Fig. 3: Electrical and microstructure characterizations as well as band alignment analysis of HSCs based on p-a-Si:H and p-nc-Si:H.
a, Raman spectra collected from p-a-Si:H–i-a-Si:H–glass and p-nc-Si:H–i-a-Si:H–glass samples. Gaussian fitting (colour shaded areas) was implemented on the characteristic peaks at 478 cm–1 (a-Si:H) and at 507 and 518 cm–1 (nc-Si:H)42,43. The XC was calculated by equation (1). b,c, TEM images of TCO–p-a-Si:H–i-a-Si:H–n-Si (b) and TCO–p-nc-Si:H–i-a-Si:H–n-Si (c) structures. The TEM images were captured on the Si (110) cross-section, and the corresponding FFT images (insets) were mathematically obtained. Crystallites in p-nc-Si:H with different orientation are distinguished by colour, and the corresponding reciprocal spots in FFT images are highlighted with coloured circles. The red arrows depict the growth direction of the silicon thin films on the Si (111) plane. d, Extraction of Ea for p-nc-Si:H and p-a-Si:H films without light soaking following equation (2) (dotted lines)49. e,f, Equilibrium band diagrams of HSCs based on p-a-Si:H (e) and p-nc-Si:H (f) related to the cross-sectional structures in b and c. EC, EV and EF denote conduction band energy, valence band energy and Fermi level, respectively. Insets: enlarged view of the black wire frames; there, ΔE equals the difference between EF and EV at the i-a-Si:H–n-Si interface. The collection path of holes across the heterojunction is depicted as a more complicated curve (red arrows) for p-a-Si:H to illustrate a more challenging transport mechanism at the relative interfaces, with respect to the p-nc-Si:H counterpart. Current is generated once the holes meet and recombine with the electrons (along blue arrows) at the interface of the TCO–hole transport layer.
