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The Australian National University

Silicon Materials


Our research aims to improve the quality of silicon materials used for solar cells, therefore increasing the efficiency and reducing the cost of silicon photovoltaics.

Low-cost silicon materials for solar cells, such as multicrystalline silicon wafers, or solar-grade silicon feedstocks, often contain significant quantities of unwanted impurities. Our research aims to understand the effects of these impurities, and to develop practical ways to reduce their impact, or remove them. There are several classes of important impurities: dopants (such as B, P and Al), which are very difficult to remove during purification; metals (such as Fe, Cr, Ni etc), which can create strong recombination centres; and light elements (such as O, C and N), which may create defects that cause recombination or shunting. Crystal defects such as grain boundaries and dislocations also play an important role, and can interact with the impurities, for example, by acting as preferred sites for precipitation of metals.

Even in prime quality monocrystalline wafers, intrinsic defects such as vacancies and self-intersitials, through their interactions with ever-present light lelements such as O and N, can play a critical role in limiting cell performance, especially for high efficiency cell designs that are very sensitive to recombination.

Research Topics


Defects and impurities in solar-grade silicon and multicrystalline silicon wafers:

  • The effect of transition metal impurities such as Fe, Cr, Ni and Cu on solar cell performance.
  • Studying the relative recombination activity of dissolved or precipitated metals.
  • Removal, or 'gettering', of metallic impurities such as Fe by heavily doped surface diffusions.
  • Studying the impact of hydrogenation on dissolved and precipitated metals, and on crystal defects such as dislocations and grain boundaries.

Growth-related defects in high quality monocrystalline silicon wafers:

  • Understanding the structure and evolution of the boron-oxygen defect, also in relation to compensated silicon wafers.
  • Studying the interaction of trace metal impurities with extended defects such as oxygen precipitates and dislocations.
  • Understanding the impact of intrinsic defects related to silicon vacancies and self-interstitials, and their interactions with light elements such as O and N, in high quality Czochralski-grown silicon, especially n-type wafers.

Developing novel techniques for silicon materials characterisation:

  • Development of sensitive, spatially resolved methods for detecting dopants and impurities in silicon wafers based on photoluminescence imaging. (See images at right for examples of PL-based high resolution interstitial iron, dopant, and boron-oxygen defect imaging in silicon wafers.)
  • The use of spectral photoluminescence to study defects and impurities in silicon wafers, such as dislocations, through sub-band-gap luminescence.

Fundamental materials properties:

  • The effects of dopant compensation (the simultaneous presence of p-type and n-type dopants) on carrier recombination and mobilities.
  • The relative impact of defects and impurities in n- and p-type silicon.
  • Fundamental properties of silicon such as Auger recombination, radiative recombination, and band-to-band absorption.

Current research projects


ARENA Project RND009 - Lowering the cost of high efficiency silicon solar panels


Publications

Please visit our group's publications webpage for a full list of our journal and conference publications, many of which can be downloaded as pdf files.

Group Members

Academics

Assoc Prof Daniel Macdonald
Dr Fiacre Rougieux
Dr Sieu Pheng Phang
Anyao Liu

PhD students

Hang Sio
Peiting Zheng
Hieu Nguyen
Chang Sun
Mohsen Goodarzi

Prospective students

Interested in doing a PhD in our group? If you are an Australian or New Zealand citizen or permanent resident, and have a first class honours degree in Engineering or Physics, we may have a project that suits you. For international students, you will need outstanding undergraduate marks in order to be competitive for a scholarship at ANU. Please contact one of the academics listed above for more details.

Collaborators


The Institute for Solar Energy Research Hameln (ISFH, Germany)
The Energy Research Centre of the Netherlands (ECN)
The Fraunhofer Institute for Solar Energy Systems (Fh-ISE, Germany)
The University of New South Wales (UNSW)
BT Imaging
Apollon Solar
Sinton Instruments

10cm wide section of image of interstitial Fe concentration in a multicrystalline silicon wafer.

High resolution image of the interstitial Fe concentration in a multicrystalline silicon wafer (10cm wide section). From A. Liu et al., Progress in Photovoltaics, 19 (6), pp. 649-657, (2011). Click on image for larger version with scale bar.

Image of dopant density variations in a boron-doped, float-zone, 4 inch diameter silicon wafer.

Image of dopant density variations in a boron-doped, float-zone, 4 inch diameter silicon wafer. From S. Y Lim et al., IEEE Journal of Photovoltaics, 3 (2), pp. 649-655 (2013). Click on image for larger version with scale bar.

Time evolution of the boron-oxygen defect density in a p-type Czochralski silicon wafer under illumination.

Time evolution of the boron-oxygen defect density in a p-type Czochralski silicon wafer under illumination. From S. Y Lim et al., Applied Physics Letters, 103, 092105 (2013). Click on image for larger version with scale bar.

PL-based lifetime images of a multicrystalline silicon wafer before and after applying a de-smearing algorithm that corrects for lateral carrier diffusion.

PL-based lifetime images of a multicrystalline silicon wafer before and after applying a de-smearing algorithm that corrects for lateral carrier diffusion. From S. P. Phang et al., Applied Physics Letters, 103, 192112 (2013). Click on image for larger version with scale bar.

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