NASA / TM--2002-211833 IEC EC-2002-20154

Thin-Film Organic-Based Solar Cells

for Space Power

Sheila G. Bailey

Glem_ Research Center, Cleveland, Ohio

Jerry D. Harris

Cleveland State University, Cleveland, Ohio

Aloysius E Hepp

Glem_ Research Center, Cleveland, Ohio

Emily J. Anglin

Ohio Aerospace Institute, Brook Park, Ohio

Ryne P. Raffaelle

Rochester Institute of Technology, Rochester, New York

Harry R. Clark, Jr.

Townsend Sci.en.ce and Engineering, hlc., Fitchburg, Massachusetts

Susan T.R Gardner

Ph.ysi.cal Sci.en.ces, In.c., Andover, Massachusetts

Sam S. Sun

Norfolk State Universit_5 Norfolk, Virginia

August 2002
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NASA/TM--2002-211833 IECEC-2002-20154

Thin-Film Organic-Based Solar Cells

for Space Power

Sheila G. Bailey

Glelm Research Center, Cleveland, Ohio

Jerry D. Harris

Cleveland State University, Cleveland, Ohio

Aloysius F. blepp

Glelm Research Center, Cleveland, Ohio

Emily J. Anglin

Ohio Aerospace Institute, Brook Park, Ohio

Ryne I-: Raffaelle

Rochester Institute of Technology, Rochester, New York

Harry R. Clark, Jr.

Townsend Science and Engineering, In.c., Fitchburg, Massach.usetts

Susan T.P. Gardner

Physical. Sciences, Inc., A:ndover, Ma ssach.usetts

Sam. S. Sun.

Norfolk State Universit),; Norfolk, Virginia

Prepared :for the

37fl_ In.tersociety Energy Conversion. Engin.eering Conference

sponsored by the Institute of Electrical and Electronics Engineers, Electron Devices Society

Washington., DC, July 28-August 2, 2002

National Aeronautics and

Space Administration

Gleam Research Center

August 2002
Trade names or manufacturers' names are used in this report for

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Available electronically at http: //gltrs.grc.nasa.gov
THIN-FILM ORGANIC-BASED SOLAR CELLS FOR SPACE POWER

Sheila G. Bailey

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

216-433-2228, 216-433-6106, sheila.g .bailey@g rc.nasa.gov

Jerry D. Harris

Cleveland State University

Cleveland, Ohio 44115

Aloysius F. Hepp

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Emily J. Anglin

Ohio Aerospace Institute

Brook Park, Ohio 44142

Ryne P. Raffaelle

Rochester Institute of Technology

Rochester, New York 14623

Harry R. Clark, Jr.

Townsend Science and Engineering, Inc.

Fitchburg, Massachusetts 01420

978-345-9090, 978-345-9292, sundye@ziplink.net

Susan T.P. Gardner

Physical Sciences Inc.

Andover, Massachusetts 01810

978-738-8231,978-889-3232, gardner@psicorp.com

Sam S. Sun

Norfolk State University

Norfolk, Virginia 23504

757-823-2993, 757-823-9054, ssun@nsu.edu

ABSTRACT

Recent advances in dye-sensitized and organic

polymer solar cells have lead NASA to investigate the

potential of these devices for space power generation.

Dye-sensitized solar cells were exposed to simulated

low-earth orbit conditions and their performance

evaluated. All cells were characterized under

simulated air mass zero (AM0) illumination. Com_)lete

cells were exposed to pressures less than 1× 10- torr

for over a month, with no sign of sealant failure or

electrolyte leakage. Cells from Solaronix SA were

rapid thermal cycled under simulated low-earth orbit

conditions. The cells were cycled 100 times from

-80 °C to 80 °C, which is equivalent to 6 days in orbit.

The best cell had a 4.6% loss in efficiency as a

result of the thermal cycling. In a separate project,

novel -Bridge-Donor-Bridge-Acceptor- (-BDBA-) type

conjugated block copolymer systems have been

synthesized and characterized by photoluminescence

(PL). In comparison to pristine donor or acceptor, the

PL emissions of final -B-D-B-A- block copolymer films

were quenched over 99%. Effective and efficient

photo induced electron transfer and charge

separation occurs due to the interfaces of micro

phase separated donor and acceptor blocks. The

system is very promising for a variety high efficiency

light harvesting applications. Under an SBIR contract,

fullerene-doped polymer-based photovoltaic devices

were fabricated and characterized. The best devices

showed overall power efficiencies of -0.14% under

white light. Devices fabricated from 2% solids content

solutions in chlorobenzene gave the best results.

