A.F. Hepp, S.G. Bailey, and J.S. McNatt 

Glenn Research Center, Cleveland, Ohio

M.V.S. Chandrashekhar

University of South Carolina, Columbia, South Carolina

J.D. Harris, A.W. Rusch, K.A. Nogales, K.V. Goettsche, and W. Hanson 

Northwest Nazarene University, Nampa, Indiana

D. Amos, V.K. Vendra, and C. Woodbury

University of Louisville, Louisville, Kentucky

P. Hari and K.P. Roberts

Nanotechnology Institute, University of Tulsa, Tulsa, Oklahoma

A.D. Jones, Jr.

Florida Agricultural and Mechanical University, Tallahassee, Florida

Novel Materials, Processing, and Device 

Technologies for Space Exploration With 

Potential Dual-Use Applications

NASA/TM—2015-218866

December 2015

AIAA–2014–3464
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A.F. Hepp, S.G. Bailey, and J.S. McNatt 

Glenn Research Center, Cleveland, Ohio

M.V.S. Chandrashekhar

University of South Carolina, Columbia, South Carolina

J.D. Harris, A.W. Rusch, K.A. Nogales, K.V. Goettsche, and W. Hanson 

Northwest Nazarene University, Nampa, Indiana

D. Amos, V.K. Vendra, and C. Woodbury

University of Louisville, Louisville, Kentucky

P. Hari and K.P. Roberts

Nanotechnology Institute, University of Tulsa, Tulsa, Oklahoma

A.D. Jones, Jr.

Florida Agricultural and Mechanical University, Tallahassee, Florida

Novel Materials, Processing, and Device 

Technologies for Space Exploration With 

Potential Dual-Use Applications

NASA/TM—2015-218866

December 2015

AIAA–2014–3464

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for

Propulsion and Energy Forum 2014

sponsored by the American Institute of Aeronautics and Astronautics

Cleveland, Ohio, July 28–30, 2014
Acknowledgments

NASA Glenn Research Center (GRC) is acknowledged for financial support of the work described in this paper, we thank 

Dr. Dennis Flood for his and support. We acknowledge the contributions of our colleagues: Dr. Geoff Landis, GRC; Drs. Castro, 

Banger, and Jin of Ohio Aerospace Institute; Phil Jenkins and Dave Scheiman, Naval Research Laboratory; Dr. Jon Cowen, Case 

Western Reserve University; Prof. Andy Barron, Rice University; and Prof. Ryne Raffaelle at Rochester Institute of Technology. 

Several of us (Profs. Amos, Hari, and Harris) thank the NASA Experimental Program to Stimulate Competitive Research (EPSCoR) 

program for funding. Prof. M.V.S. Chandrashekhar acknowledges the National Science Foundation (NSF), Office of Naval 

Research, and Department of Energy for financial support. Prof. J.D. Harris gratefully acknowledges financial support from the 

NSF through grant DMR 0840265 and A. Punnoose and J. Brotherton, P. Walker and W.B. Knowlton at Boise State University 

for their assistance. Prof. Andrew Jones acknowledges the Nuclear Regulatory Commission for financial support. 

Available from

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This report contains preliminary findings, 

subject to revision as analysis proceeds.

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NASA/TM—2015-218866 1 

Novel Materials, Processing, and Device Technologies for 

Space Exploration With Potential Dual-Use Applications

A.F. Hepp, S.G. Bailey, and J.S. McNatt 

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

M.V.S. Chandrashekhar

University of South Carolina

Columbia, South Carolina 29208

J.D. Harris, A.W. Rusch, K.A. Nogales, K.V. Goettsche, and W. Hanson

Northwest Nazarene University

Nampa, Indiana 83686

D. Amos, V.K. Vendra, and C. Woodbury

University of Louisville

Louisville, Kentucky 40292

P. Hari and K.P. Roberts

Nanotechnology Institute

University of Tulsa

Tulsa, Oklahoma 74104

A.D. Jones, Jr.

Florida Agricultural and Mechanical University

Tallahassee, Florida 32301

Abstract

We highlight results of a broad spectrum of efforts on lowertemperature processing of nanomaterials, novel approaches to 

energy conversion, and environmentally rugged devices. Solution-processed quantum dots of copper indium chalcogenide 

semiconductors and multiwalled carbon nanotubes from lowertemperature spray pyrolysis are enabled by novel (precursor) 

chemistry. Metal-doped zinc oxide (ZnO) nanostructured components of photovoltaic cells have been grown in solution at 

low temperature on a conductive indium tin oxide substrate. Arrays of ZnO nanorods can be templated and decorated with various semiconductor and metallic nanoparticles. Utilizing ZnO 

in a more broadly defined energy conversion sense as photocatalysts, unwanted organic waste materials can potentially be 

repurposed. Current efforts on charge carrier dynamics in nanoscale electrode architectures used in photoelectrochemical 

cells for generating solar electricity and fuels are described. The 

objective is to develop oxide nanowire-based electrode architectures that exhibit improved charge separation, charge collection and allow for efficient light absorption. Investigation of the 

charge carrier transport and recombination properties of the 

electrodes will aid in the understanding of how nanowire architectures improve performance of electrodes for dye-sensitized 

solar cells. Nanomaterials can be incorporated in a number of 

advanced higher-performance (i.e., mass specific power) photovoltaic arrays. Advanced technologies for the deposition of 

4H-silicon carbide are described. The use of novel precursors, 

advanced processing, and process studies, including modeling 

are discussed from the perspective of enhancing the performance of this promising material for enabling technologies 

such as solar electric propulsion. 

