Perovskite Solar Cells

Click here to load reader

  • date post

    23-Aug-2014
  • Category

    Science

  • view

    2.053
  • download

    12

Embed Size (px)

description

This presentation summarizes history and recent development of perovskite solar cells. If you have any questions or comments, you can reach me at [email protected]

Transcript of Perovskite Solar Cells

  • All rights reserved. 2014, Wenchun Feng Perovskite Solar Cells Wenchun Feng Garfunkel Group Department of Chemistry and Chemical Biology Rutgers University 3/7/2014 Image credit: B. Zhang, W.C.L. Glenn & M. Liu. If you have any questions or comments, please email (agassifeng at gmail.com).
  • All rights reserved. 2014, Wenchun Feng Schematic 2 Perovskite Precursor Solution CH3NH3I PbI2 fluorine-doped tin oxide substrate spin coat then annealFTO FTO TiO2 FTO TiO2 Perovskite spin coat perovskite then anneal spin coat spiro-OMeTAD FTO TiO2 Perovskite spiro-OMeTAD FTO TiO2 Perovskite spiro-OMeTAD Electrode Deposition leave in air to dope via oxidation Au Au Au -3.9 -5.4 -4.0 -5.2 -5.1 hv - + - + + E (eV) LUMO HOMO CB TiO2 (CH3NH3)PbI3 spiro-OMeTAD Au HOMO Adv. Funct. Mater. 2014, 24, 151. Sci. Rep. 2012, 2. DOI: 10.1038/srep00591. Image Credit: M.B. Johnston (CH3NH3)PbI3
  • All rights reserved. 2014, Wenchun Feng Perovskite Solar Cells Made Simply C&EN Video 3 For a C&EN video, please see https://www.youtube.com/watch?v=oQ2bz6jlbz0
  • All rights reserved. 2014, Wenchun Feng Perovskite Solar Cell is the Poster Child for Solar Energy Conversion Source: Web of Science 4 Henry Snaith
  • All rights reserved. 2014, Wenchun Feng 5
  • All rights reserved. 2014, Wenchun Feng Science. 2013, 342, 794 Chem. Mater. 1999, 11, 3028 Science. 1999, 286, 945 J. Chem. Soc., Dalton Trans., 2001, 1, 1 In the late 1990s, David Mitzi (IBM) made TFT and LED with organometal halide perovskites. In general, Good light emitters = Good light absorbers = Potentially Good PV materials. However, due to its instability, he didnt pursue them as viable PV material. OPV DSSC CIGS 6
  • All rights reserved. 2014, Wenchun Feng What is Perovskite? A perovskite structure is any material with the same type of crystal structure as calcium titanium oxide (CaTiO3), known as the perovskite structure ABX3. First discovered by Gustav Rose in 1839 and named after Russian mineralogist L. A. Perovski. 7
  • All rights reserved. 2014, Wenchun Feng CH3NH3PbX methylammonium lead halide Nature. 2013, 12, 1087 J. Mater. Chem. A, 2013, 1, 15628 Phase Transition (CH3NH3PbI3): Orthorhombic Tetragonal Cubic 162 K 327 K (54 C) The organic ligand is disordered in Tetragonal and Cubic phase. 8
  • All rights reserved. 2014, Wenchun Feng 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 9
  • All rights reserved. 2014, Wenchun Feng 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 10
  • All rights reserved. 2014, Wenchun Feng Crystallinity Tetragonal Structure Lattice Parameters: a = 8.825 , b = 8.835 , c = 11.24 . Science. 2012, 338, 643. 11
  • All rights reserved. 2014, Wenchun Feng 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. 12
  • All rights reserved. 2014, Wenchun Feng Remaining Question: Is the Solar Cell Excitonic? Similar electron and hole diffusion lengths (130 nm and 100 nm in average), either indicate similar mobilities for both electrons and holes, or indicate that the predominant diffusion species is the weakly bound exciton. Based on the work so far, we cannot tell whether the photoexcited species are excitons or free charges Conventional Solar Cell (p-n junction Si) Excitonic Solar Cell (DSSC, OPV) + - + - + - + - interface exciton free charges hv hv J. Phys. Chem. B 2003, 107, 4688 Science. 2013, 342, 341 Science. 2013, 342, 344 13
