Low temperature p+ nc-Si:H window layers for large area thin-film solar cells

Hydrogenated nanocrystalline silicon (nc-Si:H) has attracted attention recently over amorphous silicon (a-Si:H) for use in thin-film solar cell applications primarily due to its higher stability and light absorbing capacity. In addition, there is increasing interest in device fabrication on low-cost, light weight and flexible substrates where optimizing deposition conditions of nc-Si:H thin films at low substrate temperatures (< 200 °C) poses challenges. In such solar cells, the thin boron-doped (p+) window layer significantly determines crystalline growth of the overlying intrinsic absorber layer, quality of which eventually governs device performance. In this research, material properties of thin p+ nc-Si:H films (50 – 300 nm) were investigated. Samples were deposited using plasma enhanced chemical vapor deposition (PECVD) at low temperatures (75 or 150 °C) with various RF power and/or pressure conditions. Results from characterization experiments and feasibility of incorporating such low-temperature thin p+ nc-Si:H films as solar cell window layers are discussed.