Solar Energy

This page is about my Ph.D research on thin-film solar photovoltaics at UNSW.

You can see some information on the now rapidly-expanding solar industry in my page about emissions trading.

Absorption Enhancement in Thin-Film Polycrystalline-Silicon Photovoltaic Modules (Ph.D thesis, 1996)

University of New South Wales (Sydney, Australia)

Thank you to the Royal Society, UK, for the Rutherford Scholarship that supported me to do this PhD (during which I sat next to the "Sun King" in the PV Centre led by Professor Martin Green), which was described as “the best PhD I've ever seen” by my supervisor, Dr Stuart Wenham, who was awarded the 1999 Australia Prize.
Also thank you to the Australian Research Council for my subsequent research fellowship award (which ironically was approved by Tony Abbott before he went on to develop a pathological hatred of renewable energy!).

Here is a list of my publications up to Sep. 1998 (when I left the field).  Some of them, including my Ph.D and modelling programs, can be accessed via the links below.

More recently (2018-) I rebooted my ray-tracing programs to look at some new textures for roof-integrated modules — results to come, eventually...

Following is a brief summary of my Ph.D research (a career path I decided to follow when still at school in the 1980s, because I was concerned about the little-recognised greenhouse effect already predicted then — accurately as it turned out):

• Modelling of anti-reflection and light-trapping properties of thin silicon films deposited "conformally" on macro-textured substrates (with texture size or "period" > film thickness).

• Uses ray-tracing of average year-round illumination and includes anti-reflection coatings for the top glass surface as well as the silicon-encapsulation surface (and a rear cell reflector).

• The anti-reflection and light trapping properties are superior to that calculated for a realistic micro-texture, which is modelled using a new kind of ray-tracing program.

• A low shading-loss contacting scheme for thin-film (or conventional wafer) silicon solar photovoltaic (PV) modules is also proposed.

• Conclusions:

  • Conformal films on small-sized inverted tetrahedra (triangular based pyramids with dimensions of around 10-50 microns for a film thickness of 1-3 microns) can produce light trapping that is better than a fully randomising "lambertian" scheme, even under isotropic illumination (which was previously considered to be a theoretical limit).

  • From a practical perspective, the best texture is probably "perpendicular grooves", consisting of conformal silicon films on macro-sized grooves oriented perpendicular to North-South grooves on the top glass/encapsulation surface (running downhill to assist rain cleaning), along with an additional mild micro-texture on the front or rear silicon surface.  This offers lower series resistance for current flowing along the silicon grooves towards contacts, compared to a 3D texture.

Since doing my PhD, the solar industry has developed to the point where conventional crystalline-silicon solar cell technology has reached such low costs and high efficiencies that I no longer think the "conformal film textures" I modelled would enable thin-film polycrystalline-silicon solar cells to become commercially viable, but these textures could potentially improve the performance of thin-film versions of rapidly-improving perovskite-silicon tandem cells, or maybe even triple-junction thin-film cells like perovskite—silicon—silicon-germanium.  In fact, 12.8% efficient perovskite cells are already being made on 1.6 μm wide V-shaped micro-grooves embossed in a flexible, lightweight PET substrate in low-cost "roll-to-roll" manufacturing.

Publications and ray-tracing software

• UNSW Ph.D thesis (1996): "Absorption Enhancement in Thin-Film Polycrystalline-Silicon Photovoltaic Modules"
  (https://doi.org/10.26190/unsworks/4588 or original chapters with colour graphs in PhD zip file download)

• Pascal ray-tracing programs (source code zip file download)

• ‘Conformal Films for Light Trapping in Thin Silicon Solar Cells’ (1996) — as published and pre-print version with colour graphs

• ‘Absorption Enhancement in Conformally Textured Thin-Film Silicon Solar Cells’ (1996) — modelling of 3D textures, including inverted tetrahedra

• ‘Ray-Tracing of Arbitrary Surface Textures for Light-Trapping in Thin Silicon Solar Cells’ (1996-7)

• ‘Methods of Contacting Multijunction Silicon Photovoltaic Modules’ (1997)

• ‘A Low-Temperature Deposited-Silicon Selective-Emitter-Wrap-Through Silicon Solar Cell’ (1998)