Structural studies of n-type nc-Si–QD thin films for nc-Si solar cells

A wide optical gap nanocrystalline silicon (nc-Si) dielectric material is a basic requirement at the n -type window layer of nc-Si solar cells in thin film n-i-p structure on glass substrates. Taking advantage of the high atomic-H density inherent to the planar inductively coupled low-pressure (SiH 4 + CH 4 )-plasma, development of an analogous material in P-doped nc-Si–QD/a-SiC:H network has been tried. Incorporation of C in the Si-network extracted from the CH 4 widens the optical band gap; however, at enhanced PH 3 -dilution of the plasma spontaneous miniaturization of the nc-Si–QDs below the dimension of Bohr radius (∼4.5 nm) further enhances the band gap by virtue of the quantum size effect. At increased flow rate of PH 3 , dopant induced continuous amorphization of the intrinsic crystalline network is counterbalanced by the further crystallization promoted by the supplementary atomic-H extracted from PH 3 (1% in H 2 ) in the plasma, eventually holding a moderately high degree of crystallinity. The n -type wide band gap (∼1.93 eV) window layer with nc-Si–QDs in adequate volume fraction (∼52%) could furthermore be instrumental as an effective seed layer for advancing sequential crystallization in the i -layer of nc-Si solar cells with n-i-p structure in superstrate configuration.