Nomenclature

AAO anodized aluminum oxide

AM0 air mass zero (space solar spectrum)

CBD chemical bath deposition

CNT carbon nanotube

CuInS(e)2 copper indium disulf(selen)ide

DFT density functional theory

DGM dusty gas model; mathematical model of gas

transport in porous media

DSSC dye-sensitized solar cell

Eg bandgap energy

FTO fluorin-doped tin oxide

HR-TEM high resolution-transmission electron microscopy

HW-CVD hot wall-chemical vapor deposition
NASA/TM—2015-218866 2 

IMPS integrated microelectronic power supply

LEO low Earth orbit

MWNT multiwall (carbon) nanotube

SEM scanning electron microscopy

SEP solar electric propulsion

SiC silicon carbide; wide-bandgap semiconductor 

(cubic (3C) and hexagonal (4H) polymorphs) 

TEMPO (2,2,6,6-tetramethylpiperidin-1-yl)oxy

TiO2 titanium dioxide; typically found in either anatase 

or rutile phases

TOPO trioctylphosphine oxide

XRD x-ray diffraction

ZnO zinc oxide; a wide-bandgap semiconductor

1.0 Introduction and Background

Ready and reliable power is an essential cornerstone of any 

successful space exploration venture—both manned and robotic. 

Solar array designs have undergone a steady evolution since the 

Vanguard 1 satellite. Early satellites used silicon solar cells on 

honeycomb panels that were body mounted to the spacecraft; 

early space solar arrays only produced a few hundred watts of 

power. Satellites today require low-mass solar arrays that produce several kilowatts of power. Several new solar array structures have been developed over the past 40 years to improve the 

array specific power and reduce the stowed volume during 

launch. The solar arrays presently in use can be classified into six 

categories: (1) body-mounted arrays; (2) rigid panel planar arrays; (3) flexible panel array; (4) flexible roll-out arrays; (5) concentrator arrays; and (6) high temperature/intensity arrays.

In addition, several proposed space missions have put other 

constraints on solar arrays. Several proposed Earth orbiting 

missions designed to study the Sun require “electrostatically 

clean” arrays. Inner planetary missions and mission to study the 

Sun within a few solar radii require solar arrays capable of withstanding temperatures above 450 °C and functioning at high solar intensities. Outer planetary missions require solar arrays that 

can function at low solar intensities and low temperatures. In 

addition to the near-Sun missions, missions to Jupiter and its 

moons also require solar arrays that can withstand high radiation levels (Ref. 1). 

On Earth, the need for alternative energy is a high priority 

given the constant increase in worldwide population and despite 

recent advances in exploiting such resources, the fact that fossil 

fuel reserves are finite. For important applications involving 

terrestrial uses, price per watt will clearly be a critical driver. 

Conversely, the challenges of aerospace and defense have 

spurred the development of advanced technologies. Over the 

past half-century, researchers at the NASA Glenn Research 

Center (GRC) and their academic and industrial partners have 

researched and developed a number of novel processing technologies, materials, devices, and energy conversion solutions 

for the challenges posed by surviving and even thriving in nearEarth space and non-terrestrial surface operations (Ref. 2). 

We highlight several examples of advanced materials, processing and devices in this overview with examples of power 

technologies for space exploration and end with a discussion of 

their long-term potential for terrestrial applications. It is important to keep in mind the fact that solar cell materials and devices, regardless of the specific class of material(s) or device 

structure, are made to generate electricity or facilitate energy 

conversion processes. An important take-home lesson is that a 

wide array of power generation technologies exists, each technology with its unique ability to meet the difficulties posed by 

challenging mission power requirements (Ref. 3). 

2.0 Inorganic Nanomaterials for Energy 

Conversion and Environmental 

Applications

The inclusion of nanocrystalline materials in photovoltaic devices has been proposed as a means to improve the efficiency 

of photon conversion (quantum dot solar cell) (Ref. 4), enable 

low-cost deposition of thin-films (Ref. 5), provide sites for exciton dissociation (Ref. 6), and pathways for electron transport

(Ref. 7). With respect to their use in quantum dot solar cells and 

exciton dissociation, the size of the nanoparticle is an important 

factor in determining the optoelectronic properties of the material. When the size of a semiconductor quantum dot drops below that of the exciton Bohr radius (of the bulk material) the 

energy levels become quantized and the bandgap increases as 

the particle size decreases. In this size regime the bandgap can 

be “tuned” to a desired energy by adjusting the particle size. 

Quantum dots are also expected to be resistant to degradation 

from electron, proton, and alpha particle radiation, a requirement for use in space solar cells (Refs. 8 to 10). However, new 

generation solar cells based on nanostructured materials promise to enhance light harvesting efficiencies, greatly increasing 

their utility for future energy needs.