Presently, device lifetimes are too short to be practical

for space applications.

INTRODUCTION

Inexpensive, lightweight inorganic materials such

as amorphous Si, CulnSe2 and CdTe are currently

being explored for space-based energy conversion.

Next generation thin-film technologies may well

involve a revolutionary change in materials to organicbased devices. These materials offer the possibility

of even lower-cost and higher power-to-weight ratios

that may be mission enabling for Space Solar Power,

Solar Electric Propulsion, and off-grid military

applications, as well as numerous civilian and

commercial off-grid uses. NASA Glenn Research

Center currently supports a small in-house and

extramural program exploring these technologies.

However, to be useful for applications in space, any

solar cell which is developed must not only meet

weight and AM0 efficiency goals, but also must be

NASA/TM--2002-211833 1
durable enough to survive launch and thermal and

radiation environments of space.

Nanocrystalline dye-sensitized solar cells (ncDSC) have been under development for over a

decade, and the ruthenium dyes are reported to be

stable to at least 180 °C and under exposure to

ultraviolet radiation (Amirnas et al., 2000; Kohle et al.,

1997). Reported efficiencies for liquid electrolyte cells

fabricated on glass have been in excess of 10%

(AM1.5) (Gratzel, 2000) and recent advances in solid

electrolytes (Bach et al., 1998) have lead us to

evaluate dye-sensitized solar cells for space power

applications. Additionally, under a NASA SBIR

program robust long-lived dye solar cells on

lightweight plastic have been reduced to practice. At

even modest efficiencies this program holds the

realistic promise for topping the 1 kilowatt per

kilogram power to weight ratio in the very near future.

Both the individual components and complete dyesensitized solar cells have had extensive terrestrial

environment testing, and the results of the testing

have been very promising (Hinsch et al., 2001).

However, very little, if any space environment testing

has been done on dye-sensitized cells. Our in-house

work focused on testing dye-sensitized solar cells

under simulated LEO space conditions. Typically,

LEO missions are flown in circular orbits at space

shuttle altitudes and can range up to 2000 km. They

are characterized by low levels of radiation from

trapped electrons and protons, exposure to UV

radiation and 6000 thermal cycles per year as the

spacecraft moves in and out of the earth's shadow

and completes an orbit roughly every 90 minutes.

LEO missions put a premium on beginning-of-life

(BOL) efficiency and thermal cycle survivability, with

typical temperature ranges of 200-350K (Bailey and

Flood, 1998). Typical LEO missions applications are

weather monitoring, earth observation/global climate

monitoring, military observation and

telecommunication systems. Life times for these

missions range from several months to several years.

In addition to the dye-sensitized solar cell projects,

work has also been supported in the area of organic

polymer photovoltaics. The high volume, low cost

fabrication ability of organic cells will allow for square

miles of solar cell production at one-tenth the cost of

conventional inorganic materials. Plastic solar cells

take a minimum of storage space and can be inflated

or unrolled for deployment. In comparison to current

commercial inorganic photovoltaic materials,

polymeric photovoltaic materials have the advantages

of versatile fabrication schemes and low cost on

large-scale production, therefore exhibit potential for

future large-scale solar industry. For space and any

portable applications, the lightweight, flexible shape of

polymers are other key advantages. While the power

conversion efficiency for inorganic photovoltaic cells

have reached nearly 30% (Green et al., 2001), it is

only a fraction of that for recently developed polymer

photovoltaic systems (Yu et al., 1995; Granstrom et

al., 1998; Shaheen et al., 2001). Therefore,

development of highly efficient polymeric photovoltaic

materials, and a better understanding of the

fundamental mechanisms involved in polymer optoelectronic processes has become a critical research

effort. The group at Norfolk State University has been

developing new donor-acceptor polymer systems for

photovoltaic applications, while the group at Physical

Sciences Inc., has prepared working devices using

C60-doped polymers. A summary of the work from the

different groups will be presented.

