Modeling of the Dynamic Amorphous Silicon Thin-Film Solar Cell Deposition

The plasma enhanced chemical vapour deposition of a-Si:H p-i-n solar cells with substrate movement (dynamic deposition) using linear very high frequency plasma sources is investigated experimentally and theoretically. The absorber layer properties of the dynamically deposited a-Si:H solar cells were studied with respect to non-uniformities of the film material within the depth of the intrinic layer. This inhomogeneity in the depth profile is caused by the variation of the deposition conditions in the plasma along the transport direction of the substrate. Strong variations of the hydrogen content, microstructure parameter, optical band gap and deposition rate could be observed as a function of the lateral position in the process chamber and in consequence as a function of the vertical position in the i-layer. Dynamically deposited a-Si:H solar cells exhibit a slightly decreased fill factor and efficiency compared to statically deposited solar cells. A model of a dynamically deposited a-Si:H solar cell with a fivefold divided i-layer is proposed. The model explains the fill factor decrease by means of a limited electron collection efficiency in the inhomogeneous absorber layer. However, the fill factor loss is only marginal and could be reduced by a reduction of VHF-power during the i-layer deposition.