Influence of Rapid Thermal Annealing Temperature on Cu ₂ BaSnSe ₄ (CBTSe) Thin Films Prepared by Hybrid Spin Coating and Thermal Evaporation

Herein, Cu 2 BaSnSe 4 (CBTSe) thin films are fabricated via a two‐stage process combining spin coating and thermal evaporation, followed by rapid thermal annealing at selenization temperatures of 525, 550, and 575 °C. Cu–Ba–Sn precursor films are prepared by spin coating, and a Se‐cap layer is deposited by thermal evaporation. Structural, optical, and electrical properties are investigated using X‐ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), energy‐dispersive X‐ray spectroscopy, photoluminescence (PL), and Van der Pauw measurements. XRD confirms the formation of the hexagonal CBTSe phase, with the largest crystallite size (≈78 nm) at 575 °C. Minor SnSe and Ba–Sn–O secondary phases are also detected. SEM reveals dense polycrystalline structures with grain growth at higher temperatures. Surface morphology analysis shows that roughness increases from 34.90 nm (525 °C) to 84.30 nm (575 °C), consistent with SEM observations and literature trends indicating grain coarsening at higher annealing temperatures. PL spectra exhibit emission near 1.91–1.93 eV. All films display p‐type conductivity with carrier concentrations around 10 16 cm −3 . Among the investigated samples, the film selenized at 575 °C demonstrates superior crystallinity, enhances optical absorption, increases roughness, and improves electrical performance, making it a promising candidate for high‐efficiency solar cell applications.