Recent Advancements in Chemical Bath Deposited Pristine CDs Thin Films For Hotovoltaic Applications

Cadmium sulfide (CdS) is (II–VI) group n-type semiconductor with appreciable physical and electronic properties. The wide band gap of about 2.42 eV, large absorption coefficient of 4×104 cm−1 and high mobility (440 cm2 V-1 s-1) make it applicable in photovoltaic energy conversion. Consequently, CdS is considered an excellent window material as well as a buffer layer for almost all chalcogenide thin film technologies, including copper zinc tin selenide (CZTSe), copper indium gallium selenide (CIGS) and CdTe-based solar cells. However, the defects present in the CdS thin films, such as inter-granular caves and pin holes, relaxation losses due to excess photon energy, and carrier recombination, can potentially affect the low light-to-current conversion efficiency with respect to the theoretical value of the above solar cells. Many studies have been carried out to produce CdS thin films with good optoelectronic properties suitable for photovoltaic applications. Among the numerous methods of depositing CdS, chemical bath deposition (CBD) stands out as a simple and low-cost method to prepare high-quality CdS thin films among those methods. However, the efficiency of resultant CBD-CdS thin films is strongly dependent on several parameters that should be very carefully adjusted: composition of the solution, especially sources, and concentration of sulfur and cadmium ions, pH and temperature of deposition bath, as well as the duration of the deposition on the morphology and quality of the CdS films. Additionally, doping, hydride methods, and surfactant-assisted deposition approaches are also performed to enhance the physical properties of the CdS. Regardless of the deposition technique, the post-deposited films' characterisation and deposition process optimisations are still an open subject. This review article describes the recent approaches to enhance the optoelectrical properties of the CBD CdS thin films and their recent advance in photovoltaic applications.