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.

1. Perovskites-based Solar Cells
The challenge of material choice for p-i-n perovskites thin-Film PV
Akinola Oyedele

2. 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

3. Introduction-Why Solar?
Hydro
Sun
Fossil
Wind
Tidal
PV
Bio-fuels

4. Solar-Current State-of-the-Art Tech.
Image Credit: NREL, 2014

5. Solar-Current State-of-the-Art Tech.
Image Credit: Ossila

6. Solar-Current State-of-the-Art Tech.
Image Credit: G. Conibeer, 2007 Third-generation photovoltaics Material Today 10 11 44 50

7. Perovskite crystal
The Perovskite Material
• What is Perovskite?
• Basic Structure
• Other applications
• The organometal halide perovskite
Lev Perovski
http://en.wikipedia.org/wiki/Lev_Perovski
(Kim, Im, & Park, 2014) (Bisquert, 2013)

8. Perovskite crystal
The Perovskite Material
Peng Gao Energy Environ. Sci., 2014, 7,2448

9. Structural Properties
• Highly crystalline structure (depends on mixed halide, annealing,
processing)
• Size of crystallite
• Crystallographic changes with temperature
C. C. W. Chen, Adv. Mater. 2014, 26, 6647–6652 W. Chen, Adv. Mater. 2014, 26, 6647–6652

10. Optical Properties
• High absorption coefficient
• Optical absorption as a function of the metal halide
• Band- tuning
M. A. Green, N Peng Gao Energy Environ. Sci., 2014, 7,2448 ature Photonics 8, 50-514 (2014)

11. 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
퐶 =
푘휀0휀푟퐴
푑
Image Credit: solarwiki.ucdavis.edu

12. Evolution of Perovskite Solar Cells
A. Hagfeldt, Chem. Rev. 2010, 110, 6595–6663
(Snaith H. J., 2013)
Dye-Sensitized Solar Cell

13. 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
Aluminium
TiOx
[60]PCBM
Perovskite
PEDOT:PSS
FTO
P. Decampo, Nature Comm4, 2761 (2013) SEM Image

14. The P-I-N Device Structure
p
i
n
Image Credit: Foozieh Sohrabi

15. Material Choice (1) - Transporters
• Charge carrier selectivity
• Matching of energy levels
• Degree of chemical interaction
• Conductivity
• Light absorption

16. 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)

17. Design Consideration
A B C

18. Component Thickness
Architecture 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

19. Deposition Methods
One-Step
Sequential Deposition
Dual-Source
Vapor Deposition
Vapor-Assisted Solution Process
Peng Gao Energy Environ. Sci., 2014, 7,2448

20. 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)

22. Questions

23. 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.