Design Aspects of Silicon Thin Film Solar Cells

3 Design Aspects of Silicon Thin Film Solar Cells 

Here we describe the layer structure for single junction as well as for tandem solar cells consisting of a-Si H and pc-Si l I. Further, this section will deal with the stability of silicon thin film solar cells and the possibility to reduce degradation by special design. 

The doped and intrinsic silicon layers (p, i, n) are packed between a TCO front contact and a highly reflective back contact. The back contact is usually either a metal like silver (Ag) or aluminum (Al), or a TCO/metal double layer structure. The latter has been shown to reduce absorption losses due to a better grain growth of Ag layers onto ZnO. Additionally, absorption losses due to surface plasmons in the metal film have to be considered [33]. Both effects result in a higher reflectivity of the TCO/Ag back reflector. In module production, magnetron sputtered ZnO is usually applied as TCO-material for the back reflector in combination with either Ag (highest reflectivity) or Al (low cost). Depending on the deposition sequence of the doped and intrinsic silicon layers, one speaks of so-called superstrate (p-i-n) or substrate (n-i-p) cell structure (see Fig. 8.4). 

In this paragraph we will briefly discuss the stability behavior of silicon thin film solar cells. Two aspects were considered light induced degradation and stability in hot and humid environment. 

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