RESULTS AND DISCUSSION

Dye-sensitized solar cells

For any solar cell to operate in space, it must be

able to tolerate the vacuum of space. This is a

particularly important concern for dye-sensitized solar

cells, because of the liquid electrolytes commonly

used in these devices. Spacecraft in low-earth orbit

will typically experience pressures on the order of 10 -6

torr. To demonstrate that nc-DSC can tolerate these

types of vacuums, several cells were pumped to a

pressure of <1 x 10 -7 torr under dynamic vacuum for

over a month, and the cells exhibited no signs of

leakage or sealant failure.

Two complete cells were also obtained from

Solaronix SA (Aubonne, Switzerland) and upon

receipt were characterized under AM0 illumination

(figure 1, table 1). The cells were then stored in a

desiccator at room temperature for 52 days while

waiting to be rapid thermal cycled and during this time

received only limited exposure to ambient light. Prior

to thermal cycling, the cells were again characterized

under calibrated, simulated AM0 illumination (figure 2,

table 1). It was observed that one of the cells (cell 1)

had a substantial decrease in performance, and the

second cell (cell 2) had only a modest loss of

performance. The large drop in current for cell 1 is

simply attributed to it being a faulty cell. In the

literature, these cells have demonstrated long shelf

lives.

<

g

50

45 ..... Cell 1

Cell 2

35

3O

25

20

15

10

5

0

0.1 0.2 0.3 0.4 0.5 0.6 0.7

Voltage (V)

FIGURE. 1. IV CURVES FOR CELLS 1 AND 2

WHEN CELLS WERE INITIALLY RECEIVED.

NASA/TM--2002-211833 2
TABLE 1. AIR MASS ZERO CHARACTERIZATION

DATA FOR DYE-SENSITIZED CELLS.

Initial AM0 Pre-cycling Post-cycling

Measure Measure Measure

Cell 1, area 3.68 crn2 3.68 crn2 3.68 crn2

Isc 40.3 mA 14.3 mA 10.8 mA

Voc 677 mV 687 mV 663 mV

Imax 32.4 mA 11.1 mA 8.76 mA

Vmax 454 mV 499 mV 472 mV

Pmax 14.7 mW 5.55 mW 4.13 mW

F.F. 53.9 56.3 57.6

Eft. 2.92 % 1.10 % 0.82 %

Cell 2, area 3.71 crn2 3.71 crn2 3.71 crn2

Isc 45.8 mA 41.4 mA 36.5 mA

Voc 670 mV 672 mV 657 mV

Imax 37.7 mA 33.4 mA 30.0 mA

Vmax 426 mV 404 mV 431 mV

Pmax 16.0 mW 13.5 mW 12.9 mW

F.F. 52.3 48.5 54.0

Eft. 3.16 % 2.66 % 2.54 %

45

4O

35

3O

25

2O

15

10

5

0

..... Cell 1

Cell 2

i

i i i i i i

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Voltage (V)

FIGURE. 2. IV CURVES MEASURED FOR CELLS 1

AND 2 FOLLOWING STORAGE AND PRIOR TO

RAPID THERMAL CYCLING.

Following the second AM0 characterization, the

cells were rapid thermal cycled between -80 °C and

80 °C, which roughly corresponds to the temperature

swings the cells would experience in a low-earth orbit.

A spacecraft in low-earth orbit endures approximately

6000 thermal cycles per year. For our initial testing of

the cells, they were rapid thermal cycled 100 times,

which corresponds to six days in orbit. After thermal

cycling, the cells were once again characterized

under AM0 illumination (figure 3, table 1). There was

a measurable decrease in the performance of both

cells, with that of cell 1 being the most dramatic.

Upon examination, cell 1 lost a substantial amount of

electrolyte during thermal cycling. The electrolyte

appears to have escaped under or through the Surlyn

1702 polymer seal, as the seal was stained yellow on

one side of the cell following thermal cycling.

Physically, cell 2 survived the thermal cycling

reasonably well, with no signs of electrolyte loss.

However, it did have a 4.6% drop in efficiency,

caused mainly from a decrease in current produced

by the cell.

