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S. AMEEN1, M. SAJID1, K. ALI1,*
Single-junction solar cells are fundamentally limited by the Shockley-Queisser efficiency ceiling due to incomplete utilization of the solar spectrum. In this work, we propose and numerically optimize a monolithic tandem solar cell based entirely on tungsten diselenide (WSe₂) using SCAPS-1D simulation software. The top cell employs germanium-incorporated WSe₂ (WSe₂:Ge) as the wide-bandgap absorber (Eg ≈ 1.6 eV), while the bottom cell uses pristine WSe₂ as the narrow-bandgap absorber (Eg ≈ 1.0 eV). A Cu₂O hole transport layer and ZnO electron transport layer are used to facilitate charge extraction. Systematic optimization of absorber layer thicknesses yields current-matched operation (Jsc = 18.53 mA/cm²) at top and bottom cell thicknesses of 1.08 μm and 1.62 μm, respectively. The optimized monolithic tandem structure achieves an open-circuit voltage (Voc) of 0.743 V, short-circuit current density (Jsc) of 43.18 mA/cm², fill factor (FF) of 84.82%, and a power conversion efficiency (PCE) of 21.94% under standard AM1.5G illumination. This efficiency surpasses previously reported single-junction WSe₂ solar cells and demonstrates the potential of same-material monolithic tandem architectures using earth-abundant, non-toxic transition metal dichalcogenides. The results provide a theoretical foundation for experimental realization of high-efficiency WSe₂-based tandem photovoltaics.
WSe2/WS2, Bandgap Engineering, Cu₂ZnSn₀.₈Ge₀.₂S₄ (CZTGSe), Tandem Solar cell, Thin film solar cells, SCAPS-1D.
S. AMEEN, M. SAJID, K. ALI, Numerical optimization of a monolithic WSe₂/WS₂ tandem solar cell: achieving 21.94% efficiency via bandgap engineering in SCAPS-1D, Optoelectronics and Advanced Materials - Rapid Communications, 20, 7-8, July-August 2026, pp.319-328 (2026).
Submitted at: July 6, 2025
Accepted at: Aug. 3, 2026
Optoelectronics and Advanced Materials - Rapid Communications
(2025): Impact Factor = 0.5 - Journal Citation Reports (Clarivate Analytics, 2026)
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