2.1 CuInE2 (E = S, Se) and Related 

Nanomaterials From Single-Source 

Precursors

The chalcopyrite semiconductors copper indium disulfide 

(CuInS2) or diselenide (CuInSe2) have seen steady improvements in efficiency for thin-film photovoltaics. The bandgap of 

CuInS2 (Eg = 1.5 eV) is a good match to the AM0 solar spectrum, and CuInSe2 (Eg = 1.1 eV) is a promising low-cost 

electro-optical material (Ref. 11). Thin-film Cu(In,Ga)S2 cells 
NASA/TM—2015-218866 3 

with efficiencies of 12.8 percent have been successfully produced (Ref. 12), while Cu(In,Ga)Se2 cells have been recorded 

with over 20 percent efficiency (Ref. 13). Earlier work in producing quantum dots of I-III-VI2 materials relied on reactions 

involving CuInS2 or CuInSe2 nanoparticles from the chlorides 

and trioctylphosphine oxide (TOPO) (Ref. 14), treatment of a 

CuI

-P(OPh)3/InIII-P(OPh)3 mixture in acetonitrile with (TMS)2S 

(Ref. 15), or treatment of an aqueous mixture of CuCl and 

In2(SO4)3 with hydrogen sulfide or hydrogen selenide, respectively (Ref. 16). 

Controlled synthesis of a desired size nanoparticle is not always simple, especially for the higher-order ternary and tertiary 

materials. If separate sources are used for the different metals 

and chalcogenides, binary materials are often preferentially 

formed as a result of the different solubility of the products and 

reactivity of the precursors. A promising method to circumvent 

the formation of undesirable reaction products researched at 

GRC involved the use of single-source precursors. Singlesource precursors are small molecules that include all the elements required in the final material. These precursors can be 

designed with many properties in mind including stoichiometry, solubility, and volatility. 

A simple molecular precursor (PPh3)2CuIn(SEt)4 (1) 

(Figure 12) was first described by Prof. M. Kanatzidis’s group

(Ref. 17). This neutral complex comprises a copper(I) ion 

bound by two triphenylphosphine ligands, an indium(III) ion 

with two terminal ethanethiolate ligands, and two bridging 

ethanethiolate ligands between the metal centers. This molecule 

was found to decompose to produce CuInS2 powders as depicted in Figure 1. Further work with this class of molecules has 

yielded analogous precursors with desirable properties such as 

lower melting points (including the liquid precursor 

(Pn

Bu3)2CuIn(SEt)4) and higher solubility in organic solvents

(Refs. 18 to 20). Note that this molecular structure is quite “tunable” and affords the ability to substitute for any of the ternary 

(Group 11, Group 13, or Group 16) elements in the I-III-VI2

formula, as shown in Figure 2. 

Figure 1.—Diagram of pyrolysis of [{Ph3P}2Cu(SEt)2In(SEt)2] 

precursor (1) to produce semiconducting CuInS2. 

We briefly describe work with the precursors for the synthesis of CuInS2 or CuInSe2 nanoparticles (Refs. 21 and 22). The 

reactions are outlined in Figure 3. The stepwise method of synthesis, isolating the red intermediates, is required for the purest 

products. If the precursor is brought directly to 250 or 300 °C, 

the final black powder is predominantly CuInS2, but impurity 

peaks are evident in the XRD pattern. X-ray powder diffraction 

patterns (Figure 4) clearly show that pure CuInS2 is the product 

of the reaction at 250 and 300 °C, and CuInSe2 at 275 and 

300 °C. The powder diffraction patterns of the red powders 

from the 200 °C reactions exhibit unusual splitting of the (112) 

peaks into two peaks centered about the expected (112) position; the remaining two peaks (204/220) and (116/312) are in 

their expected positions. In all powder patterns, significant 

broadening of the diffraction lines is apparent; particle sizes of

Figure 2.—Tunable sites for [{R3E}2M(QR’)2M’(QR’)2] architecture using [{Ph3P}2Cu(SEt)2In(SEt)2] as an example.

Synthesis of nanocrystalline CuInS2 and CuInSe2 

from single-source precursors

°

= =− = ′ ′ → ′ ′ = =− =

65 2 3

32 4

65 65

Dioctyl phthalate

200 C

(R C H ; R CH CH ; E S) (PR ) CuIn(ER ) (R C H ; R C H ; E Se)2

2 

2 and 2′ are red-brown powders. Each is washed with toluene and methanol 

to remove unreacted precursor, dried under vacuum, and stored in a glove 

box for future use.

° °

° °

→ ′ ′ →

→ ′ ′ →

2 32 3

2 42 4

Dioctyl phthalate Dioctyl phthalate

250 C 275 C

Dioctyl phthalate Dioctyl phthalate

300 C 250 C

Figure 3.—Reaction scheme for the conversion of the singlesource precursors to CuInS2 or CuInSe2. 
NASA/TM—2015-218866 4 

Figure 4.—Powder XRD patterns for a) 2, 3, and 4, the reaction products of [{PPh3}2Cu(SEt)2In(SEt)2] at 200, 250, and 

300 °C, and b) 2′, 3′, and 4′, the reaction products of 

[{PPh3}2Cu(SeEt)2In(SeEt)2] at 200, 275, and 300 °C.

2.1, 2.8 and 7.4 nm are calculated by the Scherrer formula for 

the 200, 250, and 300 °C CuInS2 powders, and 1.8, 4.4, and 

9.8 nm for the 200, 275, and 300 °C CuInSe2 powders, respectively. The precise identity of the red-brown materials (2 for S 

and 2′ for Se) has not been determined.

The powders were examined by transmission electron microscopy (TEM); typical TEM images are shown in Figure 5. 

