1.021 , 3.021, 10.333, 22.00 : Introduction to Modeling and Simulation : Spring 2012 Part II – Quantum Mechanical Methods : Lecture 10

Solar PV

Jeffrey C. Grossman

Department of Materials Science and Engineering

Massac husetts Institute of T ec hnology

Par t II T opics

1. It ’ s a Quantum W orld: The Theor y of Quantum Mechanics

2. Quantum Mechanics: Practice Mak es P erf ect

3. Fr om Man y-Body to Single-Par ticle; Quantum Modeling of Molecules

4. Application of Quantum Modeling of Molecules: Solar Thermal Fuels

5. Application of Quantum Modeling of Molecules: Hydr ogen Storage

6. Fr om Atoms to Solids

7. Quantum Modeling of Solids: Basic Pr oper ties

8. Advanced Pr op . of Materials: What else can w e do?

Summar y

• A bit of discussion of PSET 6

• Solar PV - Mor e Motivation

• Solar PV - the vie wpoint of the elect r on!

• Ho w computational quantum mechanics can impact solar PV

Energ y f r om the Sun

Courtesy of SOHO/EIT (ESA & NASA) consortium.

• Energ y r eleased b y an ear thqua k e of magnitude 8 (10 17 J):

• the sun deliv ers this in one second

• Energ y humans use ann uall y (10 20 J):

• sun deliv ers this in one hour

• Ear th ’ s total r esour ces of oil (3 trillion bar r els, 10 22 J):

• the sun deliv ers this in tw o d a ys

Time Magazine , 3 Apr il 2006

© Time Magazine. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/ .

Cost of Inaction?

Image by Dr. Pieter Tans, NOAA/ESRL and Dr. Ralph Keeling, Scripps Institute of Oceanography .

Grinnel Glacier: 1910 photo by Fred Kiser (top); 1997 photo by Dan Fagre (bottom). Courtesy of GNP archives.

W arming is Real and Has Real Eff ects

MODIS images from NASA's Terra satellite courtesy of Ted Scambos, National Snow and Ice Data Center, University of Colorado, Boulder.

Betw een Jan 31, 2002

Ja n 3 1

Fe b 1 7

Fe b 2 3

Mar 5

and Mar ch 5, 2002 a chunk of the Larsen B ice shelf the size of Rhode Island disintegrated.

Images fr om NASA's T er ra satellite , National Sno w and Ice Data Cente r , Univ ersity of Colorad o , Boulde r .

Sur v e ys sho w the mountain pine beetle has inf ested 21 million acr es and killed 411 million cubic f eet of tr ees -- double the ann ual ta k e b y all the loggers in Canada. In se v en y ears or soone r , the F or est Ser vice pr edicts, that kill will nearl y triple and 80 pe r cent of the pines in the central British Columbia f or est will be dead. The W ashington Post, Mar ch 1, 2006

Photo by Leo Rankin/British Columbia Forest Service. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/ .

CO 2 P r ojections

Source: Climate Change 2007: The Physical Science Basis. Contribution of W orking Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change .

Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Figure 10.22 (b). Cambridge University Press.

The seesa w pattern that rides the rising CO2 tr end r esults fr om the ann ual “br eathing” of the ear th.

Natur e “bor r o w[s] CO2 f or plant gr o wth during the summer and r eturn[s] the loan each succeeding winte r . ” – Da vid K eeling

Recent w orld e v ents that slo w ed oil p r oduction

Image by Dr. Pieter Tans, NOAA/ESRL and Dr. Ralph Keeling, Scripps Institute of Oceanography .

Science 310, 1313 (2005)

T emperatur e inf er r ed f r om isotope ratios in the V ostok ice cor e

Carbon dio xide le v els measur ed in the tra pped air bubbles in the same cor e

Photo by Lonnie Thompson, Courtesy of Ohio State University. All rights reserved.

fr om Thin Ice b y Mark Bo w en

© source unknown. All rights reserved.

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“I can get eight p r of essors f r om MIT on both sides of this issue and no one in this r oom will walk a w a y understanding what the y said about climate change . ”

□ Charlie Ba k e r , F ormer Candidate f or Massachusetts Go v ernor

© unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/ .

If warming exceeds 2°C , negativ e eff ects incr ease and catast r ophic changes become mor e li k el y

Courtesy of Hal Harvey. Used with permission.

Cour tesy: Hal Har v e y (Climate W orks)

Abundance of Solar Energ y

A v erage solar po w er incident on Ear th ~ 130,000 TW

Global energ y consumption (2001) ~ 13.5 TW Source: DOE

24%

23%

ENERGY SOURCES

6.7% P etr oleum

Natural Gas

6.5%

Coal Hydr oelectricity

39%

0.75% Nuclear

Solar/Wind/ W ood/ W aste

Nuclear po w er equivalent is 3,300 x 1 GW n uclear po w er plants. (1 f or e v er y 10 miles of coastline or major waterw a y)

Solar Across Scales

Moscone Center: 675,000 W

Residential home: 2400 W

Kenyan PV market: A verage system: 18W

Moscone Center © SunPower/PowerLight Corp. Image of residential roof and Kenyan woman with panel © unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/ .

Solar Land A r ea Requi r ements

150 Km 2 solar panels in Ne vada w ould po w er the U .S. (15% efficient)

J.A. T urne r , Science 285

1999, p . 687.

Image by the United States Geological Survey is in the public domain.

Solar Land A r ea Requi r ements f or ~20TW

Image by Matthias Loster on Wikimedia Commons. License: CC-BY.

