Oras A. Al-Ani 1 St year PhD student Supervisors J. P. Goss, N. E. B. Cowern and P. R. Briddon Newcastle university

Outline  Photovoltaic (PV) : {Principle, performance, problem, materials} {Principle, performance, problem, materials}  mc-Si defects: { Fe, GB, gettering} { Fe, GB, gettering}  Methodology.  Results:  Interstitial iron () in Si.  Interstitial iron (Fe i ) in Si.  Perfect grain boundary (GB).  decorated GB.  Fe i decorated GB.  Conclusion.

PV fundamentals

Performance factors Light intensity Humidity and temperature Material type

The problem! “ The basic commercialization problem PV technology has faced for 20 years : markets will explode when module costs decline, but module costs can't decline much, until the market grows much larger “… “ The basic commercialization problem PV technology has faced for 20 years : markets will explode when module costs decline, but module costs can't decline much, until the market grows much larger “… [PV Insider's Report] [PV Insider's Report]

PV material Ref.[

 monocrystalline or (single crystal) PV cells  Grows in one direction.  More expensive to manufacture.  higher efficiency  Polycrystalline or (multicrystalline) PV cells  grows in multiple directions.  considerably lower efficiency.  Accounts for 90% of crystalline Si market.

Why still Si ?? > 90% silicon and multisilicon High efficiency Abandant and cheep Non-toxic reliable and existant technology a broad knowledge of Si material and its devices

Fe in Si Fe in Si Most common, dominant and unavoidable. A. A. Istratov, etal, A. A. Istratov, etal, D. M acdonald, etal, 2005.D. M acdonald, etal, Higher concentration Buonassisi, T., et al., Coletti, G., et al., 2008.

Fe at GB Fe at GB GB gettering Fe impurities T. Shi, etal., R. Maximilian,2012.

GB Geometry

Methodology These calculations have been studied by first principles quantum mechanics with: Density functional theory (DFT), Local density approximation (LDA), HGH pseudo potential, Gaussian basis set,

Results Fei Mobility

Fe i Fe-Si bond length=2.38 Å, angle=35.26 & deg. Si-Si bond length =3.88 Å, angle=60 deg.

Spin and charge states energies for different cell sizes Formation energy 64 –Si atoms= 0.8 eV and 1.3 eV in 512 –Si atoms. It is confirmed with Ref.[Sanati,et al, 2007 and Heiser et al, 1991]

Activation energyActivation energy Experimental and theoretical collected data for activation energy in eV The comparative data are taken from Ref. [Estreicher, et al, 2011].

GB energy density

Segregation

Conclusion

Thanks for your listening

Questions?