| dc.description.abstract | This study primarily employs plasma-enhanced chemical vapor deposition (PECVD) and chloride precursors (germanium tetrachloride and silicon tetrachloride) to independently develop the front and rear layers of germanium/silicon/glass-based tandem solar cells. The goal is to integrate these two thin films in the future.
The types of glass substrates used include alkali-free glass, quartz glass, and indium tin oxide (ITO) conductive glass. During the heating and cooling process, stress-induced wrinkles, cracks, and subsequent peeling deformations were observed in the films. When cooling from 450°C to room temperature, the germanium/quartz glass exhibited cracking deformation at a critical thickness of about 1 μm. The germanium/ITO conductive glass showed wrinkling deformation when the film was thinner (less than 200 nm) or when the deposition temperature was lower. No deformation was observed in the germanium/alkali-free glass for thicknesses up to 2 μm.
XRD patterns of germanium deposited on the three substrates showed a strong signal on the (220) crystal plane. Raman spectroscopy analysis indicated that as the thickness of the germanium film increased to 1 μm, the accumulated tensile strain in the film spontaneously released, shifting from 295 cm-1 to nearly 300.9 cm-1.
Silicon films on the three types of glass also exhibited strain-induced deformation issues. During the cooling process after deposition, silicon films on alkali-free glass showed wrinkling deformation and peeling at a critical thickness of less than 200 nm. Additionally, during thermal annealing from room temperature to 450°C, silicon films on quartz glass showed wrinkling deformation and peeling, while no deformation was observed for silicon films on ITO glass up to a thickness of 1 μm.
Furthermore, a technique for in-situ gallium doping was developed. Using gallium trichloride as a precursor, doping was carried out simultaneously during the deposition of the germanium film, achieving a minimum resistivity of 0.001 Ω·cm.
In this study, thin-film solar cells developed on glass substrates did not yet show reliable conversion efficiency, only achieving a value close to the instrument′s error margin of 10^-6%. The resistivity of the pure germanium film measured with a four-point probe was as low as 0.12 Ω·cm, suggesting accidental impurity incorporation during the deposition process. Temporarily shifting focus to developing germanium/N-type silicon substrate solar cells resulted in a conversion efficiency of 6.2%, with a short-circuit current density of 54.2 mA/cm², an open-circuit voltage of 310 mV, and a fill factor of 38.2%. | en_US |