NREL_rapid_development_intro
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This document provides an overview of several projects related to disorder in copper zinc tin sulfide (CZTS) for solar cell applications. It discusses: 1. Evidence of disorder within the Cu-Zn sub-lattice of CZTS from neutron diffraction data and Raman spectroscopy measurements. 2. A Monte Carlo model of Cu-Zn disorder in CZTS that shows a plateau of order with respect to temperature, indicating a thermodynamic limit on Cu-Zn order. 3. Next steps in exploring tin disorder in CZTS using the Monte Carlo model, as well as studying the effects of disorder on the electronic band structure and properties of off-stoichiometric CZTS.
![Disorder in Cu-Zn sub-lattice in CZTS
z = ¾
z = ¼
Disorder in z = ¼ and
z = ¾ planes
[Cu-
Zn + Zn+
Cu]](https://image.slidesharecdn.com/rapiddevel21-09-17-170921213508/85/NREL_rapid_development_intro-2-320.jpg)
![Point Defects in CZTS
Chen et al, Physical Review B, 81(24), 245204 (2010)
[Cu-
Zn + Zn+
Cu]
antisite pair
Low energy
defect complex:](https://image.slidesharecdn.com/rapiddevel21-09-17-170921213508/85/NREL_rapid_development_intro-3-320.jpg)
NREL_rapid_development_intro
- 2. Disorder in Cu-Zn sub-lattice in CZTS z = ¾ z = ¼ Disorder in z = ¼ and z = ¾ planes [Cu- Zn + Zn+ Cu]
- 3. Point Defects in CZTS Chen et al, Physical Review B, 81(24), 245204 (2010) [Cu- Zn + Zn+ Cu] antisite pair Low energy defect complex:
- 4. Recent Evidence of Disorder Disorder within Cu-Zn layers from neutron powder diffraction data
- 5. Recent Evidence of Disorder Using Raman intensity as an order parameter, TC= 533 K
- 6. Recent Evidence of Disorder Zn-rich domains in atom probe tomography
- 7. Disorder in Cu-Zn sub-lattice in CZTS Gokmen et al, Appl. Phys. Lett. 103, 103506 (2013)
- 8. CZTS Monte Carlo Cu-Zn disorder model 1. Q order parameter Finite size effects 2) Zn-Zn nearest-neighbour PCF peak = 1, fully ordered = 0, complete disorder Q parameter vs. T https://github.com/WMD-group/Eris PCF peak intensity vs. T
- 9. CZTS Monte Carlo Cu-Zn disorder model Plateau of Cu-Zn order w.r.t T thermodynamic limit on Cu-Zn order at accessible T DOI: 10.1002/pssb.201600372 https://github.com/WMD-group/Eris (currently exploring parameterisation for T-dependence)
- 10. CZTS Monte Carlo Cu-Zn disorder model Next steps? 1. Sn disorder Possible reduction in formation energy with Cu-Zn disorder? 2. Band tailing from distribution of electrostatic potential 3. Disorder in off-stoichiometric CZTS Analyse Sn-Sn PCFs (2D and 3D) https://doi.org/10.1016/j.jallcom.2016.07.298 https://github.com/WMD-group/Eris
- 11. Initial study: Photoferroic minerals for PV? • Enhanced carrier separation from internal E-fields? • Exploitation of APE and BPE? • Photovoltages >> Eg • PV effect in single crystals (without p–n junction) DOI: 10.1039/C7SE00277G • HSE band structures • Direct Eg for enargite and stephanite • Rashba splitting of CBM for bournonite • Absorption coefficients • m*’s • Strength of lattice polarisations • Speculation of defect-tolerance based on VBM bonding character • Literature review: (limited) known predicted and exptl. properties, synthesis proceedures
- 12. 1. Predict suitable device architectures VOC losses linked to misalignment of bands with contact materials Poor epitaxy from lattice mismatch 2. Investigate defect physics of the materials Likely impact of defects on PV performance Predicting and tuning impact? DOI: 10.1039/c7tc01920c Accelerate development of devices!
- 13. Screen by necessary conditions for good contact 1. Electronic matching Optimal band offsets Screen by IP and EA Minimise VOC loss across junction 2. Lattice strain Match crystal lattices Minimal for good epitaxy DOI: 10.1039/c5tc04091d 1. Predictions for device architecture Keith Butler: k.t.butler@bath.ac.uk https://github.com/keeeto/ElectronicLatticeMatch
- 14. 2. Predicting and tuning defect-tolerance? Calculate defect formation energy and transition levels Predict likely concentration of deep vs. shallow defects Tuning chemical potential during synthesis Increase energy for deep defects Look into benign defect complexes Encourage formation of other defects to ‘clean up’ the band gap? DOI: 10.1002/adma.201203146 DOI: 10.1038/nmat.4973
- 15. Bonus slides!
- 16. Cutoff radius for lattice electrostatics summation
- 17. Equilibration
Editor's Notes
- #4: ‘CuZn is the lowest-energy defect at all the points in the stable region, significantly lower than that of VCu and ZnSn, showing that the CuZn antisite is the dominant intrinsic defect in this quaternary kesterite semiconductor’