Investigation of 2D MoTe2 for Thin-Film CdTe Tandem Solar Cells

Solar cells have emerged as an important technology in the transition toward renewable energy, driven by the need for sustainable and efficient energy sources. Thin-film solar cells, in particular, offer unique advantages, such as reduced material usage, mechanical flexibility, and potential for integration into diverse applications. Preliminary calculations indicate that tandem device architectures with CdS/CdTe top-cell and 2D- MoTe₂ (Eg = 1.1 eV) bottom cell can achieve tandem device efficiency of as high as 55%. A comparative analysis with traditional thin-film materials such as Sb2Se3 (Eg = 1.17 eV) and CIGS (Eg = 1.1 eV), as bottom cell absorbers will also be presented. Within the category, 2D Transition Metal Dichalcogenides (TMDs) such as 2D-MoTe₂ have showed significant attention due to their exceptional optical and electronic properties. 2D-MoTe₂, with its narrow direct bandgap (1.10 eV), is especially well-suited for solar cell applications, enabling effective light absorption across a broad spectrum. In this study, we investigate a superstrate ITO/MoTe₂/metal thin-film single-junction solar cell, utilizing 2H-MoTe₂ as the absorber layer.
Simulations of the ITO/MoTe₂/metal device using SCAPS-1D (Solar Cell Capacitance Simulator) indicated a power conversion efficiency (PCE) of ~ 20%, showcasing the potential of this device with an open-circuit (V_OC) of 0.83V, short-circuit current (J_SC) of 28.75 mA/cm² and a fill factor (FF) of 86.06%. To bridge the gap between simulation and experimental validation, commercially available ITO/MoTe₂ substrates, consisting of few-layered MoTe₂ on ITO glass, were procured from 2D Semiconductors. As the initial step in experimental work, UV-Visible spectroscopy was performed to determine the optical properties of the MoTe₂ film, revealing a bandgap of 0.98 eV as derived from the Tauc plot. X-ray diffraction (XRD) analysis displayed characteristic peaks at 12.46°, 25.48°, 38.34°, and 52.44°, corresponding to the (002), (004), (006), and (008) planes of 2H-MoTe₂, confirming the phase purity of the material. These results were further validated by Raman spectroscopy, which showed Raman-active modes related to the in-plane modes and out-of-plane modes for E_1g (118 cm^-1), A_1g (173 cm^-1), and B¹_2g (290 cm^-1), and bulk-inactive mode at E¹_2g (234 cm^-1), indicative of the crystalline quality of the 2H-MoTe₂ structure.
The thickness of the 2H-MoTe₂ layer will be measured using Ellipsometry and Filmetrics, ensuring precise control over the film thickness, which is crucial for optimizing light absorption and charge transport. Photoluminescence (PL) measurements will be conducted to further analyze the optical properties and excitonic behavior of the 2H-MoTe₂ film. High-resolution Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) will provide insights into the microstructural properties and morphology of the MoTe₂ layer, verifying its uniformity and quality. Additionally, Energy-Dispersive X-ray spectroscopy (EDX) will be conducted to analyze the elemental composition and uniformity of the 2H-MoTe₂ film, further verifying the material's stoichiometry.
Following the confirmation of 2H-MoTe₂ as the absorber, we will proceed with the fabrication of the single-junction ITO/MoTe₂/metal solar cell, using a thermal evaporator to deposit gold contacts. The device performance will be characterized using Current-Voltage (IV) measurements and External Quantum Efficiency (EQE) analysis to evaluate its photovoltaic properties under standard testing conditions. This comprehensive study aims to advance the understanding of 2D-MoTe₂-based solar cells and optimize their design for improved efficiency, contributing to the growing field of 2D material-based photovoltaics.