Optical losses of CdS films on FTO, ITO, and AZO electrodes in CdTe–HgCdTe tandem solar cells

Improving the spectral transmittance of CdS films used in CdTe–HgCdTe tandem solar cells has a great impact on the effective utilization of sunlight and increases the device short-circuit current density (J_sc). Herein, the optical losses of as-deposited and CdCl₂ annealed CdS films on different types of transparent conductive oxide are first studied in the visible to near infrared wavelength range. In the ranges 520–820, 820–1150, and 520–1150 nm, the average transmittance and the J_sc losses of the CdS films are closely related to the transparent conductive oxide type. CdCl₂ annealing improves the average transmittance and reduces the J_sc losses of the annealed CdS films. Bilayer films of AZO and annealed CdS exhibit the minimum J_sc loss of 3.33 mA/cm² for the CdTe top cell, bilayer films of ITO and annealed CdS exhibit the minimum J_sc loss of 3.46 mA/cm² for the HgCdTe bottom cell, and bilayer films of AZO and annealed CdS exhibit the minimum J_sc loss of 7.20 mA/cm² for the CdTe–HgCdTe solar cells.