40

3 5 _ .... Cell 1

30

25

20

15

10 ............................. -_

0

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Voltage (V)

FIGURE. 3. IV CURVES FOR CELLS 1 AND 2

FOLLOWING RAPID THERMAL CYCLING.

Current dye-sensitized solar cells lack stability at

elevated temperatures (85 °C) (Hinsch et al., 2001).

However, due to our limited amount of data, it is

difficult to determine whether the decrease in

performance of cell 2 was from the elevated cycle

temperatures, or another failure mechanism. A longterm study is in progress, and the results will be

reported when available. As mentioned above, the

lack of stability of cell 1 is likely due to a defective cell.

This is evident from the thermal cycling data and the

loss of electrolyte during cycling. Although Surlyn

1702 has a reported softening temperature of 65 °C, if

the failure of cell 1 had been caused from excessive

heating of the cells, both cells would have been

expected to exhibit the same loss of electrolyte during

rapid thermal cycling.

Donor-acceptor polymers

Donor (p-type) conjugated polymers help stabilize

and transport the positive charges (holes), and

acceptor (n-type) conjugated polymers help stabilize

and transport the negative charge (electrons). Thus

photo induced electron transfer and charge

separation observed in organic composites of donors

and acceptors provided a potential organic molecular

approach to high efficiency light harvesting or optoelectronic applications (Granstrom et al., 1998). Such

systems and devices have already been

demonstrated using polythiophene/CN-PPV bilayers

(Granstrom et al., 1998), MEH-PPV/CN-PPV blends

(Yu and Heeger, 1995), MEH-PPV/C60 bilayers and

NASA/TM--2002-211833 3
blends (Yu et al., 1995), MEH-PPV/PS-C60 di-block

copolymers (Stalmach et al., 2000).

In our current approach, a conjugated donor block

"RO-PPV" or (D) is coupled to a conjugated acceptor

block "SF-PPV" or (A) via a short non-conjugated

bridge unit (B) to form a D-B-A-B type block

copolymer system. In this system, the charge

separation can be maximized since the interfacial

area can be conveniently controlled via the size of

block copolymer segment. Every donor block can be

built in a convenient reach of an acceptor block, within

the exciton diffusion range. On the other hand, the

charge recombination between the donor and

acceptor blocks at the backbone junction is hindered

due to a non-conjugated aliphatic bridge unit.

Figure 4 shows the chemical structures and

synthetic scheme of-DBAB-. The donor block (D) is

an alkyloxy derivatized polyphenylenevinylene or

"RO-PPV", and the acceptor block (A) is an alkylsulfone derivatized polyphenylenevinylene or "SFPPV". Two bridge units were investigated: the first

was a dialdehyde terminated bridge (unit 1), and the

second was a diamine terminated bridge (unit 2).

When bridge unit 1 was used, both donor and

acceptor blocks were synthesized with terminal

phosphate groups. When amine terminated bridge

unit 2 was used, both donor and acceptor blocks were

synthesized with terminal aldehyde groups. Due to

space limitations, we briefly present only the

photoluminescence (PL) properties of-DBAB- in

comparison to D and A blocks.

D _ B- D-B

Excess B -B-I)-B .A.

A _ B- A-B

RO D = Dono¢ Block

Y V

OR

ROzS A = Aceeptor Block

RO _8

V -_,(

OR

R=C 2H5,C8_'117.C 10H21 Y=C H2PO(O C2H$)2,CHO

OH C --_0 --{C H _)p--O "_CH O H2N-(CH ?'q-N H 2

Bridge Unit I = B Bridge Unit 2 = B

FIGURE 4. DONOR AND ACCEPTOR BLOCK

COPOLYMER SYSTEMS INVESTIGATED.

The donor block film has a PL emission maximum

at -570 nm, and the acceptor block film has a PL

emission maximum at -590 nm (figure 5), yet the PL

emission of -DBAB- film was quenched over 99%.

Spikes at 470 nm and 510 nm are from film reflected

excitation beam. In the figure, the -BDBA- curve is

arbitrarily magnified for clarity. In dichloromethane,

-DBAB- PL quenched about 80 % in comparison to D

or A. Additionally, the UV-Vis absorption spectrum of

-DBAB- is almost an exact overlap of D and A. Thus

ground states electron transfer in -DBAB- is not

obvious, and the PL quenching is mainly due to photo

induced electron transfer between donor and acceptor

blocks. Preliminary AFM studies revealed certain

micro phase separated pattern in the -BDBA- films on

silicon substrates. Detailed microscopic studies are

still underway and will be reported elsewhere.

