Unveiling improvements in structural, optical, and photodetection characteristics of CZTS thin films through Ag-doping

The study investigated the characterization of photodetectors made from CZTS (Cu₂ZnSnS₄) thin films by introducing silver (Ag) as a dopant. CZTS thin films were grown on Mo-foil by two stage process, comprising sputter deposition of metallic precursor layers followed by sulfurization process employing Rapid Thermal Annealing (RTA) approach. The stacking order for the undoped and Ag-doped CZTS thin films were Substrate/ZnS/Cu/Sn/Cu and Substrate/ZnS/Cu/Sn/Cu/Ag, respectively. Photodetectors (PDs) were fabricated using sputter deposition on glass, including CZTS, Ag-doped CZTS-5 (8 nm Ag), Ag-doped CZTS-10 (16 nm Ag), and Ag-doped CZTS-15 (24 nm Ag). Various characterization methods were utilized to examine the prepared thin films, including Energy Dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy, Scanning Electron Microscopy (SEM), optical transmission, Photoluminescence (PL) and photodetection analyses. Among all devices, Ag-CZTS-10 PDs exhibited the best performance, showing a crystallite size (D) of 51.72 nm, band gap of 1.47 eV and favorable SEM surface morphology. For the photodetection characteristics, blue light at 443 nm and red light at 525 nm wavelength were used with an applied bias of 2V, and a light intensity of 17.3 mW/cm². The highest responsivity (R) values recorded for Ag-CZTS-10-based PDs were 0.0024 A/W for blue and 0.0019 A/W for red light. Additionally, the detectivity (D∗) was 3.4 × 10⁶ Jones for blue and 2.3 × 10⁶ Jones for red light, while sensitivity (S) was 26 % for blue and 15 % for red light. This study successfully demonstrated, for the first time, the fabrication of low-cost, high-performance Ag-doped CZTS films-based PDs on glass substrates which hold promise for the development of cost-effective and efficient optoelectronic devices.