Large particles seen (left image) are in fact aggregates of nanoparticles. From the high-resolution TEM (HRTEM) images, it 

appears that the size distribution of the samples is quite large, 

therefore, the sizes calculated by the Scherrer formula from the 

x-ray diffraction data are to be taken as only approximate. In 

conclusion, decomposition of single-source precursors at moderate temperatures affords nanoparticles of CuInS2 and CuInSe2

in good yield. These materials have nanometer-sized dimensions and may find utility in hybrid thin film or quantum dot 

solar cells. Future work includes altering the surface of the nanoparticles to enable dispersion in solvents, narrowing of the 

size distributions, and controlling the quantum dot bandgap as 

a function of size. A further observation to make

Figure 5.—Medium (top) and high-resolution (bottom) TEM images of sample 4′ (CuInSe2). 

is that this same approach utilizing single-source precursors 

and/or low-temperature processing can be used to produce 

quantum dots of the recently discovered perovskite solar cell 

materials that have shown much promise over the past several 

years (Ref. 23).

2.1.1 Low Temperature Growth of ZnO Nanorods 

Doped with Metals and Quantum Dots

In recent years, the wide-bandgap, semiconducting material 

zinc oxide (ZnO) has received significant attention; it has attractive electronic properties, it is relatively inexpensive, it is 

easy to prepare, and it is an environmentally friendly alternative 

to other semiconductors. As a result, it is used for a wide array 

of applications such as photovoltaics (Ref. 24), photoacoustic 

wave devices (Ref. 25), UV transceivers (Ref. 26), and photocatalysis (Ref. 27). 

A method for manufacturing metal-doped ZnO nanostructured 

components of photovoltaic cells grown in solution at low 

temperature on a conductive indium tin oxide substrate (ITO) 

developed at the University of Tulsa (TU) is described. The 

growth of nanorods was achieved using a low-temperature, 

chemical bath deposition (CBD) procedure. Optimal growth 
NASA/TM—2015-218866 5 

parameters were varied and tested with the goal of obtaining the 

greatest nanorod density, uniformity, and light absorption 

properties. Growth temperature, growth time, precursor concentration, cobalt dopant amount, and growth pH were each varied. 

Typically, ZnO based nanostructures and thin films absorb light 

in the UV region. By doping ZnO nanorods with cobalt and other 

metals, we can shift the absorption spectrum of ZnO from UV to 

the visible region. Arrays of ZnO nanorods can be templated using anodized aluminum oxide (AAO) membranes and then decorated with various semiconductor and metallic nanoparticles for 

comparison to doped and undoped ZnO thin films.

The CBD method (Ref. 28) developed at TU to incorporate 

metallic ions into ZnO structure holds great promise as a simple 

scalable, low temperature and cost effective method compared 

to pulsed laser deposition and chemical vapor deposition 

methods for fabricating ZnO nanorods and nanowires. In this 

method 1:1 ratio of 98 percent zinc nitrate hexahydrate 

(Zn(NO3)2•6H2O) and hexamethylenetetramine were added to 

125 mL of High Purity water, then placed in the oven at 95 °C 

for 24 h. Cobalt (II) nitrate hexahydrate, 98+ percent was incorporated into the solution before the hydrothermal process to 

dope at 5 percent. Finally, prepurchased cadmium selenide 

(CdSe) quantum dots in solution were dropped onto grown nanorods. In an attempt to increase efficiency, AAO membranes 

were sputter coated with 25 nm of Ag then adhered to ITO glass 

substrate using silver paste. The same growth procedure was 

followed as the non-spaced nanorods. SEM images were taken 

to verify growth of nanorods through the membrane pores. 

Once verified the membranes were dissolved in dilute NaOH 

leaving behind spaced and ordered nanorods. They could later 

be decorated with quantum dots (Ref. 29). 

The synthesized ZnO nanorods grown via low temperature 

hydrothermal method are demonstrated in Figure 6. Experiments that contained Co doped nanorods were submitted to 

XRD and photoluminescence to assure absorption. ZnO nanorods with CdSe quantum dots are shown in Figure 6. The SEM 

image demonstrates a large amount of quantum dots that had 

adsorbed onto the surface. Photoluminescence was performed 

to demonstrate the shifting wavelength. The AAO membranes 

did space out the nanorods; however, the density of their growth 

is still lacking. Studies involving the impact of concentration 

and temperature adjustments are underway in order to demonstrate rational growth (Ref. 30). 

2.2 Photocatalysis with Zinc Oxide

Nanopowders 

Particle size and shape influences the chemical, physical and 

electronic properties of the zinc oxide and its usefulness in 

the above-mentioned applications. As a result, many have investigated ways of controlling or modifying the size and

Figure 6.—(Top) SEM image of ZnO nanorods 

grown on ITO; (Bottom) SEM image of ZnO nanorods grown on ITO covered in CdSe Quantum 

dots.

morphology of ZnO particles by using different synthetic techniques, and modifying synthesis conditions (Refs. 31 to 34).

The research group at Northwest Nazarene University (NNU) 

has been studying the bulk synthesis of zinc oxide nanoparticles 

and working to control both size and morphology of the nanoparticles prepared by sol-gel synthesis using [Zn(acetate)2] in 

the presence of a variety of amines according to Equation (1) 

(Ref. 35).

