Structural analyses of seeded thin film microcrystalline silicon solar cell

This contribution investigates the effect of seeding the growth of thin film microcrystalline silicon (µc-Si¿:¿H) deposited by radio frequency plasma-enhanced chemical vapor deposition on the material properties of µc-Si¿:¿H film and the device performance of p-i-n and n-i-p µc-Si¿:¿H solar cells. By means of Raman measurement, x-ray diffraction (XRD) and transmission electron microscopy (TEM), we investigate the structure of seeded µc-Si¿:¿H. In particular, the effect of seed layers on the crystallinity development is investigated. Measurements of the depth profile of the crystalline mass fraction using Raman spectroscopy show that seed layers lead to a more rapid and uniform crystallinity development in growth direction. The amorphous incubation layer is suppressed and crystallization begins directly from onset of film growth without evolving through the intermediate growth phases. From TEM analyses, we observe that crystal sizes are not affected by seed layers. Horizontal cracks are however observed to dominate the early growth of µc-Si¿:¿H in p-i-n solar cell and this is reduced upon seeding. For the n-i-p cells, these cracks are not affected by seeding. XRD results also indicate that the use of seed layers does not affect the crystal sizes but affects the direction of preferential orientation. Solar cell external parameters show that seeding of p-i-n solar cells leads mainly to increase in short-circuit current density, Jsc with a slight drop in open-circuit voltage, Voc. For the n-i-p cells, a reverse effect is observed. In this case, the Voc increases and the Jsc decreases.