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Protocrystalline Si:H p-type Layers for Maximization of the Open Circuit Voltage in a-Si:H n-i-p Solar Cells

Published online by Cambridge University Press:  01 February 2011

R. J. Koval
Affiliation:
Materials Research Institute, Center for Thin Film Devices, and Department of Physics, The Pennsylvania State University, University Park, PA 16802.
Chi Chen
Affiliation:
Materials Research Institute, Center for Thin Film Devices, and Department of Physics, The Pennsylvania State University, University Park, PA 16802.
G. M. Ferreira
Affiliation:
Materials Research Institute, Center for Thin Film Devices, and Department of Physics, The Pennsylvania State University, University Park, PA 16802.
A. S. Ferlauto
Affiliation:
Materials Research Institute, Center for Thin Film Devices, and Department of Physics, The Pennsylvania State University, University Park, PA 16802.
J. M. Pearce
Affiliation:
Materials Research Institute, Center for Thin Film Devices, and Department of Physics, The Pennsylvania State University, University Park, PA 16802.
P. I. Rovira
Affiliation:
Materials Research Institute, Center for Thin Film Devices, and Department of Physics, The Pennsylvania State University, University Park, PA 16802.
C. R. Wronski
Affiliation:
Materials Research Institute, Center for Thin Film Devices, and Department of Physics, The Pennsylvania State University, University Park, PA 16802.
R. W. Collins
Affiliation:
Materials Research Institute, Center for Thin Film Devices, and Department of Physics, The Pennsylvania State University, University Park, PA 16802.
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Abstract

We have revisited the issue of p-layer optimization for amorphous silicon (a-Si:H) solar cells, correlating spectroscopic ellipsometry (SE) measurements of the p-layer in the device configuration with light current-voltage (J-V) characteristics of the completed solar cell. Working with p-layer gas mixtures of H2/SiH4/BF3 in rf plasma-enhanced chemical vapor deposition (PECVD), we have found that the maximum open circuit voltage (Voc) for n-i-p solar cells is obtained using p-layers prepared with the maximum possible hydrogen-dilution gas-flow ratio R=[H2]/[SiH4], but without crossing the thickness-dependent transition from the a-Si:H growth regime into the mixed-phase amorphous + microcrystalline [(a+μc)-Si:H] regime for the ∼200 Å p-layers. As a result, optimum single-step p-layers are obtained under conditions similar to those applied for optimum i-layers, i.e., by operating in the so-called “protocrystalline” Si:H film growth regime. The remarkable dependence of the p-layer phase (amorphous vs. microcrystalline) and n-i-p solar cell Voc on the nature of the underlying i-layer surface also supports this conclusion.

Type
Research Article
Copyright
Copyright © Materials Research Society 2002

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