Synthesis and characterization of Cu2S/ZnO–Chlorophyll:p-Si nanocomposite thin films by pulsed laser deposition for silicon-based photovoltaic applications

Cu₂S/ZnO–Chlorophyll Nanocomposite thin films were successfully fabricated on p-Si substrates by combining hydrothermal synthesis with pulsed laser deposition in order to construct hybrid heterojunction structures for energy-harvesting applications. The results showed that increasing the laser deposition energy from 80 mJ (1st sample: CZC-80) to 160 mJ (2nd sample: CZC-160) significantly improved the structural quality of the films, enhanced compositional homogeneity, and promoted better interfacial definition within the heterostructure. In the XRD characteristics of the samples, a multi-scale granular structure is observed in two samples across atomic to macroscopic scales: spherical grains with crystallite sizes ranging from 40 to 90 nm. EDX analysis of CZC-80 revealed a weak C signal at 0.3 keV (chlorophyll), a pronounced O peak at 0.53 keV (ZnO), overlapping Cu Lα/Zn Lα signals at 0.9–1.1 keV, and strong Cu Kα (8.0 keV), Zn Kα (8.6 keV), and Zn Kβ (9.6 keV) emissions, confirming the Cu₂S/ZnO–chlorophyll composite. The CZC-160 film exhibited significantly higher peak intensities at these energies, indicating higher Cu and Zn concentrations than CZC-80. Optical characterization revealed strong absorption in the UV region for all samples, where CZC-160 exhibited an absorption edge at ∼349 nm (vs. ∼343 nm for CZC-80), a narrower band gap (3.549 eV vs. 3.614 eV), lower transmittance, higher refractive index and extinction coefficient, indicating denser microstructure, enhanced photon interaction. However, the film deposited at higher laser energy exhibited lower transmittance and a slight reduction in optical band gap that decreased from 3.614 eV (CZC-80) to 3.549 eV (CZC-160); a narrowing of 0.065 eV at higher laser energy due to improved crystallinity and interfacial electronic coupling, which may be attributed to denser packing and stronger electronic interaction among the Cu₂S, ZnO, and Chlorophyll components. The refractive index and extinction coefficient results further confirmed improved photon interaction and a more compact optical structure for the film prepared at 160 mJ. Hall-effect measurements indicated that n-type conductivity increased from 2.36 36 × × 10⁻⁵ to 2.53 × 10⁻⁵ (Ω·cm)⁻¹ in two samples, while the device fabricated at 160 mJ exhibited a decrease in resistivity from 7.99 × 10⁴ to 5.02 02 × × 10⁴ Ω·cm and improved charge-transport characteristics at higher energy. In addition, both dark and illuminated I-V measurements displayed nonlinear rectifying behavior typical of a p-n heterojunction, with a clear photoresponse under illumination. Among the fabricated devices, the sample prepared at 160 mJ exhibited the best photovoltaic performance, achieving a Fill factor (0.47) with a conversion efficiency of approximately 9.1 %. Overall, the findings demonstrate that Cu₂S/ZnO–Chlorophyll hybrid nanocomposite films are promising materials for UV-responsive optoelectronic devices and silicon-based photovoltaic applications.