Fabrication of pulsed laser deposited Ge doped CZTSSe thin film based solar cells: Influence of selenization treatment

Abstract In the present work, Ge doped CZTGeS thin films are pulsed laser deposited followed by annealing treatment in selenium environment. The influence of selenization condition on the structural, morphological, optical and electrical properties of the absorber thin films are investigated. The thin films characterized using X-ray diffraction (XRD) and Raman spectroscopy techniques confirm the formation of Kesterite CZTGeSSe thin film compound with dominant A1 mode vibration. The morphological and optical studies of the thin films reveal the formation of compact and void free microstructure with optimal band gap in the range of 1–1.2 eV. The impact of selenization temperature on the quality of thin films has been studied and thin film solar cells are fabricated with CZTGeSSe absorbers grown at various annealing temperatures from 525 to 575 ℃ to evaluate the performance of devices as a function of an annealing temperature. The elemental Ge and Sn losses from the absorber compound confirmed from X-ray fluorescence spectroscopy (XRF) depended on the annealing temperature and linearly increased with increasing temperature affecting the optical, compositional and microstructural properties of the thin films. Compositional non uniformity is one of the factors that limit the performance of solar cell device. PLD technique due to its advantage of achieving precise stoichiometry control combined with optimized selenization conditions can potentially address the issue. Compared to solar cell fabricated from absorber compound annealed at 525 and 575 ℃, the solar cell fabricated from the absorber annealed at 550 ℃ exhibited the best conversion efficiency of 3.82% with Voc 434 mV, Jsc 18.33 mA/cm2, FF 47.0% and retained nearly 90% power conversion efficiency (PCE) stability after time period of 60 days.