Structural inhomogeneities in polycrystalline silicon on glass solar cells and their effects on device characteristics

The effects of electrostatic fluctuations due to charged extended defects and strain‐induced bandgap fluctuations are examined in polycrystalline silicon on glass solar cells. The analysis is based on models previously applied to Cu(In,Ga)Se2 solar cells, but with a new interpretation of the local ideality factor associated with electrostatic fluctuations. It is shown that electrostatic fluctuations become influential to the cell voltage properties as the absorber dopant concentration falls below a certain threshold (a few 1015 cm−3), and the degradations to the open circuit voltage and fill factor are expected to increase with further lowering of dopant density. It is equally plausible that the electrostatic fluctuations originate from charged dislocations or grain boundaries. Bandgap fluctuations on the other hand can be detrimental to the open circuit voltage of cells of any absorber dopant density. However, this voltage degrading effect is seen only in the cells deposited by electron‐beam evaporation, and not amongst those made by plasma enhanced chemical vapour deposition. Copyright © 2011 John Wiley & Sons, Ltd.

[1]  M. Green,et al.  Anomalous temperature dependence of diode saturation currents in polycrystalline silicon thin-film solar cells on glass , 2009 .

[2]  E. Umbach,et al.  Lateral inhomogeneities of Cu(In,Ga)Se2 absorber films , 2000 .

[3]  C. H. Seager,et al.  Grain boundary recombination: Theory and experiment in silicon , 1981 .

[4]  W. Schröter,et al.  Investigation of the Defect Distribution in Polycrystalline Silicon , 1994 .

[5]  J. Seto.  The electrical properties of polycrystalline silicon films , 1975 .

[6]  L. Kazmerski,et al.  Chemical, compositional, and electrical properties of semiconductor grain boundaries , 1982 .

[7]  Martin A. Green,et al.  General temperature dependence of solar cell performance and implications for device modelling , 2003 .

[8]  M. Green,et al.  Lifetime limiting recombination pathway in thin-film polycrystalline silicon on glass solar cells , 2010 .

[9]  A. Stesmans,et al.  High open-circuit voltage values on fine-grained thin-film polysilicon solar cells , 2006 .

[10]  A. W. Blakers,et al.  Silicon solar cells with reduced temperature sensitivity , 1982 .

[11]  E. Yang,et al.  Electronic processes at grain boundaries in polycrystalline semiconductors under optical illumination , 1977, IEEE Transactions on Electron Devices.

[12]  D. P. Joshi,et al.  Theory of grain boundary recombination and carrier transport in polycrystalline silicon under optical illumination , 1990 .

[13]  Jürgen H. Werner,et al.  Efficiency limitations of polycrystalline thin film solar cells: case of Cu(In,Ga)Se2 , 2005 .

[14]  W. Schröter,et al.  Recombination activity of contaminated dislocations in silicon: A model describing electron-beam-induced current contrast behavior , 2001 .

[15]  Broniatowski.  Measurement of the grain-boundary states in semiconductors by deep-level transient spectroscopy. , 1987, Physical review. B, Condensed matter.

[16]  Armin G. Aberle,et al.  Progress with polycrystalline silicon thin-film solar cells on glass at UNSW , 2006 .

[17]  S. Varlamov,et al.  5% Efficient evaporated solid‐phase crystallised polycrystalline silicon thin‐film solar cells , 2009 .

[18]  Jürgen H. Werner,et al.  Modeling of spatially inhomogeneous solar cells by a multi‐diode approach , 2005 .