Microcrystalline silicon tunnel junctions for amorphous silicon-based multijunction solar cells
The formation of tunnel junctions for applications in amorphous silicon (a-Si:H) based multijunction n-i-p solar cells has been studied using real time optics. The junction structure investigated in detail here consists of a thin ({approximately} 200 {angstrom}) layer of n-type microcrystalline silicon ({micro}c-Si:H) on top of an equally thin layer of p-type {micro}c-Si:H, the latter deposited on thick ({approximately} 2,000 {angstrom}) intrinsic a-Si:H. Such a structure has been optimized in an attempt to obtain single-phase {micro}c-Si:H with a high crystallite packing density and large grain size for both layers of the tunnel junction. They have explored the conditions under which grain growth is continuous across the p/n junction and conditions under which renucleation of n-layer grains can be ensured at the junction. one important finding of this study is that the optimum conditions for single-phase, high-density {micro}c-Si:H n-layers are different depending on whether the substrate is a {micro}c-Si:H p-layer or is a H{sub 2}-plasma treated or untreated a-Si:H i-layer. Thus, the top-most {micro}c-Si:H layer of the tunnel junction must be optimized in the multijunction device configuration, rather than in single cell configurations on a-Si:H i-layers. The observations are explained using an evolutionary phase diagram for a-Si:H and {micro}c-Si:H film growth versus thickness and H{sub 2}-dilution ratio, in which the boundary between the two phases is strongly substrate-dependent.
- Research Organization:
- Pennsylvania State Univ., University Park, PA (US)
- Sponsoring Organization:
- National Science Foundation; National Renewable Energy Laboratory
- OSTI ID:
- 20107956
- Country of Publication:
- United States
- Language:
- English
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