5.91%-efficient Sb₂Se₃ solar cells with a radio-frequency magnetron-sputtered CdS buffer layer

Superstrate ITO/CdS/Sb₂Se₃/Au thin-film solar cells were fabricated with a CdS film produced by a radio-frequency (RF) magnetron-sputtering method as the buffer layer. The effect of the CdS layer thickness (70–120 nm) on the properties of Sb₂Se₃ thin films and the performance of the solar cells was investigated. The optimal CdS thickness was 90 nm, which led to the best power conversion efficiency of 5.91%; to the best of our knowledge, this is the highest efficiency for Sb₂Se₃ solar cells with a sputtered CdS buffer layer to date. X-ray diffraction and scanning electron microscope results indicated that the Sb₂Se₃ films grown on 90-nm-thick CdS layers had the optimal grain orientation and the best morphology. The current–voltage (J–V) and admittance results indicated that the Sb₂Se₃ cell with a 90-nm-thick CdS layer had the lowest saturation current and the smallest defect densities. Moreover, temperature- and light intensity-dependent open-circuit (V_oc) measurements revealed that the carrier recombination rates at the CdS/Sb₂Se₃ interface, space-charge region (SCR), and quasi-neutral region (QNR) all achieved the smallest value for the Sb₂Se₃ cells with a 90-nm CdS buffer layer. These data account for the optimal cell performance and offer new research directions for solving challenges of chemical bath deposition of CdS in Sb₂Se₃ solar cells.