Wide gap microcrystalline silicon carbide emitter for amorphous silicon oxide passivated heterojunction solar cells

Abstract

Wide gap n-type microcrystalline silicon carbide [µc-SiC:H(n)] is highly suitable as window layer material for silicon heterojunction (SHJ) solar cells due to its high optical transparency combined with high electrical conductivity. However, the hot wire chemical vapor deposition (HWCVD) of highly crystalline µc-SiC:H(n) requires a high hydrogen radical density in the gas phase that gives rise to strong deterioration of the intrinsic amorphous silicon oxide [a-SiOx:H(i)] surface passivation. Introducing an n-type microcrystalline silicon oxide [µc-SiOx:H(n)] protection layer between the µc-SiC:H(n) and the a-SiOx:H(i) prevents the deterioration of the passivation by providing an etch resistance and by blocking the diffusion of hydrogen radicals. We fabricated solar cells with µc-SiC:H(n)/µc-SiOx:H(n)/a-SiOx:H(i) stack for the front side and varied the µc-SiOx:H(n) material properties by changing the microstructure of the µc-SiOx:H(n) to evaluate the potential of such stack implemented in SHJ solar cells and to identify the limiting parameters of the protection layer in the device. With this approach we achieved a maximum open circuit voltage of 677 mV and a maximum energy conversion efficiency of 18.9% for a planar solar cell.