  • All rights reserved. 2014, Wenchun Feng Carrier Mobility High carrier mobility is important: Because, coupled with high charge carrier lifetimes, it allows for the light- generated carriers move large enough distances to be extracted as current, instead of energy loss by recombination. Inorg. Chem. 2013, 52, 9019 Science. 2013, 342, 317 Adv. Funct. Mater. 2005,15, 77 Combining resistivity and Hall effect data, the electron mobility was calculated to be ~ 66 cm2/Vs for CH3NH3PbI3. This is remarkably high (in comparison, PCBM, a common electron acceptor in OPV, has electron mobility of 0.21 cm2/Vs) 14
  • All rights reserved. 2014, Wenchun Feng High Voc Perovskite solar cells are quite effective in generating a high electric voltage, which is represented by a high open circuit voltage (Voc): CH3NH3PbI2Cl: optical bandgap of 1.55 eV Voc of 1.1 V A voltage drop of only 0.45 eV, competitive with the best thin-film technologies (CIGS: 1.15 eV 0.7 V; Si: 1.1 eV 0.7 V) Compares favorably to DSSC or OPV, which has a larger 0.7-0.8 V voltage drop, resulting in a small portion of the bandgap being extracted as Voc. Other optimization predictions: Higher FF is possible (60-70% over 80%), current can also be higher. Science. 2013, 342, 794 Science. 2012, 338, 643 15
  • All rights reserved. 2014, Wenchun Feng Getting the Best of Both Worlds It has been agreed on that the organic-inorganic hybrid nature is what makes it so successful: The organic component renders good solubility to the perovskite and facilitates self-assembly, effectively enabling its precipitation/deposition from solution. The inorganic component produces an extended network by covalent and/or ionic interactions (instead of weaker forces such as Van der Waals or - interactions). Such strong interaction allows for precise crystalline structure in the deposited films. Nature. 2013, 12, 1087 16
  • All rights reserved. 2014, Wenchun Feng DSSC: Predecessor to Perovskite Solar Cells Current Perovskite Solar Cells are built upon the architectural basis for DSSCs Pioneering work by Grtzel (EPFL, Switzerland) that has garnered ~ 17000 citations Nature. 1991, 353, 737 www.sigmaaldrich.com technical documents 17
  • All rights reserved. 2014, Wenchun Feng Replacing Dye with Perovskite Dyes do not absorb all the incident light, reducing DSSC efficiency. In 2009, Miyasaka (Toin U. of Yokohama, Japan) turns to perovskite as possible replacement of the dye and achieved 3.8% efficiency. Problem: Liquid electrolyte dissolved away the perovskite within minutes. Liquid Electrolyte 0.15 M LiI and 0.075 M I2 in methoxyacetonitrile JACS. 2009, 131, 6050. 18
  • All rights reserved. 2014, Wenchun Feng Replace Liquid Electrolyte with a Solid Hole Transporting Layer (HTL) 2012, Nam-Gyu Park (Sungkyunkwan U., South Korea) teamed up with Grtzel, over 9% efficiency. HTL layer: spiro-OMeTAD Sci. Rep. 2012, 2, DOI: 10.1038/srep00591 19
  • All rights reserved. 2014, Wenchun Feng TiO2 Al2O3 Scaffold and Single Layer 2012, Henry Snaith (Oxford U.): Is TiO2 essential for high efficiency? Switched to an insulating Al2O3 scaffold, expected to see a decrease in efficiency. Surprisingly, the device with Al2O3 has a higher efficiency than that with TiO2 (11% vs. 7.6%). If all that Al2O3 does is scaffolding, what if we get rid of it as well? 2013 15 % Al2O3 solution vacuum deposition Perovskite Precursor Solution CH3NH3I PbI2 2013 11 % Science. 2012, 338, 643. Nature. 2013, 501, 395. Adv. Funct. Mater. 2014, 24, 151 Do not need artificial interfaces for efficient charge separaton! These two results are remarkable, in that they prove that these perovskites work as conventional semiconductors (Si, GaAs, etc). single layer (thin film) device 20
  • All rights reserved. 2014, Wenchun Feng Sequential Deposition 2013, Grtzel sticks with the TiO2 structure and tinkered with the deposition step. mesoporous TiO2 PbI2 CH3NH3I Efficiency: 15% Nature. 2013, 499, 316 perovskite 21
  • All rig