Upload
lamnhi
View
220
Download
0
Embed Size (px)
Citation preview
Perovskite solar cellsPresent scenario and future prospects
ANURADHA ASHOK Ph .D
PSG Institute of Advanced Studies
A perovskite solar cell is a type of solar
cell which includes a perovskite structured
compound, most commonly a hybrid
organic-inorganic lead or tin-halide based
material, as the light-harvesting active
layer. Perovskite materials such
as methylammonium lead halides are cheap
to produce and simple to manufacture.
What is a perovskite solar cell?
19 Aug 2016 SOLAR SEMINAR-PSG IAS 2
Web of Science search for “hybrid perovskite OR MAPI OR CH3NH3PbI3 solar cell”
Perovskite solar cells
Efficiency as reported in 2016: 20.1%
19 Aug 2016 SOLAR SEMINAR-PSG IAS 3
Perovskite materials
Usually have stoichiometry ABX3
X is an oxide or halide anion such as Cl, Br and I.
B refers to a metal cation with a coordination number of 6.
The BX6 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 earth metals.
B
19 Aug 2016 SOLAR SEMINAR-PSG IAS 4
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 commonly used material 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
JACS, 136, 622, 2014Methylammonium (MA)
519 Aug 2016 SOLAR SEMINAR-PSG IAS
Organic-Inprganic Hybrid perovskites
19 Aug 2016 SOLAR SEMINAR-PSG IAS 7
Variation in band structure according to molecular orientation
(111)(011)
(111) (011)
Motta et al, Nature communications, DOI: 10.1038/ncomms8026
19 Aug 2016 SOLAR SEMINAR-PSG IAS 8
Methyl ammonium lead iodide-MAPI (CH3NH3PbI3)
Semiconducting material with direct bandgap 1.55eVAbsorption onset 800nmGood light absorber in the whole visible solar emission
spectrum
Weak binding energy of Excitons produced by light absorption ~ 0.030 eVMost of the excitons dissociate rapidly into electrons and
holes at room temperature
Small effective mass with high carrier mobility
Recombination time hundreds of nanoseconds Longer carrier diffusion lengths (100-1000nm) before they
recombine Michael Grätzel , Nature materials vol 13, 2014
19 Aug 2016 SOLAR SEMINAR-PSG IAS 9
Evolution of Perovskite solar cells
Incorporation of MAPI in liquid based DSSCs as a sensitizer improved the power conversion efficiency significantly (3.8%). Poor device stability due to rapid dissolution of the perovskite in the organic solvent
Liquid electrolyte replaced by solid state hole conductor (HTM) CsSnI3-xFx or spiro-MeOTAD
Michael Grätzel , Nature materials vol 13, 2014
19 Aug 2016 SOLAR SEMINAR-PSG IAS 10
Evolution of Perovskite solar cells
Mesoporous TiO2 replaced by Al2O3, electrons percolate alomg the surface of alumina NPs through ultrathin MAPI coating—efficiency -5%
MAPI can also act as hole conductor no need of additional HTM TiO2 scaffold is fully infiltrated with the perovskite light harvesterreduction in thickness and efficiency-12%
Michael Grätzel , Nature materials vol 13, 2014
19 Aug 2016 SOLAR SEMINAR-PSG IAS
1. High efficiency; with an efficiency of 20% after only several years work.
2. Facile low temperature solution-based fabrication method.
3. High absorption coefficient.
4. High diffusion length, high charge-carrier mobilities.
it means that the light-generated electrons and holes can move large
enough distances to be extracted as current, instead of losing their energy
as heat within the cell
5. very high values of open-circuit voltages (VOC) typically obtained.
12
Advantages of Perovskite solar cells
19 Aug 2016 SOLAR SEMINAR-PSG IAS 13
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
Optical properties
19 Aug 2016 SOLAR SEMINAR-PSG IAS 14
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
SmallVolume 11, Issue 1, pages 10-25, 30 OCT 2014 DOI: 10.1002/smll.201402767http://onlinelibrary.wiley.com/doi/10.1002/smll.201402767/full#smll201402767-fig-0002
FA: formamidinium HC(NH2)2+
Band gap tuning
19 Aug 2016 SOLAR SEMINAR-PSG IAS 15
Energy levels for different materials acting as electron transporting material (left), absorbers (middle) and hole transporting materials (right) in solar cells.
Journal of materials chemistry A, DOI: 10.1039/C5TA00873E
Device fabrication based on energy levels
Pablo et al Materials Today Volume 17, Number 1
19 Aug 2016 SOLAR SEMINAR-PSG IAS 16
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
SmallVolume 11, Issue 1, pages 10-25, 30 OCT 2014 DOI: 10.1002/smll.201402767http://onlinelibrary.wiley.com/doi/10.1002/smll.201402767/full#smll201402767-fig-0004
Device structure
19 Aug 2016 SOLAR SEMINAR-PSG IAS 17
Pablo et al, Journal of Physical Chemistry Letters DOI: 10.1021/jz502547f, February 2015
Beyond MAPI
19 Aug 2016 SOLAR SEMINAR-PSG IAS 18
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
SmallVolume 11, Issue 1, pages 10-25, 30 OCT 2014 DOI: 10.1002/smll.201402767http://onlinelibrary.wiley.com/doi/10.1002/smll.201402767/full#smll201402767-fig-0005
Preparation method
19 Aug 2016 SOLAR SEMINAR-PSG IAS 19
One-StepSequential Deposition
Dual-Source Vapor Deposition
Vapor-Assisted Solution Process
Peng Gao Energy Environ. Sci., 2014, 7,2448
Other deposition methods
19 Aug 2016 SOLAR SEMINAR-PSG IAS 20
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.
Highlights
19 Aug 2016 SOLAR SEMINAR-PSG IAS
Niu et al, J. Mater. Chem. A, 2015,3, 8970-8980
CH3NH3PbI3 (s) ↔ PbI2 (s) + CH3NH3I (aq)
CH3NH3I (aq) ↔ CH3NH2 (aq) + HI (aq)
4HI (aq) + O2 (g) ↔ 2I2 (s) + 2H2O (l)
2HI (aq) ↔ H2 (g) + I2 (s)
21
Degrades instantaneouly when measured under ambient conditions due to reaction with oxygen, moisture and UV light
Stability issues
19 Aug 2016 SOLAR SEMINAR-PSG IAS 22
Shin et al, ACS Nano, 2013, 7 (2), pp 1027–1035Kim, et al, ChemSusChem 2013, 6, 449 – 454
Inorganic perovskites
Inorganic perovskites for solar cells
19 Aug 2016 SOLAR SEMINAR-PSG IAS 23
Perovskite and silicon heterojunction solar cells
APPLIED PHYSICS LETTERS 106, 013506 (2015)
Efficiency 24.1%
19 Aug 2016 SOLAR SEMINAR-PSG IAS 25
• Perovskite stack is printed on top of conventional silicon PV cells•Will add 3–5% absolute cell efficiency•Is easily integrated into existing PV manufacturing lines•Adds minimal additional cost
Expected efficiency > 28%
Tandem solar cells
19 Aug 2016 SOLAR SEMINAR-PSG IAS 27
Improving efficiency to exceed thin film 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?
Future challenges for PSCs