4i_............ _0............ _o........... _ ............ _0_............ _ ........... %........... >;_............ ;_0

Wavelength (ntr)

FIGURE 5. PL EMISSION SPECTRA OF D (ROPPV), A (SF-PPV), AND DBAB FILMS.

Fullerene-containinq Polymeric Devices

Photovoltaic devices have been fabricated by

blending C60 with conducting polymers, but the

solubility of C60 is too low to achieve a high loading

that can form a low resistance electron transport

network. These devices have a power conversion

efficiency of -3% under monochromatic light.

Although this efficiency is much lower than that of

silicon photovoltaic devices, the Voc that can be

obtained is much higher (<IV for silicon, >2V for

polymer) so fewer polymer-based cells need to be put

in series to achieve the same net voltage output.

To increase the efficiency of these polymer

photovoltaic devices, researchers (Yu, 1995; Yu et al.,

1995) developed new conducting polymer composites

that contained an electron-donating species and an

electron accepting species in a bicontinuous network.

These photovoltaic systems are based on the

mechanism of photoinduced charge separation, as

previously mentioned. The most successful of these

systems is based on the polymer poly(pphenylenevinlyene) (PPV). The electron donor phase

utilizes a well-known soluble PPV derivative, poly(2-

methoxy-5-(2'-ethylhexyloxy- 1,4-phenylvinylene),

which is more commonly known as MEH-PPV. The

acceptor phase utilizes one of two soluble forms of

C60 known as [6,6] PCBM and [5,6] PCBM. The

structures of these compounds are shown in Figure 6.

Efficient current collection in these devices is

achieved by using two electrode materials whose

work functions span the energy of the lowest

unoccupied molecular orbital (LUMO) of C60, as

shown in Figure 7. The use of Ca (or AI) as the

cathode and indium tin oxide (ITO) as the anode sets

up an internal field in the device in which hole are

driven to the ITO:MEH-PPV:C60 interface and

NASA/TM--2002-211833 4
00CH_

MEH-PPV PCBM

FIGURE 6. STRUCTURES OF MEH-PPV & PCBM.

4,7V

ITO

CB

VB

' • "_1-- 3.9 V

Lurno of C60

FIGURE 7. FLAT BAND SCHEME OF A

CA/POLYMER + C60/ITO TUNNEL DIODE..

ADAPTED FROM [SARICIFTCI, 2000].

electrons are collected at the Ca:MEH-PPV:C60

interface.

The limiting factors in the performance of these

devices are: 1) the number of available acceptor sites

limited by the solubility of C60 in MEH-PPV, 2) the rate

of electron transfer from the polymer to the electron

acceptor, and 3) the limitation on electron transport in

the C60 component of the bicontinuous network.

Polymers solutions were prepared by dissolving

either MEH-PPV or a MEH-PPV:PCBM mixture (1:4

ratio) in chlorobenzene or chloroform, with the solid

content ranging from 1 to 4%. The polymer solutions

were spin-coated onto ITO-coated glass fitted with

wire electrodes. The resulting films ranged in

thickness from 600 to 800 ,& for MEH-PPV:PCBM

mixtures to -1000 ,& for MEH-PPV. Devices were

fabricated by thermally evaporating a metal contact

on top of the polymer film, encapsulating in glass and

sealing with Master Bond EP65HT-1 epoxy to protect

the device from air during evaluation (figure 8). Two

contact configurations were used. The first was

ITO/polymer/Ca/AI, with the metal layers each 1000 ,&

thick. The second configuration was ITO/

polymer/LiF/AI, with a <9 ,& layer of LiF instead of

1000 ,& of Ca. As evident in figure 8, three devices

are produce on each piece of ITO-coated glass.