[Zn(acetate)2](aq) + amine(aq) + NaOH(aq) → ZnO(s) (1)

The ZnO powders formed from the sol-gel process are then 

air dried and annealed in a nitrogen atmosphere at temperatures 

ranging from 150 to 300 °C for 2 h. X-ray powder diffraction 

confirmed formation of phase pure, wurtzite ZnO. X-ray pow-
NASA/TM—2015-218866 6 

der diffraction data for five samples prepared using five different amines are provided in Figure 7. All of the samples are 

phase pure and highly crystalline.

Although all of the samples are wurtzite ZnO, the presence 

of the different amines profoundly affects both the size and 

morphology of the resulting ZnO powders. Morphologies 

produced include: spheres, rods, needles, plates, and small riceshaped nanoparticles. Scanning electron microscope images of 

six of the powders are provided in Figure 8. Synthesis conditions also impact the size and shape of particles. In general, we 

have found that higher synthesis temperatures yield larger particles, and faster rates of NaOH addition yield smaller particles.

Figure 7.—Powder X-ray diffraction data for ZnO powders obtained by sol-gel 

synthesis at 75  ̊C using different amines. All products were annealed at 

200  ̊C for 2 h in a nitrogen atmosphere.

Figure 8.—SEM images of ZnO powders grown using different amines at different temperatures: 

(A) tris(hydroxymethyl)aminomethane) (tris) at 95 °C, (B) ethylenediamine at 95 °C, (C) hydrazine at 95 ̊C, 

(D) t-butylamine at 95 °C, (E) triethanolamine at 65 °C, (F) 1,6-hexanediamine at 65 °C.
NASA/TM—2015-218866 7 

Figure 9.—Normalized absorbance at 558 nm verses time of ultraviolet irradiation 

(254 nm) of aqueous phenol red solutions in the presence of ZnO powders. The 

amine in the legend corresponds to the amine used in the synthesis of the ZnO.

The NNU research group has also been exploring the photochemical properties of the ZnO powders prepared using the different amines. We have found that the different size and 

morphologies of the powders influences the material’s ability 

to catalyze photochemical reactions. For example, we have 

recently studied the different ZnO powders ability to photocatalyze the decomposition of the dye phenyl red under ultraviolet 

radiation. A summary of photocatalysis data for several of the 

powders is provided in Figure 9. 

The plot is the normalized absorbance verses time for irradiation of phenol red solutions in the presence of ZnO powders prepared using four different amines. In general, it was found that 

smaller particles yielded faster decomposition rates than larger 

particles. Additionally, morphologies with a high surface area-tovolume ratio, such as rods or small, rice shaped crystals, also appear to increase the photocatalytic effectiveness. Therefore, by 

introducing different amines in the same synthetic protocol, we 

are able to modify both size and morphology of the prepared ZnO 

nanoparticles, and in turn impact ZnO’s chemical reactivity.

3.0 Novel Production of Dye-Sensitized 

Solar Cells and Carbon Nanotubes

By the year 2050, the world’s energy utilization will have doubled while fossil fuels utilization may continue to challenge our 

ability to exploit new sources. Fortunately, if just 0.2 percent of 

the Earth’s surface were covered in 10 percent efficient solar cells 

by 2050, our energy needs would be met. The only significant

barrier to such widespread deployment is cost. There are several 

third generation photovoltaics technologies that could make

widespread solar cell deployment economically feasible. 

Important technologies to enable advanced lightweight solar cells 

include dye-sensitized solar cells (DSSCs) (Ref. 7) and new carbon nanomaterials, such as carbon nanotubes (CNTs) (Ref. 36). 

These have both generated intense interest amongst scientists and 

engineers for fundamental insights into energy conversion and 

practical applications(Ref. 37). We outline several efforts geared 

towards advancing these technologies and enabling their inclusion in new, lightweight low-cost solar cells or other power devices for future dual-use applications.

3.1 Efficient Inkjet Printed Dye Sensitized 

Solar Cells

With current DSSC efficiencies peaking at 13 percent

(Ref. 38), the focus of research needs to shift to mass production. As DSSC are a relatively new technology that is constantly 

changing, any factories necessarily need to be flexible to remain 

competitive. Inkjet printing has the flexibility to accommodate 

materials changes and allows for the facile deposition of intricate patterns (Figure 10) without the expensive retooling and 

downtime associated with making new screens for screen-printing. To date, the group at University of Louisville (UofL) has 

printed DSSCs with efficiencies as high as 4.23 percent and can 

consistently produce 4 percent efficient DSSCs. While UofL’s 

4 percent efficient DSSCs are among the highest efficiency 

inkjet printed DSSCs in the world, there are still numerous

gains to be made by optimizing the ink design and printing processes (Ref. 39). 

The ink used by UofL to conduct their preliminary device 

fabrication trials and to develop printing strategies for the 

smooth nonporous substrates like fluorine-doped tin oxide 

(FTO) glass, conductive plastics, and stainless steel that are 
NASA/TM—2015-218866 8 

likely to be used in industrial DSSC fabrications was unsuited 

for long term use and was determined to ultimately be the cause 

of the reduction in fill factor as seen in the IV curve of the nominally 15 μm 12 layer cell in Figure 10. This is due to a smaller 

than ideal titanium dioxide or titania (TiO2) nanoparticle size, 

uneven drying forcing the use of many thin layers and heat 

treatment cycles resulting in larger crystallite sizes and decreased porosity in the lower layers, and low overall porosity 

due to lack of a structure directing agent combined with the 

small particle size preventing dye absorption. To improve device efficiency and move towards industrially viable inks, our 

research has focused on developing TiO2 inks from the relatively inexpensive P25 nanopowder that are suitable for printing and designed to rectify the issues in the previous ink. 

