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Perovskite-based PV have triggered widespread interest in the scientific community because these materials offer the attractive combinations of low cost and theoretically high efficiency. However, several challenges must be overcome for these relatively new PV materials. Among the many important challenges, one is the choice of materials to be used in thin film PV devices.. Based on fundamental principles of solar photovoltaics, this problem focuses on two aspects of the perovskite system: 1) Based on a planar p-i-n device structure, a potential list of p- and n-type charge collecting layers as well as the conductive contacts that could be used with a promising perovskite absorber material was identified, and a proper justification for the selection of each material in the device was given. 2) Three theoretical p-i-n type solar cells were made with the chosen materials and appropriate conductive contacts.
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Perovskites-based Solar Cells
The challenge of material choice for p-i-n perovskites thin-Film PV
Akinola Oyedele
Outline
• Introduction• Background of Perovskites• Evolution of Perovskites• The p-i-n Perovskite Structure• Factors to Consider in Material Choice• Selected Materials• Design Consideration • Conclusion
Image Credit: solarsenergyprosandcons.com
Image credit: www.gatescambridge.org
Introduction-Why Solar?
Sun
HydroFossil
WindTidal
Bio-fuels
PV
Solar-Current State-of-the-Art Tech.
Image Credit: NREL, 2014
Solar-Current State-of-the-Art Tech.
Image Credit: Ossila
Solar-Current State-of-the-Art Tech.
Image Credit: G. Conibeer, 2007 Third-generation photovoltaics Material Today 10 11 44 50
Perovskite crystal
The Perovskite Material
• What is Perovskite? • Basic Structure• Other applications• The organometal halide perovskite
http://en.wikipedia.org/wiki/Lev_Perovski
Lev Perovski
(Bisquert, 2013) (Kim, Im, & Park, 2014)
Perovskite crystal
The Perovskite Material
Peng Gao Energy Environ. Sci., 2014, 7,2448
Structural Properties
• Highly crystalline structure (depends on mixed halide, annealing, processing)
• Size of crystallite• Crystallographic changes with temperature
C. W. Chen, Adv. Mater. 2014, 26, 6647–6652 C. W. Chen, Adv. Mater. 2014, 26, 6647–6652
Optical Properties
• High absorption coefficient• Optical absorption as a function of the metal halide • Band- tuning
M. A. Green, Nature Photonics 8, 50-514 (2014) Peng Gao Energy Environ. Sci., 2014, 7,2448
Electronic Properties
• Large Bohr radius Wannier-type excitons• Low binding energies• High dielectric constant • Allow for Charge accumulation • Ambivalent charge transport• Very high e- h+ diffusion lengths
𝐶=𝑘𝜀0 𝜀𝑟 𝐴
𝑑Image Credit: solarwiki.ucdavis.edu
Evolution of Perovskite Solar Cells
A. Hagfeldt, Chem. Rev. 2010, 110, 6595–6663
(Snaith H. J., 2013)
Dye-Sensitized Solar Cell
Achieving ɳ > 20% for Planar p-i-n Perovskites• Improve homogeneity • Narrow band-gap • Multijunction and tandem cells• Better materials for p & n layer to increase FF
Solar Spectrum
Image Credit: www.geog.ucsb.edu
TiOx
PEDOT:PSS
FTO
Perovskite
[60]PCBM
Aluminium
SEM ImageP. Decampo, Nature Comm 4, 2761 (2013)
The P-I-N Device Structure
pi
n
Image Credit: Foozieh Sohrabi
Material Choice (1) - Transporters
• Charge carrier selectivity • Matching of energy levels• Degree of chemical interaction• Conductivity• Light absorption
Materials Choice (2) - Contacts
• Light absorption• Work function • Chemical contamination
Back Contact Electrode:
Gold; work function -5.1 eV
Silver; work function -4.26 eV
Aluminum; work function - 4.28 eV
Transparent Conductive Front Contact:
Fluorine-doped tin oxide (FTO); work function: -4.4 eV (Abrusci,
Stranks, Docampo, Yip, Jen, & Snaith, 2013)
Indium tin oxide (ITO); work function: -4.8 eV (Seo, et al., 2014)
Design Consideration
A B C
Component ThicknessArchitecture A Architecture B Architecture C
Glass
700 nm-900 nm
Glass
700 nm-900 nm
Glass
700 nm-900 nm
ITO
550-700 nm
FTO
700 nm
FTO
700 nm
PTAA
60-70 nm
TiO2
50-90 nm
PC61BM
30-50 nm
CH3NH3PbI3-xClx
350-450 nm
CH3NH3PbI3:
250-300 nm
CH3NH3PbI3-xClx
350-450 nm
TiO2
50-90 nm
Spiro-MeOTAD
150-200 nm
Spiro-MeOTAD
150-200 nm
Ag
60 nm
Au
60 nm
Au
60 nm
Total Thickness
1.77- 2.27 μm
Total Thickness
1.91 - 2.25 μm
Total Thickness
1.99 - 2.36μm
Deposition Methods
One-StepSequential Deposition
Dual-Source Vapor Deposition
Vapor-Assisted Solution Process
Peng Gao Energy Environ. Sci., 2014, 7,2448
Conclusion
• Perovskite absorber: polycrystalline, higher abs coeff., & higher carrier LD
• Efficiency of > 20% can be achieved• There is a bright future for perovskites p-i-n solar cells if the problems
relating to stability and toxicity can be addressed • Proposed configurations guarantee better interface layer engineering
and charge transport.
H. Zhou, Science, 345, 542(2014)
Questions
Selected References
• Boix, P. P., Nonomura, K., Mathews, N., & Mhaisalkar, S. G. (2014). Current progress and future perspectives for organic/inorganic perovskite solar cells. Materials Today , 17 (1), 16–23.
• Edri, E., Kirmayer, S., Mukhopadhyay, S., Gartsman, K., Hodes, G., & Cahen, D. (2014). Elucidating the charge carrier separation and working mechanism of CH3NH3PbI3−xClx perovskite solar cells. Nature Communications , 5, 1-8.
• Liu, M., Johnston, M. B., & Snaith, H. J. (2013). Efficient planar heterojunction perovskite solar cells by vapour deposition. Nature , 501, 395.
• Snaith, H. J. (2013). Perovskites: The Emergence of a New Era for Low-Cost, High-Efficiency Solar Cells. Journal of Physical Chemistry Letters (4), 3623-3630.
• Sum, T. C., & Mathews, N. (2014). Advancements in perovskite solar cells: photophysics behind photovoltaics. The Royal Society of Chemistry .
• Tanaka, K., Takahashia, T., Takuma, B., & Kondoa, T. (2003). Comparative study on the excitons in lead-halide-based perovskite-type crystals CH3NH3PbBr3 CH3NH3PbI3. Solid State Communications , 127, 619-623
• Xing, G., Mathews, N., Sun, S., Lim, S. S., Lam, Y. M., Grätzel, M., et al. (2013). Long-range balanced electron- and hole- transport lengths in organic-inorganic CH3NH3PbI3. Science , 342, 344-347
• Yamamuro, N. O., Matsuo, T., & Suga, H. (1992). Dielectric study of CH3NH3PbX3 (X = Cl, Br, I). Journal of Physics and Chemistry of Solids , 53 (7), 935-939.
