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Overview of Perovskite Solar Cells

Perovskite Solar CellsNew Promising Materials for Next Generation Solar Cells

Abhishek RanjanBATCH 11, ISP, CUSAT20-10-2016

Slides available at- www.abhishekranjan.work

OVERVIEWBasics of Solar cellEmergence of Pervoskites .Features of Solar cell.Structure of PervoskitesPreparation of Pervoskites solar cellsFuture ChallengesReferences

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Basic Structure of a Photovoltaic Solar CellA photovoltaic solar cell is made of three main part: Light Absorber; converting incident photons to electron and holesCarrier Collector/s; capturing the carriers (electron and holes)Metal Contacts: transferring the carriers to the circuitThe heart of a solar cell is the absorber layer3

Basic schematic of a photovoltaic solar cell

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Three Generations of Solar CellsWafer based: Monocrystalline silicon 25%Polycrystalline silicon 20%Multi-junction cell (different band-gap materials)40%Thin Films:Amorphous thin film silicon13%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 cellsPerovskite Solar Cells

4Highest efficiency

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Emergence of Perovskite Solar CellsEfficiency jump in photovoltaics researchFrom 3.8 % in 2009 to 15.9 % in 2014

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Science 18 October 2013: Vol. 342 no. 6156 pp. 317-318

15% perovskite solar cell made in University of Oxford

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Material Properties: Good for Photovoltaics, but with CautionCheap Manufacturing: Lower manufacturing costs expected: directly deposited from solutionCaution: Encapsulation needed, which may increase cost

Material Properties for High Efficiency Photovoltaics:1. High Optical Absorption Coefficient2. 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 PbScaling ProblemNature. 2013, 12, 1087Nature Comm. 2013, DOI: 10.1038/ncomms3885Science. 2013, 342, 317 Nature. 2013, 499, 3166

a cheap and scalable approach that is also the main strength of alternative technologies such as organic photovoltaics, dye-sensitized solar cells and colloidal quantum dot-based solar cells.

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High Optical Absorption CoefficientPerovskite 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

Carrier Diffusion Length

quartzCH3NH3PbI3PCBMquartzCH3NH3PbI3Spiro-OMeTADelectron-extracting layerhole-extracting layer

Science. 2013, 342, 341Science. 2013, 342, 344e

h

PL quenching originates from the charge-carrier extraction across the interface. 8

By time-resolved transient photoluminescence, 2 papers (published at the same time) claimed extremely high carrier diffusion lengths of > 100 nm. In one of the papers, the mixed halide perovskite has an even longer diffusion length of >1000 nm. charge-carrier extraction model based on diffusion was used to estimate the charge carrier diffusion lengths, obtained minimum estimates of 130 and 90 nm for electrons and holes, respectively. (compared to the only 10 nm for polymers in PV.)8

Crystallinity

Tetragonal Structure

Lattice Parameters:a = 8.825 , b = 8.835 , c = 11.24 . Science. 2012, 338, 643.

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Perovskite Crystal StructureUsually 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.

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CrystEngComm, 2010,12, 2646-2662

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Organicinorganic Hybrid PerovskitesFirst three-dimensional organicinorganic 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 104105cm1

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JACS, 136, 622, 2014

Methylammonium (MA)

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Band Gap TuningThis 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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Device structureThe 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 electronsOrganic Hole transporting material (HTM) collects the holesPlanar structure has simpler structure and higher efficiency13

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Preparation MethodThere are two common methods: one step coating: spin-coating a mixed CH3NH3I and PbI2solution two-step coating: spin-coating CH3NH3I after coating with PbI2

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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

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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 thecrystal size from about 90 nm to about 700 nm.Photovoltaic performance was strongly influenced by the CH3NH3I concentration, i.e., the crystal size of CH3NH3PbI3CH3NH3PbI3degrades in humid conditions and forms PbI2at higher temperatures due to the loss of CH3NH3ILead (Pb) compounds are very toxic and harmful to the environment.15

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Future Challenges of Perovskite Solar CellsImproving efficiency to exceed thin film CdTe solar cellsBy understanding their material properties and optimal cell designsIncreasing air and temperature stabilityReplacing toxic Pb with a greener elementIs 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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ReferencesSmall, Volume 11, Issue 1, pages 10-25, 30 OCT 2014 DOI: 10.1002/smll.201402767Nature Materials 13, 838842 (2014) doi:10.1038/nmat4065Science 18 October 2013: Vol. 342 no. 6156 pp. 317-318CrystEngComm, 2010,12, 2646-2662 10.1039/C001929APHYSICAL REVIEW B 90, 045207 (2014)Nature Photonics 8, 506514 (2014) doi:10.1038/nphoton.2014.134Angewandte Chemie International Edition Volume 53, Issue 11, pages 28122824, March 10, 2014Phys. Rev. B 90, 045207 Published 24 July 2014WikipediaSolar Energy International MagazinePhys.orgPervoskite.infoScience Channel

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