PERVOSKITES SOLAR CELL

1. Perovskite Solar Cells
New Promising Materials for Next Generation Solar Cells
Abhishek Ranjan
BATCH 11,
ISP, CUSAT
20-10-2016
Slides available at- www.abhishekranjan.work

2. OVERVIEW
• Basics of Solar cell
• Emergence of Pervoskites .
• Features of Solar cell.
• Structure of Pervoskites
• Preparation of Pervoskites solar cells
• Future Challenges
• References
2

3. Basic Structure of a Photovoltaic Solar Cell
• A photovoltaic solar cell is made of three main part:
• Light Absorber; converting incident photons to electron and holes
• Carrier Collector/s; capturing the carriers (electron and holes)
• Metal Contacts: transferring the carriers to the circuit
• The heart of a solar cell is the absorber layer
3Basic schematic of a photovoltaic solar cell

4. Three Generations of Solar Cells
• Wafer based:
• Monocrystalline silicon 25%
• Polycrystalline silicon 20%
• Multi-junction cell (different band-gap materials) 40%
• Thin Films:
• Amorphous thin film silicon 13%
• CdTe (Cadmium Telluride) 17%
• CIGS (Copper Indium Gallium Selenium) 20%
• Low Cost and high Efficient:
• DSSC (Dye-sensitized solar cells)
• QDSSC (Quantum Dot-sensitized solar cells)
• OPV (Organic photovoltics)
• QDs-Polymer Hybrid solar cells
• Perovskite Solar Cells
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Highest efficiency

5. Emergence of Perovskite Solar Cells
• Efficiency jump in photovoltaics research
• From 3.8 % in 2009 to 15.9 % in 2014
5Science 18 October 2013: Vol. 342 no. 6156 pp. 317-318
15% perovskite solar cell made in University of Oxford

6. Material Properties:
Good for Photovoltaics, but with Caution
• Cheap Manufacturing:
• Lower manufacturing costs expected: directly deposited from solution
• Caution: Encapsulation needed, which may increase cost
• Material Properties for High Efficiency Photovoltaics:
• 1. High Optical Absorption Coefficient
• 2. Excellent Charge Carrier Transport (crystallinity, diffusion length, carrier mobility)
• 3. Promising Device Parameter: High Voc of >1.1 V is reported
• Stability:
• Study shows it can maintain more than 80% of its initial efficiency after 500 hours.
• Caution: More studies needed. Lifetime of 15 years has not been demonstrated.
The ultimate goal of 15-year-lifetime not demonstrated.
• Other Real World Concerns (equally important but omitted here):
• Toxicity from Pb
• Scaling Problem
Nature. 2013, 12, 1087
Nature Comm. 2013, DOI: 10.1038/ncomms3885
Science. 2013, 342, 317
Nature. 2013, 499, 316
6

7. High Optical Absorption
Coefficient
• Perovskite Absorption Coefficient: 1.5X104 cm-1 at 550 nm, which
is one order of magnitude higher than conventional ruthenium-
based organometallic N719 dye
Nanoscale, 2011, 3, 4088

8. Carrier Diffusion Length
quartz
CH3NH3PbI3
PCBM
quartz
CH3NH3PbI3
Spiro-OMeTAD
electron-extracting layer hole-extracting layer
Science. 2013, 342, 341
Science. 2013, 342, 344
e h
PL quenching originates from the charge-carrier
extraction across the interface.
8

9. Crystallinity
Tetragonal Structure
Lattice Parameters:
a = 8.825 Å, b = 8.835 Å, c = 11.24 Å.
Science. 2012, 338, 643.
9

10. Perovskite Crystal Structure
• Usually have stoichiometry of AMX3
• X is an oxide or halide anion such as Cl, Br and I.
• M refers to a metal cation with a coordination number of 6.
• The MX6 octahedra share corners and A is usually a large cation
that fills the cuboctahedral holes with coordination number of
12.
• A can be Ca, K, Na, Pb, Sr, other rare metals.
10CrystEngComm, 2010, 12, 2646-2662

11. Organic–inorganic Hybrid Perovskites
• First three-dimensional organic–inorganic hybrid perovskite,
discovered by replacing caesium in CsPbX3 (X = Cl, Br or I)
with methylammonium cations (MA = CH3NH3
+) by Dieter
Weber, in 1978.
• CH3NH3PbI3 is most common used materials for making high
efficiency perovskite solar cells.
• CH3NH3PbI3 is a semiconducting pigment with a direct bandgap
of 1.55 eV with absorption coefficient as high as 104–105 cm−1
11JACS, 136, 622, 2014
Methylammonium (MA)

12. Band Gap Tuning
• This field is also known as molecular enginnering.
• Bandgap tuning is required to extend the absorption to longer
wavelengths without sacrificing the absorption coefficient.
• Changing in any of A, M and X in AMX3 changes the bandgap.
• The bandgap also can be tuned in between 1.55 eV and 1.17 eV
by varying the ratio of lead to tin.
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13. Device structure
• The device structure, related materials, and interfacial
modification are key factors in performance of solar cells.
• Two typical structures can be constructed: a) mesoscopic
nanostructure and b) planar structure.
• Mesoporous TiO2 layer usually is used to collect the electrons
• Organic Hole transporting material (HTM) collects the holes
• Planar structure has simpler structure and higher efficiency
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14. Preparation Method
• There are two common methods:
1) one step coating: spin-coating a mixed CH3NH3I and PbI2solution
2) two-step coating: spin-coating CH3NH3I after coating with PbI2
14
Small
Volume 11, Issue 1, pages 10-25, 30 OCT 2014 DOI: 10.1002/smll.201402767
http://onlinelibrary.wiley.com/doi/10.1002/smll.201402767/full#smll201402767-fig-0005

15. Preparation Method cont.
• All deposition process happens at a low temperature (below 150
°C), which is suitable for the fabrication of flexible solar cells
based on PET substrates.
• The concentration of the CH3NH3I solution affects the crystal
size from about 90 nm to about 700 nm.
• Photovoltaic performance was strongly influenced by the
CH3NH3I concentration, i.e., the crystal size of CH3NH3PbI3
• CH3NH3PbI3 degrades in humid conditions and forms PbI2 at
higher temperatures due to the loss of CH3NH3I
• Lead (Pb) compounds are very toxic and harmful to the
environment.
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16. Future Challenges of Perovskite Solar Cells
• Improving efficiency to exceed thin film CdTe solar cells
• By understanding their material properties and optimal cell designs
• Increasing air and temperature stability
• Replacing toxic Pb with a greener element
• Is AMX3 (perovskite structure) the best stoichiometry? Have we
tried other structures?
• Life time of more than 15 years have not been seen.
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17. References
1. Small, Volume 11, Issue 1, pages 10-25, 30 OCT 2014 DOI: 10.1002/smll.201402767
2. Nature Materials 13, 838–842 (2014) doi:10.1038/nmat4065
3. Science 18 October 2013: Vol. 342 no. 6156 pp. 317-318
4. CrystEngComm, 2010, 12, 2646-2662 10.1039/C001929A
5. PHYSICAL REVIEW B 90, 045207 (2014)
6. Nature Photonics 8, 506–514 (2014) doi:10.1038/nphoton.2014.134
7. Angewandte Chemie International Edition Volume 53, Issue 11, pages 2812–2824, March
10, 2014
8. Phys. Rev. B 90, 045207 – Published 24 July 2014
9. Wikipedia
10. Solar Energy International Magazine
11. Phys.org
12. Pervoskite.info
13. Science Channel
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