Capturing Energy from the Sun. Solar Cells Solar Thermal Solar Fuels Bioenergy

Capturing Energy from the Sun Solar Cells Solar Thermal Solar Fuels Bioenergy

Installed PV Cost Breakdown a Globally, module prices are between $0.60-0.90/W depending on tariffs In the US, non-module costs represent >75% of the total system costs! Tracking the Sun VI (LBNL report 2013)

35.00 30.00 Global PV Annual Installations (GW) 30.39 31.10 35.00 25.00 20.00 15.00 2003-2009: Silicon Valley Got Frothy 17.06 10.00 5.00 0.00 1970-2002: The Niche Years a 0.20 0.30 0.36 0.47 0.58 1.13 1.41 1.58 6.71 7.38 2.58 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 EPIA.org, Global Outlook for Photovoltaics 2013-2017 & IHS

Let s not declare Mission Accomplished too soon There is lots of work left to make better modules!

Opportunities for better solar utilization More efficient panels that still cost < $0.5/W Replace glass with plastic to reduce cost and weight Make panels flexible and incorporate them into rooves Reduce the cost of permitting and finding customers Improve financing of solar projects Find better ways to use power from an intermittent source (e.g. let utilities decide when to charge electric cars) Improve storage (better batteries or solar fuels) Carbon tax

Perovskite Solar Cells are Soaring Jul 2013 Grätzel 15% Sept 2013 Snaith 15.4% Snaith et al., Nature 2013 Grätzel et al., Nature 2013 6

Perovskite Solar Cells and Polycrystalline Tandems A route to high efficiency and low cost.

Hybrid perovskite solar-cell absorbers Ian Smith, 1 Eric Hoke, 2 Daniel Slotcavage, 2 Emma Dohner, 1 Diego Solis- Ibarra, 1 Andrea Bowring, 2 Michael McGehee, 2 and Hemamala Karunadasa 1 Departments of Chemistry 1 and Materials Science and Engineering 2 Stanford University

The 3D perovskite structure Pb 2+ I CH 3 NH 3 + 3D ABX 3 perovskite e.g. (CH 3 NH 3 )PbI 3

Layered perovskites Pb 2+ C 4 H 9 NH 3 + I 3D ABX 3 perovskite e.g. (CH 3 NH 3 )PbI 3 2D A BX 4 perovskite e.g. (NH 3 C 4 H 9 )[PbI 4 ] Mitzi Prog. Inorg. Chem. 1999, 48, 1

Self-assembly reactions are inexpensive and scalable

3D lead-iodide perovskite absorbers: strengths 1. Inexpensive precursors and solution-state film deposition methods PbI 2 (CH 3 NH 3 )I in solvent Image of PbI 2 on TiO 2 Liang, Mitzi, Prikas, Chem. Mater. 1998, 10, 403 Burschka, Pellet, Moon, Humphry-Baker, Gao, Nazeeruddin, Gratzel, Nature 2013, 499, 316 Image of (CH 3 NH 3 )PbI 3 formed by 2-step conversion

3D lead-iodide perovskite absorbers: strengths 1. Inexpensive precursors and film deposition methods 2. Device efficiencies have jumped from 4% to >15% in just 5 years! Device efficiency % Year Kojima, Teshima, Shirai, Miyasaka J. Am. Chem. Soc., 2009, 131, 6050 Im, Lee, Lee, Park, Park Nanoscale, 2011, 3, 4088 Kim, Lee, Im, Lee, Moehl, Marchioro, Moon, Humphry-Baker, Yum, Moser, Grätzel, Park Sci. Rep., 2012, 2, 591 Lee, Teuscher, Miyasaka, Murakami, Snaith Science, 2012, 338, 643 Burschka, Pellet, Moon, Humphry-Baker, Gao, Nazeeruddin, Grätzel Nature, 2013, 499, 316 Liu, Johnston, Snaith Nature, 2013, 501, 395 Green, Ho-Baillie, Snaith Nat. Photonics, 2014, 8, 506 Jeon, Noh, Kim, Yang, Ryu, Seok Nat. Mater., 2014, 13, 897

3D lead-iodide perovskite absorbers: strengths 1. Inexpensive precursors and film deposition methods 2. Device efficiencies have jumped from 4% to >15% in just 5 years! 3. Charge carriers are exceptionally long lived. Material defects do not appear to reduce device efficiencies Device efficiency % Year Stranks, Eperon, Grancini, Menelaou, Alcocer, Leijtens, Herz, Petrozza, Snaith Science 2013, 342, 341 Xing, Mathews, Sun, Lim, Lam, Grätzel, Mhaisalkar, Sum, Science 2013, 342, 344

