Bridging materials and devices: Selenium-driven bandgap and transport tuning in CdTe1−xSex solar cells

Abstract

Thin films of CdTe 1-x Se x were prepared and studied across the full selenium range to understand how composition shapes usefulness of the films as photovoltaic absorber layers. Using thermal evaporation to deposit ∼0.75 μm films, the structure evolves from CdTe-dominant cubic features to Se-rich mixed cubic–hexagonal phases as the selenium content x increases. This structure variation is accompanied by changes in grain texture and crystallinity seen by X-ray diffraction (XRD) and scanning electron microscope (SEM). Optical measurements show that moderate selenium incorporation narrows the band gap and raises the refractive index, which boost absorption without introducing excessive loss channels. Electrical tests indicate that this moderate selenium range of composition improves carrier concentration, mobility, and resistivity, supporting better charge transport. Among the alloys, CdTe 0.6 Se 0.4 achieves the best balance of structure, optics, and transport, and when integrated into n-CdS/p-CdTe and n-CdS/p-CdTe/CdTe 0.6 Se 0.4 devices, it delivers power conversion efficiencies of 17.62% and 20.25% under AM 1.5G, respectively. These findings demonstrate that the optimal selenium concentration in CdTe₁₋ₓSeₓ thin films is around x = 0.4, and the CdTe₀.₆Se₀.₄ composition stands out as a promising candidate for high-efficiency solar cell applications, which then offers a balance between structural stability, optical absorption, and electrical conductivity.