Chemical bath deposition of mercury bismuth sulfide (HgBi2S3) sensitized titanium dioxide (TiO2) thin films: An In-depth analysis and characterization study

Mercury bismuth sulfide (HgBi2S3), a member of the II-V-VI group of semiconducting materials, has not been previously synthesized, investigated, or reported as a potential absorber layer for solar cells. This ternary metal chalcogen exhibits an optical energy band gap ranging from 1.4 to 1.7 eV, demonstrating efficient absorption in the range of 104 to 105 cm-1. In this study, thin films of titanium dioxide (TiO2) and HgBi2S3 were synthesized and deposited using spin coating and chemical bath deposition methods, respectively as a function of deposition time. The synthesized TiO2/HgBi2S3 thin film was subjected to characterization techniques including X-ray diffraction (XRD), UV-Visible spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray (EDXS) spectroscopic analysis, electrochemical impedance spectroscopy (EIS) and photoelectrochemical performance (JV) evaluation. XRD analysis confirmed the deposition of a polycrystalline thin film with an average crystalline size ranging from 401 to 789 nm, depending on the deposition time of 60 to 180 min.The average particle size of the film varied from 218 to 479 nm, and the thickness of the TiO2/HgBi2S3 thin film was measured to be between 10.14 and 12.47 mu m. After sensitization, the contact angle of the TiO2 thin film decreased from 400 to 180, and this change was independent of the deposition time of the HgBi2S3 thin film. The absorbance of the TiO2 thin film showed an increasing trend with deposition time, while the optical energy gap of TiO2 decreased from 3.12 to 1.54 eV following the deposition of the HgBi2S3 thin film. EDXS analysis confirmed the successful deposition of HgBi2S3 onto the TiO2 thin film. However, the HgBi2S3 sensitized TiO2 thin film exhibited only marginal photovoltaic performance with maximum short circuit current of 0.3537 mA/cm2 for deposition time of 60 min.