Development of Optimal Nanocrystalline Absorption Layer for Thin Film Silicon Solar Cell Applications.

To obtain an optimum absorption layer based on hydrogenated polymorphous and nanocrystalline silicon thin films in a plasma-enhanced chemical vapor deposition, radio frequency (RF) power was varied from 25W to 100W using a mixture of dichlorosilane and hydrogen. By Raman spectroscopy, the crystalline fraction was found to be varied from 7% to 69%, and RF power value of 75W was found to be suitable with an appropriate mixture of amorphous and crystalline phases, respectively. Thickness measurements performed by profilometry were cross-checked with the value obtained from the cross-sectional scanning electron microscopy micrographs. Micrographs obtained using high-resolution transmission electron microscopy confirmed the presence of silicon nanocrystals in the range of 2-5nm with a strong probability of confinement effect. B and gap value of 1.55eV at 75W upheld the suitability of this particular RF power for active absorption layer, which has also shown maximum photosensitivity. By varying the RF power in a plasma-enhanced chemical vapor deposition (PECVD) system, control over the morphology and phase transition (a-Si to nc-Si) of silicon thin films has shown. Furthermore, control over the size of nanoparticles and hence, effective band gap (absorption coefficient) of the material is also reported. Overall, the use of the present material as a proficient absorption layer in silicon solar cells shown excellent optoelectronic properties. [ABSTRACT FROM AUTHOR]