Solar PV: Grid Parity

Source: Mckinsey

Lorenz, P., D. Pinner, and T. Seitz. "The Economics of Solar Power." Energy, Resources, Materials: McKinsey & Company, June 2008. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/ .

Aim: capture 10% of electrical generation with PV

Side note: replacing fossil fuels in the de v e loping w or ld wi l l b eco me mu ch more important in the near future.

At 14¢ per kW e h , P V co uld co st-ef f ectiv ely r eplace 10% of electrical energy used in U.S.

No storage needed.

Co uld be deplo yed by 2022, with 0.04% land use.

SOLAR INTENSIT Y :

HO W MUCH AREA IS REQUIRED T O GENER A TE PO WER?

air mass 1 atmosphere

sun Satellite

air mass 1.5

earth

sun

Sola r spectru m outsid e atmosphere: air mass 0 (AM0) 1353 W/m 2

A t earth’ s surface:

sun at z e nith:

air mass 1 (AM1) 925 W/m 2

sun at 45°:

air mass 1.5 (AM1.5) 844 W/m 2

AM1.5 is terrestrial solar cell standard

Comparison of PV Technologies

This image is in the public domain. Source: Wikimedia Commons .

Solar PV technolog y landsca pe (2015)

• Cost/efficiency tradeoff:

• high efficiency modules module efficiency:

h a v e lo w er installation costs

• lo w efficiency modules

h a v e lo w er module costs

7% 9.1%

12.2% 13.2%

15.4%

Image by MIT OpenCourseWare.

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Ho w do w e suppl y 81 kWh/d a y/ person of solar electricity?

Image by MIT OpenCourseWare.

2006: Solar Cell Production Rate: 14 acres / day

2035: Requir ed Solar Cell Pr oduction Rate: 14,000 acr es / da y

PN Ju n cti o n ( b ri ef revi ew)

Equilibrium in a p-n junction is still “dynamic” and there are four kinds of currents contributing to the net zero flow of charge.

(1) Majority Hole Current. Dif fusional current from hole movement from p to n (current from p to n). (2) Minority Hole Current. Drift current from holes moving from n to p, assisted by the electric field

(current from n to p).

(3) Majority Electron Current. Electron dif fusion from n to p from the high concentration gradient (current from p to n).

(4) Minority Electron Current. Electron drift from p to n, assisted by the electric field (current from n to p). In reverse bias (V < 0), the current comes from minority carriers and is due to drift. In forward bias (V > 0), the current arises from majority carriers and is due to dif fusion.

PN Ju n cti o n ( b ri ef revi ew)

The presence of light induces a net positive change in the generation–recombination rate. Roughly speaking, for each type of current, the ef fect of light is:

(1) Majority Hole Current. Relatively unaf fected, if generation occurs evenly on both sides.

(2) Minority Hole Current. Increased, due to the additional carriers now present. The additional carriers resulting from illumination are immediately transferred across the junction in the form of a drift current.

(3) Majority Electron Current. Relatively unaf fected.

(4) Minority Electron Current. Increased, due to the additional carriers now present.

Ef fectivel y , under illumination, the IV characteristic of the PN junction is shifted downwards, by an amount that is directly determined from the photocurrent incident upon the junction.

Photo-excitation Relaxation

CBM

E f Extraction

T ransport

Extraction

E f

T ransport

Recombination

VBM

Fundamental P r ocesses In v ol v ed in Solar Photo v oltaics: Elect r on ’ s Vie w

External Load

The Role of Computational Quantum Mechanics

• What do w e kno w ho w to compute?

• Ho w does it help f or solar PV?

Images of solar panel and strips © sources unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/ .

?

Cr ystalline Silicon Solar PV (80% of cur r ent mar k et)

• Light Absorption

• Band Ga p

• Band Structur e

• Elect r on/Hole T ranspor t

© Helmut Föll. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse .

• Elect r on/Hole Mobilities

σ = e 2 τ ∫

d k

4 π 3

— ∂ f v ( k ) v ( k )

∂ E

Amorphous Silicon Solar PV (3% of cur r ent mar k et)

• Light Absorption (is actuall y pr etty g ood)

• Elect r on-Hole Separation (also not a p r oblem)

• Elect r on/Hole T ranspor t (Holes ar e Slo w!)

• Hole Mobilities

• Hole T ra ps: f r om total energ y diff er ences (E neutral -E charged )

Organic Solar PV

• Light Absorption (need to ca ptur e mor e of the solar spectrum)

• Band ga p

• Elect r on-Hole Separation

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• Orbital energies

P ol y(3-hexylthiophene) (P3HT): E g,exp = 2.1 eV Lo w-energ y photons ar e not absorbed!

R

R

Ega p = Eo Ega p = 0.55Eo Ega p = 1.1Eo

D y e Sensitized Solar PV

Gratzel and O’Regan (Natur e , 1991)

Made up of 3 activ e materials:

• Dy e absorbs light.

• TiO 2 nanopar ticles with v er y

large surface ar ea ta k e electr on.

• Liquid electr ol yte deliv ers ne w electr on fr om cathode to dy e .

ww w .energ y e r .com

Image in the public domain. Via M. R. Jones on Wikimedia Commons .

D y e Sensitized Solar PV

• Biggest p r oblem is a

liquid elect r ol yte .

• Relativ e energ y le v els

of TiO2 and dy e also k e y .

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Summar y

• Energ y is a Major Global Challenge

• The Sun has a Lot of it F or Fr ee but it ’ s T oo Expensiv e to Utilize

• Computational Quantum Mechanics can Help us Understand and Pr edict

PV Ne w Materials

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3.021 J / 1.021J / 10.333J / 18.361J / 22.00J Introduction to Modelling and Simulation

Spring 2012

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