To reduce premature degradation, the

devices were kept in the dark until they were

characterized. Devices containing PCBM

showed efficiencies that were much higher than

for devices with MEH-PPV alone, and device

ITO Anode

Sealing

EpoXy

F;4868

FIGURE 8. PHOTOVOLTAIC DEVICE WITH A

CONFIGURATION OF ITO/MEH-PPV/CA/AL AND

AN ACTIVE AREA OF -6 MM 2

prepared using chlorobenzene solutions showed

slightly higher efficiencies than those made with

chloroform. In addition, films deposited from

solution containing 2% solids gave the highest

efficiencies.

However, the efficiencies were much lower than

those reported in the literature for similar devices. Our

best device, fabricated from a 2% solids content

solution in chlorobenzene, showed an efficiency of

0.14%, significantly lower than the 2.5% previously

reported (table 2). The open circuit potentials were

approximately half of the literature values of -1.6 V for

MEH-PPV or MDMO-PPV devices and -0.8 V for the

PCBM-containing devices. In addition, our shortcircuit currents were significantly lower. The source

of our lower efficiencies is unclear, but we suspect

that purity plays a large role. Although device

fabrication was performed under dust and oxygenfree conditions, extreme lengths were not taken to

purify the MEH-PPV or PCBM used in the devices.

Further more, a phenomenon that has been under

reported is the low stability of these devices.

Neugebauer, et al. (2000) tested the stability MDMOPPV:PCBM (1:3 by mass) devices under argon for 12

hours with constant cycling from bias voltages of-2 V

to +2 V under 10 mW/cm of white light and observed

no significant degradation. Under an atmosphere of

pure oxygen, the same devices showed a factor of

three decrease in the short circuit current and no

decrease in the open circuit potential. However, our

devices were much less stable. Figure 9 illustrates

this situation, showing two cycles that were measured

taken one after the other. Clearly, lifetimes for these

devices are currently too short for practical

applications, and this is a key area that must be

address in the future.

NASA/TM--2002-211833 5
TABLE 2.

DEVICES

Ref.

Shaheen,

2001

COMPARISON OF PSI PHOTOVOLTAIC

WITH THOSE PREVIOUSLY REPORTED.

system eft. Isc Voc (V) FF

'mNcm 2

MDMO-PPV:PCBM 2.5% 5.25 0.82 0.61

C6o blend (1:4 weight

ratio), spin coat from

chlorobenzene.

PEDOT/PSS HTL

and LiF/AI electrode

Sebeyehu, MDMO-PPV:PCBM 1.5% 1 0.60 0.30

2001 C6o blend (1:3 weight

ratio), spin coat from

xylene. PEDOT hole

transport layer used.

Fromherz, MDMO-PPV:PCBM 1.5% 0.07 0.72 -0.30

2000 blend, (1:3 weight

ratio)

Yu, Gao, MEH-PPV:PCBM 2.9% 2 -0.82 -0.36

etal, 1995 blend (1:4weight (est.) (est.)

ratio) spin coat from

dichlorobenzene

same as MEH-PPVspin coat 0.02% 0.006 1.60 N/A

above from xylene solution (est.)

Marcos Poly(phenylene 0.10% 0.42 0.83 0.29

Ramos, ethynylene vinylene)

2001 with pendant C6o,

spin coat from CHCI3.

1 C6o every 4 units.

PSI MEH-PPV:PCBM 0.14% 0.027 0.45 0.45

blend (1:4 weight

ratio) spin coat from

a 2% chlorobenzene

sol'n

PSI MEH-PPV:PCBM 0.11% 0.255 0.38 0.29

blend (1:4 weight

ratio) spin coat from

a 2% chlorobenzene

sol'n

PSI MEH-PPV spin coat 4.57x 9.61E-5 0.80 0.15

from a 2% xylene 105%

solution

lxlo -3

lxlO-5

lx10-6

oi_ o12 o'3 oi_ o15 o6 o17 0.8

v

FIGURE 9. TWO SUBSEQUENT SCANS OF A PSI

DEVICES FABRICATED FROM A 2%

CHLOROBENZENE SOLUTION.

REFERENCES

Amirnasr, M., Nazeeruddin, M.K., and Gr&tzel, M.,

2000, "Thermal stability of cis-dithiocyanato(2,2'-

bypyridyl-4,4'-dicarboxylate) ruthenium(ll) photosensitizer in the free form and on nanocrystalline TiO2

films," Thermochimica Acta, 348, 105-114.

