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“Improving the sustainability of photovoltaic materials” – Dr Patrick Isherwood, Loughborough University

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“Improving the sustainability of photovoltaic materials” – Dr Patrick Isherwood, Loughborough University

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“Improving the sustainability of photovoltaic materials” – Dr Patrick Isherwood, Loughborough University, presenting at the Net Zero Conference 2022, ‘Research Journeys in/to Net Zero: Current and Future Research Leaders in the Midlands, UK’ (on Friday 24th June 2022 at De Montfort University)

“Improving the sustainability of photovoltaic materials” – Dr Patrick Isherwood, Loughborough University, presenting at the Net Zero Conference 2022, ‘Research Journeys in/to Net Zero: Current and Future Research Leaders in the Midlands, UK’ (on Friday 24th June 2022 at De Montfort University)

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“Improving the sustainability of photovoltaic materials” – Dr Patrick Isherwood, Loughborough University

  1. 1. Improving the Sustainability of Photovoltaic Materials Dr. Patrick Isherwood CREST, Wolfson school, Loughborough University
  2. 2. Photovoltaics crash course • What are they? – Silicon – CdTe – CIGS – Organometal halide perovskites – …Others? • Semiconductor-based devices for direct conversion of light into electrical energy • Most common form is silicon p-n junction
  3. 3. Photovoltaics crash course • Why do we care? – Incoming solar resource is about 174 PW – More than 10,000 times humanity’s annual energy usage – Plentiful and effectively infinite clean energy source • But… – Energy is not always available when needed – Dispersed nature makes it more challenging to capture – Although increasingly cost-effective, solar modules are still relatively expensive
  4. 4. Geologist to solar energy researcher • 2004-8: MSci in Geoscience from Durham • 2009-10: MSc in Engineering Geology from Newcastle • 2011-15: PhD in Electrical Engineering from Loughborough So why the change? • Unemployment leaves plenty of time to contemplate your surroundings! • Winter 2010 was particularly cold, and the spring and summer were very warm and green in comparison…
  5. 5. Doctoral research: TCOs and negative results
  6. 6. Transparent conducting oxides • One of those things everyone uses, but no-one has ever heard of! • Used in anything which needs a visually transparent electrical contact • Computer monitors, smartphones, flat-screen TVs, smart windows, double glazing, touchscreens… • Consist of wide bandgap metal oxide semiconductors which are degenerately doped to make them conductive • Materials which combine the highest transparency with the best electrical conductivity are mostly based on indium oxide
  7. 7. TCOs: extracting current • Widely used as front transparent contacts in thin film cells​ • Many experimental devices use fluorine-doped tin oxide coated glass as substrates​ • Vital to the development of next-generation concepts such as tandem and multijunction devices • But… All commercially available examples are n-type
  8. 8. Why p-type transparent conductors? General uses: • High work-function transparent contacts • Transparent electronics Photovoltaic applications: • Tandem and multijunction cell interconnects • Bifacial cells • Back contacts for OPV, CdTe etc. • Hole transport materials for perovskites However, it turns out that there is a problem… THEY DON’T WORK! At least, not very well.
  9. 9. Research problems, new materials and concepts
  10. 10. Photovoltaics materials problems • Silicon is the second most abundant material in the Earth’s crust • Refining process involves reducing SiO2 using carbon • Production of solar grade (very high purity) silicon is very energy- intensive • Alternatives include CdTe, CIGS and organometal halide perovskites • Of these, only CdTe remains commercially viable
  11. 11. Photovoltaics materials problems • CdTe and CIGS both contain rare and toxic elements • High-efficiency devices are usually deposited using high vacuum methods, which are expensive • Room-pressure techniques have been developed, particularly for CIGS, but… https://en.wikipedia.org/wiki/Hydrazine
  12. 12. Photovoltaics materials problems • Alternative solution approach developed at CREST using a combination of a dithiol and a diamine as the solvents • Enables direct dissolution of Cu2S, In2Se3 and Ga. Excess Se and S are also added • Current lab record of 12% • Still involves rare materials, but the process also works for more Earth-abundant technologies
  13. 13. Possible research directions • Development of cheap, Earth-abundant, atmospherically processable and long-term stable absorber materials – Metal-organic complexes (tannates, curcumin complexes, dyes…) – Alternative chalcogen materials (Cu2S, FeS2…) – N-type metal oxide absorbers (Copper tungstate) • Alternative low-energy, low cost and environmentally friendly means for refining of silicon
  14. 14. Photovoltaic modules problems • Installed capacity has been increasing near-exponentially for over a decade • Modules typically have a stated lifetime of 25 years • The number of modules needing to be recycled will increase nearly exponentially within the coming decade!
  15. 15. Photovoltaic modules problems • The recycling problem is mostly economic not technological • All glass, metal and silicon components of a silicon module can theoretically be fully recycled and reused effectively infinitely • All glass, metal and semiconductor components in both CIGS and CdTe can theoretically be recovered, fully recycled and reused • CdTe modules are already almost fully recycled • All modules contain polymeric materials which are not currently recyclable https://www.flickr.com/photos/dullhunk/28251201308 https://doi.org/10.3390/su14031676 https://doi.org/10.3390/su14031676
  16. 16. Possible research directions • Silicon is likely to remain the primary photovoltaic technology for the foreseeable future – Development of low-cost methods for refining high-grade silicon from defunct cells • Technology-agnostic research possibilities: – Glass-glass modules which contain no polymeric materials – Design modules to make them more readily recyclable
  17. 17. Conclusions • Photovoltaic technology, and particularly silicon PV, is an increasingly cheap means for generating electricity • Silicon is abundant, but is energy-intensive to refine • The current alternatives all have problems – rare and/or toxic materials, energy- intensive processing or significant atmospheric instability • Modules are designed to last 25 years or more, making them difficult to dismantle. This is made worse by the widespread use of non-recyclable polymeric materials • Plenty of new materials to research! • May be ways to refine silicon without using carbon • It is theoretically possible to make a glass-backed module containing no polymers • New modules should be designed to be both durable and simple to recycle
  18. 18. Any questions?

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