selenide provides a wide bandgap of 2.7 electron-volts, allowing more than 80 percent of incident photons to reach the absorber while serving as an effective, non-toxic alternative to cadmium sulfide.

The simulation framework was executed using SCAPS-1D software, which solves the coupled Poisson equation, electron and hole continuity equations, and drift-diffusion equations subject to defined physical boundary conditions. The simulation assumed thermal velocities of 10⁷ centimeters per second for both charge carriers, ideal series and shunt resistances, and incorporated discrete interface defects resulting from lattice mismatch at each heterointerface. Electronic band alignments were quantitatively evaluated according to Anderson’s electron-affinity rule. For the front zinc selenide and ABTSe junction, conduction band minima of 4.09 and 4.10 electron-volts yielded a near-ideal spike-like conduction band offset of 0.01 electron-volts, facilitating smooth electron extraction, while a large valence band offset of 1.51 electron-volts blocked hole leakage into the front window. At the rear ABTSe and tungsten diselenide boundary, conduction and valence band offsets of 0.48 and 0.04 electron-volts formed an electron-reflecting barrier and an unobstructed hole-transport channel.

A direct comparison between the dual-layer zinc selenide and ABTSe heterojunction and the three-layer architecture containing the tungsten diselenide back-surface-field layer revealed the decisive mechanism underlying the efficiency surge. While short-circuit current density remained virtually unaltered—shifting marginally from 38.82 to 38.85 milliamperes per square centimeter—the open-circuit voltage increased dramatically from 0.71 volts to 1.00 volt upon adding the tungsten diselenide layer. Mott-Schottky capacitance-voltage analysis confirmed that the built-in potential rose from 0.65 volts in the two-layer device to an aggregate of 1.31 volts across the dual interfaces of the three-layer cell. This internal field pushes photogenerated minority electrons away from the defect-rich rear interface back toward the primary depletion region, sharply diminishing reverse saturation current density. Although an increase in series resistance reduced the fill factor from 84.55 to 80.17 percent, the elevated voltage propelled overall efficiency beyond 31 percent.

Parametric sweeps systematically optimized the individual structural dimensions, doping concentrations, and defect thresholds of the constituent semiconductor layers. Expanding the ABTSe absorber thickness from 0.3 to 1.1 micrometers boosted optical absorption, driving short-circuit current density upward from 34.30 to 39.95 milliamperes per square centimeter, though increased bulk recombination caused open-circuit voltage to decline from 1.04 to 0.98 volts; an intermediate thickness of 0.7 micrometers was established as the optimum. Raising the acceptor concentration beyond 10¹⁶ per cubic centimeter triggered defect-assisted Shockley-Read-Hall recombination that shortened carrier lifetimes, lowering efficiency from 31.22 to 28.92 percent. Bulk defect concentrations in the absorber proved particularly influential, as increasing defect density from 10¹² to 10¹⁶ per cubic centimeter reduced the open-circuit voltage from 1.16 to 0.69 volts and caused efficiency to fall from 37.79 to 20.67 percent, cementing an optimal design density of 10¹⁴ per cubic centimeter.

In contrast to the highly sensitive absorber layer, the zinc selenide window and tungsten diselenide back-surface-field layers exhibited wide operational tolerances during parametric probing. Varying zinc selenide thickness between 0.05 and 0.25 micrometers, donor doping from 10¹⁶ to 10²⁰ per cubic centimeter, and defect densities from 10¹² to 10¹⁶ per cubic centimeter produced virtually no degradation in photovoltaic metrics because high carrier mobilities and diffusion lengths allowed electrons to reach the cathode before recombining. Similarly, varying tungsten diselenide thickness between 0.1 and 0.5 micrometers, along with broad variations in acceptor doping and defect levels, sustained a stable power-conversion efficiency of 31.17 percent. Interface defect concentrations at both heterointerfaces were also assessed, demonstrating that rising defect densities from 10¹⁰ to 10¹⁴ per square centimeter introduced localized mid-gap recombination states that diminished open-circuit voltage and overall power conversion, identifying 10¹⁰ per square centimeter as the ideal interface fabrication target.

Environmental temperature analysis between 275 and 400 Kelvin highlighted thermal vulnerabilities typical of narrow-bandgap semiconductor devices. As operating temperature increased, thermal excitation and bandgap narrowing caused the intrinsic carrier concentration to multiply, precipitating an exponential surge in reverse saturation current that degraded open-circuit voltage from 1.02 to 0.90 volts. Concurrently, enhanced lattice vibrations and phonon scattering impaired carrier mobility, lowering the fill factor from 81.68 to 74.07 percent and reducing simulated efficiency from 32.49 to 25.92 percent, while short-circuit current density remained essentially flat. Metal contact optimization indicated that the front cathode required a low work function to preserve carrier collection, identifying titanium at 3.84 electron-volts as superior to aluminum or manganese, whereas the rear contact performed reliably across various conductive metals, allowing the selection of economical nickel with a work function of 5.20 electron-volts to establish an ohmic contact.

Evaluation of the architecture as a self-powered photodetector revealed impressive sensitivity originating from high quantum efficiency and reduced dark current. Calculated under the standard shot-noise-limited framework, spectral responsivity rose steadily with wavelength from 0.24 amperes per watt at 300 nanometers to a sharp peak of 0.69 amperes per watt at 956 nanometers before collapsing beyond 1040 nanometers where incident photon energy drops below the 1.18 electron-volt bandgap. Specific detectivity demonstrated a substantial enhancement in the presence of the tungsten diselenide layer, climbing from 1.6 × 10¹⁴ Jones in the unpassivated structure to 44.5 × 10¹⁵ Jones at 980 nanometers. Because the single-junction Shockley-Queisser theoretical limit for an idealized 1.18 electron-volt absorber under AM 1.5G irradiation is approximately 32.6 percent, the predicted 31.17 percent photovoltaic efficiency represents an upper-bound performance estimate that neglects top-grid shadowing, optical reflection, parasitic contact resistances, and non-radiative trap networks encountered during physical device fabrication.

Subject of Research: Numerical modeling of Ag2BaTiSe4 photovoltaic and photodetector device architectures

Article Title: Numerical investigation of photovoltaic and photodetector performances of Ag2BaTiSe4-based photonic devices

Article References: Mondal, B. K., Rifat, M. T. H., Paramanik, M. M. R., & Hossain, J. (2026). Numerical investigation of photovoltaic and photodetector performances of Ag2BaTiSe4-based photonic devices. Discover Electronics, 3(1), Article 129. https://doi.org/10.1007/s44291-026-00282-z

Image Credits: AI Generated

DOI: 10.1007/s44291-026-00282-z

Keywords: Ag2BaTiSe4, photovoltaics, photodetectors, SCAPS-1D, thin-film solar cells, heterojunction, chalcogenides, optoelectronics, Numerical, investigation, photovoltaic, photodetector