3D lead-iodide perovskite absorbers: strengths 1. Inexpensive precursors and film deposition methods 2. Device efficiencies have jumped from 4% to >15% in just 5 years! CB 3. Charge carriers are exceptionally long lived. Material defects do not appear to reduce device efficiencies 4. Absorbers can also function as charge carriers for electrons or for holes VB Lee, Teuscher, Miyasaka, Murakami, Snaith, Science 2012, 338, 643 Etgar, Gao, Xue, Peng, Chandiran, Liu, Nazeeruddin, Gratzel, M. J. Am. Chem. Soc. 2012, 134, 17396

3D lead-iodide perovskite absorbers: strengths 1. Inexpensive precursors and film deposition methods 2. Device efficiencies have jumped from 4% to >15% in just 5 years! 3. Charge carriers are exceptionally long lived. Material defects do not appear to reduce device efficiencies 4. Absorbers can also function as charge carriers for electrons or for holes Lee, Teuscher, Miyasaka, Murakami, Snaith, Science 2012, 338, 643 Etgar, Gao, Xue, Peng, Chandiran, Liu, Nazeeruddin, Gratzel, M. J. Am. Chem. Soc. 2012, 134, 17396

3D lead-iodide perovskite absorbers: strengths 1. Inexpensive precursors and processing methods 2. Device efficiencies have jumped from 4% to >15% in just 5 years! 3. Charge carriers are exceptionally long lived. Material defects do not appear to reduce device efficiencies 4. Absorbers can also function as charge carriers for electrons or for holes 5. Mixed-halide perovskites can attain many intermediate bandgaps Noh, Im, Heo, Mandal, Seok, Nano Lett. 2013, 13, 1764

3D lead-iodide perovskite absorbers: potential problems 1. These materials are water-soluble sources of toxic Pb 2+ ions 0 days 20 days

3D lead-iodide perovskite absorbers: potential problems 1. These materials are water-soluble sources of toxic Pb 2+ ions 2. The perovskite is not stable to moisture. The black solid decomposes in moist air to form yellow PbI 2 3. Solar cells containing mixed-halide lead perovskites (MA)Pb(I 1-x Br x ) 3 have not achieved the high V OC s that are expected from their higher bandgaps, compared to (MA)PbI 3 (R)PbI 3 (R)Pb(I 1 x Br x ) 3 (1 > x > 0.2) (R)PbBr 3 Band gap 1.6 ev ~1.7 2.2 ev 2.3 ev Highest achieved V OC 1.1 ev ~1.1 ev 1.5 ev Edri, Kirmayer, Kulbak, Hodes, Cahen, D. J. Phys. Chem. Lett. 2014, 5, 429

Improving the moisture resistance of perovskites

The family of hybrid perovskites n = 1 Bandgap = 2.57 ev Exciton binding energy = 220 mev

The family of hybrid perovskites n = 1 Bandgap = 2.57 ev Exciton binding energy = 220 mev Phosphor Dohner, Hoke, Karunadasa J. Am. Chem. Soc. 2014, 136, 1718 Dohner, Jaffe, Bradshaw, Karunadasa J. Am. Chem. Soc. 2014, 136, 13154

The family of hybrid perovskites n = 1 infinity Bandgap = 2.57 ev 1.61 ev Exciton binding energy = 220 mev 40 mev Kojima, Teshima, Shirai, Miyasaka, J. Am. Chem. Soc. 2009, 131, 6050 Im, Lee, Lee, Park, Park, Nanoscale 2011, 3, 4088 Lee, Teuscher, Miyasaka, Murakami, Snaith, Science 2012, 338, 643 Etgar, Gao, Xue, Peng, Chandiran, Liu, Nazeeruddin, Gratzel, J. Am. Chem. Soc. 2012, 134, 17396 Solar-cell absorber

To trap an exciton; to split an exciton n = 1 2 3 infinity Bandgap = 2.57 ev 2.32 ev ca. 2.1 ev 1.61 ev Exciton binding energy = 220 mev 170 mev ca. 40 mev 40 mev T. Ishihara, J. Lumin. 1994, 60 61, 269

A 2D perovskite solar-cell absorber with improved moisture resistance Ian Smith Smith, Hoke, Solis-Ibarra, McGehee, Karunadasa Angew. Chem., Int. Ed. 2014, 53, 11232

A layered perovskite solar-cell absorber h + Hole-transport material Light absorber e Electron-transport material Smith, Hoke, Solis-Ibarra, McGehee, Karunadasa Angew. Chem., Int. Ed. 2014, 53, 11232

2D perovskite absorbers Larger bandgap affords higher open-circuit voltage of 1.18 V

2D perovskite absorbers Larger bandgap affords higher open-circuit voltage Layered structure allows for high-quality films to be deposited through spincoating and high-temperature annealing is not required 2D 2D 3D 3D Left: Crystals of 2D perovskites that grow as plates. Right: SEM images of films of (A) (PEA) 2 (CH 3 NH 3 ) 2 [Pb 3 I 10 ], and (MA)[PbI 3 ] formed from (B) PbI 2, (C) from PbCl 2.

