Effects of annealing temperature on crystallisation kinetics, film properties and cell performance of silicon thin-film solar cells on glass

Solid-phase crystallisation (SPC) of Si films on glass prepared by three deposition methods, plasma enhanced chemical vapour deposition (PECVD), electron-beam evaporation, and a combination of both, are compared for different annealing temperatures. Three independent techniques, optical transmission microscopy, UV reflectance spectroscopy, and X-ray diffraction, are used to characterise the crystallisation kinetics and film properties. The activation energy for the incubation is estimated to be 2.7–3.0 eV. The scanning electron microscopy images of polycrystalline Si films after Secco etching show a gradually decreasing average grain size in each film type for higher SPC temperatures. The crystal quality of all film types degrades at higher crystallisation temperatures. Solar cells fabricated from these polycrystalline Si films were characterised by Suns-Voc and spectral response measurements. According to both the resulting open-circuit voltage and the short-circuit current, the electronic quality of all polycrystalline Si film types and the corresponding cell performance degrade for higher crystallisation temperatures but to a different extent depending on the film deposition method.

► Average Si grain size dramatically declines at the higher temperature.
► Lower annealing temperatures results in slightly better Si crystal quality.
► Trade-off between decreasing cell performance and increasing process speed.
► 8× faster annealing process induces only 0.2% pseudo-efficiency reduction.