For an ink to be suitable for printing with the Dimatix DMP 

and related print heads, it must be stable for at least 24 h to 

prevent particle agglomeration and nozzle clogging during printing, have a pH of 6-8 to prolong print-head life, have a surface 

tension in the 28 to 32 mN/m2 range, a viscosity in the 6 to 12 cP 

range, good drop formation, deposit the suspended TiO2 as 

evenly as possible, and preferably use relatively non-toxic solvents. These requirements eliminated all of the traditional TiO2

colloidal dispersions due to their pH or use of large polymers. 

Two dispersions were produced with traditional bead milling 

techniques, a 5 wt% TiO2 1:2 1-butanol: cyclohexanol that was 

designed to air dry thin layers quickly and an extremely environmentally friendly 10 wt% TiO2 60:33:7 water:glycerol:1-butanol 

dispersion using 1 mM Na4P2O7 and 1 wt% ZetaSperse-1200 to 

improve dispersion stability. Initial tests of these dispersions indicate much better dye absorption than the previous inks (see 

Figure 11); UofL anticipates that efficiencies of cells made from 

these dispersions should improve accordingly.

 

Figure 10.—(Left) Complex cell structure with sub 200 μm grid lines printed with DMP2800 

printer on TiCl4 treated, O2 plasma treated 316 Stainless Steel; (Right) IV curve of cells of increasing thickness printed from 10 wt% TiO2 2:1 H2O:glycerol ink with 1 percent Triton 100X.

Figure 11.—Left to right: Dysol Paste; Old pH = 2 aqueous ink with 15 nm TiO2; new aqueous ink.
NASA/TM—2015-218866 9 

3.2 Iodide-Free Dye-Sensitized Solar Cells 

Using Nanowire-Based Architectures

In this study, the UofL group found that the performance of 

DSSCs can be improved by engineering the electron dynamics 

and surface properties of the semiconductor photoanode. We 

find that TiO2 nanoparticles coated tin oxide nanowires yield 

DSSCs with ten times higher short-circuit current density than 

the widely employed TiO2 nanoparticle, even when a commercially available ruthenium dye is used for sensitization. State of 

the art work in literature on improving the performance of 

DSCs using alternate redox electrolytes have only focused on 

using new organic dyes instead of the conventional Ru based 

dyes. Analysis of the literature data showed that Ru based dyes 

have higher reorganization energies compared to organic dyes 

and hence Ru based dyes are associated with high driving forces 

for dye-regeneration (Ref. 40). No attention has been paid to 

engineering the photoanode architecture for improving the performance with alternate redox electrolytes. 

Prior studies using tin oxide nanowires in conjunction with 

iodide/triiodide redox electrolyte has shown that tin oxide nanowires have two orders of magnitude higher electron lifetimes 

and fast electron transport properties when compared to titania 

nanoparticles. In this study, the electron transport and recombination properties of different architectures involving nanoparticles, nanowires and nanoparticle/nanowire hybrid architectures 

of tin oxide and titania are compared to gain insight into the 

factors that contribute to the improved performance when 

alternate redox couples such as ferrocene/ferrocenium 

(Fe(C5H5)2/Fe(C5H5)2

+) or heterocyclic (2,2,6,6-tetramethylpiperidin-1-yl)oxy and the cation species (TEMPO/TEMPO+) are 

used (Ref. 41). 

The location of surface traps states and their passivation was 

found to have a significant impact the electron dynamics and 

photovoltaic characteristics of the DSC. The trap states in tin 

oxide nanowires are located very close to the conduction band 

(0.071 eV) when compared to titania nanoparticles that have 

much deeper trap states (0.24 eV). The shallow trap state in tin 

oxide nanowires allow faster detrapping of the electrons from 

the trap resulting in improvement of electron lifetimes over 

titania nanoparticles. In addition, the high diffusion lengths in 

tin oxide nanowires thicker photoanode films when alternate redox electrolytes are used thereby allowing increased sensitizer 

loading and light harvesting. Ongoing work is focused on new 

absorbers for achieving higher efficiencies (Figure 12). 

Figure 12.—(Top) Current-voltage characteristics of the TiO2

NP/SnO2 NW hybrid architecture and TiO2 NP based DSCs

with ferrocene and TEMPO redox electrolytes; (Bottom)

SnO2 NW/TiO2 NP hybrid architectures.

3.3 Lower-Temperature Fabrication of 

Multiwalled Carbon Nanotubes

The unique mechanical and electronic properties of both single-walled and multiwalled varieties of carbon nanotubes have 

proven to be a rich source of new physics and have led to applications in a wide variety of materials and devices(Ref. 42). From 

an applications perspective, multiwalled carbon nanotube 

(MWNT) science and technology has developed rapidly since 

their discovery due to unique properties including high surface 

area, high mass-specific strength, controllable electronic properties, and thermal and chemical stability (Refs. 36, 37, and 42). 

Characteristic of MWNTs are the concentric graphene layers 

spaced 0.34 nm apart, with diameters from 10 to 200 nm and 

lengths up to hundreds of microns.

