Recent Progress in Understanding the Properties of the Amorphous Silicon/Crystalline Silicon Interface

The authors review experimental and modeling approaches developed at GeePs to have a better knowledge and understanding of the interface between hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si) in heterojunction solar cells. The authors emphasize the existence of a strong inversion layer at the c-Si surface for both (n) a-Si:H/(p) c-Si and (p) a-Si:H/(n) c-Si heterojunctions. Conductive probe atomic force microscopy reveals the existence of a conductive channel at the c-Si surface. The analysis of complementary lateral planar conductance and capacitance measurements allows for a better description of the band diagram in both types of heterojunctions especially through the determination of band offset values. Furthermore, the passivation properties of the (i) a-Si:H buffer layer are studied by modeling the volume defects in a-Si:H with the defect-pool model. In particular, the DOS in the very thin (i) a-Si:H layers is much larger than in bulk (i) a-Si:H because the Fermi level position favors defect creation. Surface defects in c-Si at the a-Si:H/c-Si interface are then quantified and the general trends of effective lifetime measurements with the (i) a-Si:H layer thickness can be explained, notably the increase of the effective lifetime in c-Si with increasing the (i) a-Si:H buffer thickness.