Based on findings originally published as “Optical Properties of Cadmium Sulphide (CdS) Thin Films Spin-Coated on Glass Substrates,” Jordan Journal of Physics, Vol. 14, No. 1 (2021), pp. 49–58.

Nigerian physics researcher Aregbesola Ayodimeji Emmanuel advanced research into cadmium sulphide (CdS) thin films, a long-established semiconductor material prized for its wide, direct band gap and its role as a “window layer” that lets sunlight through to the active layers of a solar cell. The study concentrated on establishing foundational optical and structural benchmarks for the material, the groundwork on which advances in solar-cell design are typically built.

Ayodimeji, a graduate of the Department of Physics at the University of Ilorin, has contributed to research refining one of the most established materials in thin-film photovoltaics using low-cost, scalable fabrication methods. Working with his advisor, Prof. Osanyinlusi Oluwatoyin, he examined how annealing temperature shapes the optical and structural behaviour of CdS films deposited by spin coating — a technique valued for its low cost, ease of composition control, and ability to produce uniform films without a vacuum chamber.

In the study, which has been published in the Jordan Journal of Physics, Ayodimeji and Oluwatoyin prepared CdS films from cadmium acetate and thiourea and annealed them in air at 200, 300, and 400°C, comparing each against an unannealed control. The work showed that optical transmittance across the visible spectrum rose steadily with annealing temperature, climbing from about 76 percent in the unannealed film to 87 percent at 400°C — a property closely tied to the performance requirements of optoelectronic devices, specifically solar-cell window layers.

The researchers also mapped how the material’s energy band gap shifted with processing conditions, recording values of 3.31 eV for the unannealed film, 3.53 eV at 200°C, 3.14 eV at 300°C, and 3.63 eV at 400°C — consistently higher than the roughly 2.42 eV band gap of bulk CdS. They linked this overall elevation to quantum-size effects in the deposited films, while attributing the more intricate shifts between annealing temperatures to accompanying changes in oxygen incorporation, defect density, composition, and crystallinity.

Structural analysis of the unannealed film added further depth to the picture: X-ray diffraction confirmed a cubic zincblende structure, with reflections from the (111), (200), (220), and (311) planes and a preferred orientation along (111), while the Debye-Scherrer equation placed the crystallite size at roughly 8.4 nanometers along the dominant plane. Electron microscopy of the same film revealed densely packed, spherical grains forming a continuous, void-free coating, and elemental analysis confirmed the presence of cadmium and sulphur alongside a sulphur-deficient composition and an oxygen signal consistent with partial conversion of CdS to CdO during processing — the kind of compositional detail that helps explain a film’s optical response at a deeper level.

The significance of this work extends beyond a single set of measurements. By linking a simple, inexpensive processing variable to measurable gains in transmittance and band-gap shifts, Ayodimeji’s research reinforces a principle central to materials science: a semiconductor’s usefulness in a technology like a solar panel depends as much on how it is fabricated as on which material is chosen. Through this low-cost, reproducible thin-film processing, Aregbesola Ayodimeji Emmanuel contributed to the broader effort to refine established materials for next-generation photovoltaic applications, and insight of this kind could help strengthen Nigeria’s growing solar energy sector, supporting more efficient, locally produced photovoltaic components as part of a wider push towards energy security and expanded renewable power generation.