2D perovskite absorbers Larger bandgap affords higher open-circuit voltage Layered structure allows for high-quality films to be deposited through spincoating and high-temperature annealing is not required The 2D material is far more moisture resistant and devices can be fabricated under humid atmospheres Higher values of n as single-phase materials or as mixtures may allow for lower bandgaps and higher carrier mobility in the inorganic layers while the organic layers provide additional tunability.

The 2D structure may offer greater tunability for material optimization Substitutions for both the small and large organic cations Substitutions in the organic layer: Hydrophobic molecules Molecules that absorb light Conductive molecules Substitutions in the inorganic layer: Connectivity of the sheets Number of sheets (n = 3, 4, 5) Mixed metal/halide sheets

Light-induced reversible changes in mixed-halide perovskites 1. The absorption spectrum of (MA)(PbI 1-x Br x ) 3 shows a gradual blueshift with increasing bromide content 2. The emission spectrum follows a similar trend 3. But continuous illumination induces dramatic changes... Dr. Eric Hoke Hoke, Slotcavage, Dohner, Bowring, Karunadasa, McGehee manuscript submitted

Mixed-halide perovskites under continuous illumination 1. Photoluminescence (PL) spectra of (MA)Pb(I 1 x Br x ) 3 (x > 0.2) perovskites develop a new red-shifted peak at 1.68 ev that grows in intensity under constant, 1-sun illumination in less than a minute 2. The position of this new peak is independent of halide stoichiometry for 1 > x > 0 3. These transitions are reversible. The original PL can be regained after the material is left in the dark for a few minutes

Characterization of the light-soaked material (x = 0.6) Dark Light 1. A new absorption shoulder forms around 1.7 ev after light soaking, which completely disappears after the devices are left in the dark for 1 h 2. All x-ray diffraction peaks split upon light soaking. The original sharp diffraction patterns are obtained after the films are left in the dark

Proposed mechanism for light-induced reversible trap formation

Proposed mechanism for light-induced reversible trap formation light dark Homogenous mixture Segregated material

Characterization of the light-soaked material (x = 0.6) 1. The absorption shoulder in the light-soaked x = 0.6 perovskite has an absorption coefficient similar to the expected value if ~1% of the material converted into the x = 0.2 perovskite 2. The split x-ray diffraction peaks can be fitted to peaks from perovskites with high (x = 0.2) and low (x = 0.7) iodide content

Proposed mechanism for light-induced reversible trap formation Halide conductivity activation energies in other perovskites CsPbCI 3 CsPbBr 3 KMnCI 3 CuCdCl 3 KPbI 3 CuSnI 3 CuPbI 3 0.29 ev 0.25 ev 0.39 ev 0.36 ev 0.32 ev 0.29 ev 0.26 ev We calculate an activation energy for the initial growth rate of the new PL peak of 0.27(6) ev Mizusaki, Arai, Fueki Solid State Ionics, 1983, 11, 203 Kuku Solid State Ionics, 1987, 25, 1 Kuku Solid State Ionics, 1987, 25, 105 Kuku Thin Solid Films, 1998, 325, 246

Light-induced reversible trap formation in hybrid perovskites 1. The reversible formation of luminescent trap states in (MA)Pb(I 1-x Br x ) 3 is consistent with halide segregation under illumination 2. We see this behavior for mixed halide perovskites with other organic cations, and for films deposited by different methods. We even see this behavior in single crystals 3. Light-induced trap formation limit the attainable voltages from mixed-halide perovskites. We must find methods to prevent this or explore alternative strategies to increasing the voltages of perovskite absorbers (CH 3 NH 3 )PbI 3 E g = 1.6 ev PL ~ (CH 3 NH 3 )Pb(I 0.8 Br 0.2 ) (CH 3 NH 3 )PbBr 3 E g = 2.3 ev

Emma Dohner, Richard Hoft, Abraham Saldivar, Adam Slavney, Ian Smith, and Dr. Diego Solis-Ibarra Colin Bailie, Becky Belise, Andrea Bowring, Greyson Christoforo, William Nguyen, Daniel Slotcavage, and Dr. Eva Unger Prof. Michael McGehee Dr. Eric Hoke

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