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

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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.