Bach, U., Lupo, D., Comte, P., Moser, J.E.,

Weiss6rtel, F., Salbeck, J., Spreitzer, H., and Gr&tzel,

M., 1998 "Solid-state dye-sensitized mesoporous TiO2

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NASA/TM--2002-211833 6
Form Approved REPORT DOCUMENTATION PAGE

OMB No. 0704-0188

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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

August 2002 Technical Memorandum

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Thin-Film Organic-Based Solar Cells for Space Power

& AUTHOR(S)

Sheila G. Bailey, Jerry D. Hm'ris, AJoysius F. tlepp, Emily J. Anglin,

Ryne R Raffaelle, HmTy R. Clark, Jr., Susan T.R Gardner, and Sam S. Sun

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

John H. Glenn Resem'ch Center at Lewis Field

Cleveland, Ohio 44135 - 3191

WU-755-A4-01-00

8. PERFORMING ORGANIZATION

REPORT NUMBER

E---13527

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

National Aeronautics and Space Administration

Washington, DC 20546-0(101 NASA TM------.2002-211833

IECEC.---2002----20154

11. SUPPLEMENTARY NOTES

Prepared for the 37th Intersociety Energy Conversion ]'ngineering Conference sponsored by the Institute of Electrical and Electronics Engineers, Electron

Devices Society Washington DC July 28 August 2 2002. Sheila G. Bailey and Aloysius F. Erepp, NASA Glenn Research Center; Jerry D. Hmrris,

Cleveland State University, Cleveland, Ohio Emily J. Anglin Ohio Aerospace Inslitule Brook Park Ohio Ryne P. Raffaelle, Rochester Institute of

) )

"I?chnology, Rochester, New York; Harry R. Clark, Jr., 'Ibwnsend Science and Engineering, Inc., Fitchburg, Massachusetts Susan T.I. Gardner I hvsical

Sciences, Inc., Andover, Massachusetts; and Sam S. Sua, Norfolk State University, Norfolk, Virginia. Responsible persoa, Sheila G. Bailey, orgamzation

code 5410, 216 433 2228.

12a, DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified - Unlimited

Subject Category: 25 Distribution: Nonstandard

Available electronicaJly at bttp://glt:.-s._rc.nasa.aov

"l-his publication is available from the NASA Center for AeroSpace Information, 301-621-0390.

12b. DISTRNBUTION CODE

13. ABSTRACT (Maximum 200 words)

Recent advances in dye.--se.nsitized and organic polymer solar ceils have lead NASA to investigate, the potential of these devices for space

power generation. Dye-sensitized solar cells were exposed to sinmlated low-earth orbit conditions and their performance evaluated.

All cells were characterized under simulated air mass zero (AM()) illumination. Complete cells were exposed to pressures less than

lxl 0 7 torr for over a month, with no sign of sealant failure or electrolyte leakage. Cells from Solaronix SA were rapid thermal cycled

under simulated low-earth orbit conditions. The cells were cycled 100 times from -80°C to 80°C, which is equivalent to 6 days in orbit.

q[he best cell had a 4.6 percent loss in efficiency as a result of the thermal cycling. In a separate project, novel -Bridge-l)onor-BridgeAcceptor- (-BDBA-) type coNugated block copolymer systems have been synthesized and characterized by photoluminescence (PL).

In comparison to pristine donor or acceptor, the PL emissions of final -B-D-B-A- block copolymer films were quenched over

99 percent. Effective and efficient photo induced electron transl)r and charge separation occurs due to the interlaces of lmcro phase

separated donor and acceptor blocks. The system is very promising for a variety high efficiency light harvesting applications. Under an

SBIR contract, fullerene-doped polymer-based photovoltaic devices were fabricated and characterized. The best devices showed overall

power efficiencies of _0_14 percent under white lighL Devices labricated from 2 percent solids content solutions in chlorobenzene gave

the best results. Presently, device lifetimes are too sholl to be practical for space applications.

14. SUBJECT TERMS

Photovoltaic; Space power

17. SECURITY CLASSIFICATION

OF REPORT

Unclassified

NSN 7540-01-280-5500

15. NUMBER OF PAGES

12

16. PRICE CODE

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Unclassified Uncl assifi ed

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