Influence of intrinsic amorphous silicon passivation layer on the dark-state stability of SHJ cells

Silicon heterojunction (SHJ) solar cells with a two-densities stacked intrinsic hydrogenated amorphous silicon (i-a-Si:H) thin film passivated crystalline silicon surface have high VOC and efficiency. We investigated the dark stability of cells varied with the microstructure of i-a-Si:H layers. It has been found that the dark degradation is mainly from the change in the silicon hydrogen bonded configuration associated with voids size. Furthermore, the less degradation exists on cells with thicker dense i-a-Si:H layers, which results from the high bonded hydrogen content after the enhanced light-soaking (LS) and less change in voids during the dark storage in the i-a-Si:H layers. The microstructure changes, including bonded hydrogen content, voids size, and voids quantity, are related to the initial microstructure of i-a-Si:H layers. This can be illustrated by two actions of non-bonded hydrogens immersed in the undense part of the silicon network. As a result, to enhance the bonded hydrogen content in the i-a-Si:H layers is a preferred method to improve the dark stability of SHJ solar cell after LS.