Effects of Cadmium Chloride Treatment on Selenium Diffusion in Thin-Film Cadmium Telluride Photovoltaics

• Jacob Peterson, Material Science, University of Delaware

• William Shafarman, Material Science and Engineering, University of Delaware

Thin-film cadmium telluride (CdTe) solar cells remain a promising photovoltaic technology due to their high efficiency and low manufacturing cost. In most devices, a thin layer of selenium is deposited before the CdTe, which is then diffused during later processing. The CdSeTe produced is crucial for cell performance, as the added selenium lowers the band-gap energy and improves defect passivation. Selenium alloying can be combined with other passivation methods, including cadmium chloride (CdCl₂) treatments. CdCl₂ treatments are especially effective because they target the grain boundaries, which are the areas most prone to these defects. Recently, new evidence has suggested making changes to how these CdCl₂ treatments are performed. This study investigates how new adjustments to the CdCl₂ treatment procedure will influence selenium diffusion from the CdSe front layer into the CdTe absorber. Several bilayer solar cells were fabricated and treated with an initial spin-coat of a CdCl₂ solution followed by a CSS treatment with pure CdCl₂. Device performance was then evaluated using current density-voltage (J-V) measurements to assess the electrical response following each treatment. To examine structural changes associated with selenium diffusion, the devices were delaminated to expose the front surface for X-ray diffraction (XRD) characterization. Comparing electrical performance with structural characterization provides insight into the relationship between CdCl₂ processing conditions, selenium diffusion, and device properties. This work aims to improve our understanding of the role of CdCl₂ treatment in CdSe/CdTe solar cells and to identify processing conditions that promote favorable material properties and photovoltaic performance. These findings may contribute to the optimization of thin-film CdTe solar cell fabrication and support the continued development of high-efficiency photovoltaic devices.