The crucial effects of the micro-structure on the properties of Nc-Si:H films for solar cells

The intrinsic hydrogenated nano-crystalline silicon (nc-Si:H) films for p-i-n tandem solar cells have been deposited by plasma enhanced chemical vapor deposition (PECVD) assisted with direct current bias, and were investigated by four-point probe sheet resistance measurement, Raman and ultraviolet-visible (UV-VIS) transmission spectra. By varying technological conditions, the dependence of the conductivity and optical properties of nc-Si:H films on the micro-structure has been discussed. Results shows: well-fabricated structure of the films result in a small optical band-gap (E_g). When amorphous content, namely lattice disorder, increases, E_g gets big. Then qualitative and quantitative analysis has carried out to get that of micro-structure´s parameters, crystal volume (X_C) influenced E_g more severely than crystalline size. With X_C varied, E_g shows a contrary change trend correspondingly. And conductivity becomes high with well-ordered micro-structure, which is directly influenced by depositing time. Besides, with substrate temperature (T_S) rising, the micro-structural properties have been improved.