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4 Tempo - SnO2

 NW/TiO2 NP hybrid

 Ferrocene - SnO2

 NW/TiO2 NP hybrid

 Tempo -TiO2 NPs

 Ferrocene -TiO2 NPs

Current density, mA/cm2

Voltage, V

 

 

 

 
NASA/TM—2015-218866 10

Carbon nanotubes (and recently graphene) are showing tremendous promise in improving the performance of power 

devices, such as thin film polymeric solar cells (Ref. 3) or electrochemically-based technologies (Ref. 36) such as directmethanol fuel cells, lithium-ion (Li+) batteries, and ultracapacitors. In many of the power applications, the carbon nanotubes 

are used in concert with other materials often as a composite 

thin film (Ref. 3). Garnering control over the properties of both 

the carbon nanotubes and the resulting composites is an important step towards realizing device optimization. 

Thus, a low-cost, simple MWNT production process is an important enabling technology. Preferential oriented MWNTs at 

GRC were prepared by injection chemical vapor deposition 

(CVD) using an organometallic iron catalyst in toluene (see 

Figure 13) (Ref. 43). The concentration of the catalyst was 

found to influence both the growth (i.e., MWNT orientation) of 

the nanotubes, as well as the amount of iron in the deposited 

material (Ref. 36). Nanotubes were characterized by a variety 

of characterization techniques; as deposited, MWNTs contained as little as four weight percent of iron (Figure 14). This 

synthetic route provides a simple and scalable method to 

deposit MWNTs with a low defect density, low metal content 

and a preferred orientation (Figure 15) (Ref. 3). 

Figure 13.—Schematic (top) and picture (bottom) of an atmospheric-pressure hot-wall spray pyrolysis reactor. 

Figure 14.—Characterization data ensemble of MWNTs, clockwise from upper left: 

SEM, TGA, TEM, and Raman.

20 nm
NASA/TM—2015-218866 11

Figure 15.—Scanning electron micrograph of chemical vapor 

deposited multiwall carbon nanotube array on indium tin 

oxide coated glass. Inset: high-resolution micrograph of the 

multiwall carbon nanotubes.

4.0 Wide-Bandgap Semiconductor 

Materials for High-Power Devices

Silicon carbide (SiC) materials, processing, and device technologies occupy a critical space in wide bandgap semiconductors for harsh environments (Ref. 44). However, the poorly 

understood electrical influence of existing defects in SiC epitaxial layers is the bottleneck in the reliability of systems that 

use SiC devices. This lack of reliability has stymied the adoption of SiC devices by systems-integrators in industry, despite 

the various transformational systems level benefits they offer 

over silicon, such as higher speed, smaller payload, and higher 

efficiency. Work continues at and GRC (Ref. 45) and the University of South Carolina (USC) (Ref. 46) to improve prospects 

for SiC power devices and sensors, by gaining detailed physical 

insight into the statistical influence of defects, as was done with 

gallium nitride (GaN) technology for LED applications 

(Ref. 47), but remains unexplored with SiC.

4.1 State-of-the-Art SiC Homoepitaxy 

The group at GRC has a long track record of developing various growth methods including CVD to grow several polytypes 

of SiC, particularly hexagonal materials, and to use these materials for the fabrication of various devices, including sensors, 

detectors, etc. (Ref. 48). One goal of processing hot wall chemical vapor deposition (HW-CVD) 4H-SiC using novel substrates is to dramatically reduce the concentration of defects to 

enable the fabrication of high-power devices. We briefly consider several relevant processing parameters (Table I) that are 

adjustable when growing SiC by HW-CVD, including: substrate type, growth temperature, chemical precursor(s) for Si 

and C, flow rate, pressure, composition of gases, and pre-/postdeposition treatment(s) (Refs. 49 to 52). Potential insights to be

Figure 16.—X-ray rocking curve for a 60 μm thick SiC epitaxial layer grown at USC, with FWHM < 10 arcsec. 

gained from characterizing the resultant films are related to 

polytype(s), defect(s) and density, and measurable electrical parameters. As discussed below, the group at USC has had some 

success by employing halogen-containing precursors for reducing the defect density in 4H-SiC with improved subsequent device performance. The group at USC has demonstrated 

extremely high quality 4H-SiC homoepitaxy on 8° off-axis substrates at growth rates as high as 108 μm/h using chlorine and 

transformational F-based chemistries (Refs. 52 and 53). The 

USC group has migrated to 4° and 1° substrates (Refs. 54 and 

55). These high growth rates, essential for the commercialization of high voltage (> 10 kV) SiC power devices, have been 

obtained without sacrificing material quality. Surface morphologies are specular (Ref. 56), with doping concentrations 

< 1013cm–3 (Ref. 53), x-ray rocking curve widths < 10 arcsec 

(Figure 16) and carrier lifetimes >2 μs. Defect analysis reveals 

dislocation densities < 2000 cm–2 being achieved routinely, 

comparable to, or better than, the state of the art in industry 

(Refs. 52 to 56), enabling the systematic defect isolation in 

small devices is described below. This capability was the result 

of Office of Naval Research (ONR) funded research at USC. 

