The Effects of Hydrogen Iodide Back Surface Treatment on CdTe Solar Cells

An appropriate electrical back contact in CdTe solar cells is crucial to achieving high power conversion efficiency. In this work, a facile back surface treatment method for CdTe solar cells using hydroiodic acid (HI) is developed, and the effects of HI etching on the CdTe surfaces investigated. The electrical properties of the CdTe absorber and interfaces are characterized by current-voltage, capacitance-voltage, admittance spectroscopy, and complex capacitance spectroscopy measurements. The HI-etched devices show slightly higher apparent carrier concentrations than the control devices, suggesting an increased copper doping in the CdTe absorber. The potential barrier height of the back contact is reduced from 0.430 to 0.368 eV after the HI-treatment, accompanied by reduced contact resistance and carrier recombination. Additionally, the HI-treatment eliminates a defect signature at 0.409 eV. The HI-treatment effects lead to improved power conversion efficiency through enhancement of the fill factor, the short circuit current, and open circuit voltage.