Development of Chalcogenide-Based Graded Bandgap Thin Film Structure of 𝒁𝒏𝑶𝑺/𝑺𝒃𝟐𝑺𝟑/𝑺𝒃𝟐𝑺𝒆𝟑 by Chemical bath deposition technique for Solar Cell Application

A tri-layer ZnOS/Sb2S3/Sb2Se3 thin-film structure was successfully fabricated for potential application in heterojunction graded bandgap solar cells. The films were deposited using chemical bath deposition (CBD) technique, which provided a simple and cost-effective fabrication route. The fabricated ZnOS/Sb2S3/Sb2Se3 thin-film structure demonstrated good stability and excellent photon absorption capability over a wide spectral range. Optical analysis revealed high absorbance values in the UV region with an absorbance value of over 80%. X-ray diffraction (XRD) studies revealed that the deposited tri-layer films were amorphous in nature and remained amorphous after annealing. The film material exhibited both direct and indirect bandgap energies. Graded direct bandgap energy obtained for the ZnOS/Sb2S3/Sb2Se3 tri-layer structure ranged from 1.42 - 3.77 eV for as-grown and 1.67 – 3.48 eV for annealed film materials and the indirect graded bandgap energy for as-grown and annealed films were estimated to be 0.67 eV – 3.84 eV and 1.04 eV – 3.74 eV respectively. The elemental composition was confirmed by X-ray fluorescence (XRF) and energy dispersive X-ray (EDX) analyses. Atomic force microscopy (AFM) analysis showed that the root mean square (RMS) surface roughness of the ZnOS/Sb2S3/Sb2Se3 films decreased consistently with increasing annealing temperature. Overall, the graded bandgap characteristic of the ZnOS/Sb2S3/Sb2Se3 thin-film structure makes it a promising candidate for high-efficiency solar cell applications, as it supports effective absorption of photons across a broad range of the solar spectrum.