alexa Incorporation of p-type microcrystalline silicon films in amorphous silicon based solar cells in a superstrate structure
Engineering

Engineering

Journal of Electrical & Electronic Systems

Author(s): JK Rath, REI Schropp

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Thin (<20nm) p-type microcrystalline silicon films have been deposited by plasma enhanced chemical vapor deposition in a parameter regime, specifically optimized for extremely thin films. High conductivity (>10 - 2 Ω - 1 cm - 1 ) and low activation energy (<0.08eV) have been achieved for thin films on various oxide substrates i.e., Corning 7059 glass, SnO 2 :F, TiO 2 and Ta 2 O 5 . Deposition of thin p-μc-Si:H is possible on void rich films (a-SiC:H and low-temperature deposited a-Si:H) but not on device quality a-Si:H. Single junction p-i-n cells were made in a superstrate structure using p-μc-Si:H as the window layer directly on top of SnO 2 :F coated glass. For the first time an efficiency of 9.63% could be achieved for a single junction cell with a truly microcrystalline silicon p-layer in a superstrate configuration. There is an improvement in the blue spectral response compared to the cell made with a-SiC:H(B) as window layer. However, open circuit voltage and fill factor were critically dependent on the choice of buffer layer at the p/i interface. Computer simulations point out that this can be attributed to the valence band offset between the amorphous i-layer and the microcrystalline p-layer. The buffer acts as a barrier to electron back-diffusion and reduces the recombination in the p-layer. Tandem cells (a-Si:H/a-Si:H) incorporating p-μc-Si:H along with n-μc-Si:H in the tunnel junction showed an efficiency of 9.9% and FF of 0.73. The tunnel junction n-μc-Si:H/p-μc-Si:H needed an oxide interface layer for a good performance. The role of the interface layer may be to increase the tunnel recombination as well as to act as a diffusion barrier to dopants.

This article was published in Solar Energy Materials and Solar Cells and referenced in Journal of Electrical & Electronic Systems

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