4.2 Etching and CVD Growth of 4H-SiC: 

Modeling of Surface/Small Molecule

Interactions

To expedite development of low-defect 4H-SiC for highpower devices, it is critical to reduce the density of 3C-polytype 

growth-induced defects. While a vigorous HW-CVD growth effort is underway to utilize advanced substrate materials to produce such material, it is a time-consuming effort that could 

potentially be facilitated by getting some insights via first 

600 nm

100 μm
NASA/TM—2015-218866 12

TABLE I.—CVD PROCESSING PARAMETERS AND RESULTS RELEVANT TO (4H-)SiC GROWTH

Substrate Conditions Precursor(s) Results Issue(s) Reference

8° off-axis towards

[11-20]

140 torr, 1300 °C, 

C/Si = 6, H2 = 8 slm 

(carrier gas)

CH3Cl, SiCl4 At growth rates above 5 to 6 μm/h 

process window for good-quality 

low-temperature growth becomes 

too narrow

Triangular defects from formation 

of Si droplets in the gas phase

49

8° and 2° off-axis 

towards

[11-20]

150 to 400 torr, 

1300 to 1450 °C, 

C/Si and H2 = variable

CH3Cl, SiH4 (3% in H2) EA = 0.57 eV for Si cluster formation/ evaporation

Si cluster nucleation in the gas 

phase

50

[0001] on-axis and

8° off-axis towards

[11-20]

50 to 250 torr, 1400 to 

1850 °C, C/Si (variable) 

and H2 = 5 slm

C3H8, SiCl4 Growth-assisted etching was developed; hillock-like pits show 

distribution of micropipes

Mirror-like finish but over 1850 °C, 

uncontrolled etching

51

[0001] 8° off-axis 

towards

[11-20]

300 torr, 1550 °C, C/Si 

(0.9 to 1.7) and H2 = 6 to 

12 slm

C3H8, SiH2Cl2 High growth rate (up to 

100 μm/h) attained in chimneytype HW-CVD reactor

No observable in-grown 3C-SiC inclusions or other morphological defects – eliminate Si cluster 

formation

51

TABLE II.—EXAMPLES OF PRIOR FIRST PRINCIPLES STUDIES RELATED TO SILICON CARBIDE 

Topic studied Method(s) used Conclusions Reference

Energetics of the most common 

SiC polytypes

Density functional theory (DFT) on CASTEP

with the PW91 generalized gradient approximation (GGA) functional together with ultrasoft 

pseudopotentials

Energy differences among SiC polytypes are enhanced at the 

surface with respect to the bulk

57

4H–SiC(0001) and (000-1) surface processes at 1600 °C and 

2300 °C

Combined Molecular dynamics (MD)/DFT calculations using CASTEP codeH abstraction reactions were slightly exothermic or endothermic 

with the order of energies: H < Br < Cl <F 

58

Substitutional impurity atoms 

in 4H-SiC

Plane-wave pseudopotential method implemented 

in Vienna ab initio simulation package (VASP) 

based on DFT

Impurity atoms N, O, S substitute on C sites; B and Se depend 

upon the composition and growth conditions; all others (Be, 

Mg, Al, P, Zn, Ga, As, Cd, In, Sb, Te) substitute on Si sites

59

Electrically active defects of 

4H-SiC

MD (Tersoff) and DFT with local-density approximation (LDA) implemented in VASPNative (or intrinsic) point defects of SiC are electrically active 

and have energy levels within the band gap of 4H-SiC. While it 

is possible to passivate Si vacancies using atomic hydrogen, C 

vacancies cannot be passivated in a similar way

60

principles modeling studies. Several examples of prior activity 

by other groups and published in the literature are listed in 

Table II (Refs. 57 to 60). 

When considering theoretical methods to facilitate determination of improved processing parameters for HW-CVD to produce low defect (< 1016 defects/cm3

) 4H-SiC, there are two 

approaches to consider: shareware/freeware or commercial 

packages. Below we provide a literature background, briefly 

mention some preliminary results on a related, relevant system 

and discuss potential directions moving forward. While 

Table II is certainly not an exhaustive list, it points to several 

areas of processing space that are potentially amenable to first 

principles modeling and subsequent analysis of SiC growth: 

polytype stabilities, surface processes, substitutional impurity,

atom chemistry, and electrically active-defect formation.

As is clear from Table II, one approach for determining the 

most energetically stable configuration for atoms in a solidstate structural sense entails a combination of methods. Combining aspects of density functional theory (DFT) and Newtonian molecular dynamics (MD) will lend some insights into the 

most probable chemical species that exist on the surface and in 

relevant more energetic domains in the bulk of the growing 

crystal. Commercial codes, while expensive, facilitate the combination of methods to address complex problems. Academic 

and/or freeware codes are inexpensive but often have minimal 

support or documentation; also combining methods requires 

transfer of data sets across software platforms with inherent 

complexities and inefficiencies.

An approach being employed at Florida A&M University 

(FAMU) involves numerically simulating a system using nonlinear partial differential equations. A recent FAMU publication describes a novel modeling approach for an atomic layer 

deposition (ALD) process involving the first comprehensive 

numerical solution of the Dusty-Gas Model (DGM) and included a complete binary diffusion term (BDT) (Ref. 61). The 

purpose of this model was to predict the concentration of the 

reactant gases at the wafer. A one-dimensional model was constructed using mass conservation and dimensional analysis. 

FAMU introduced an explicit-implicit scheme to solve the 

DGM. After linearizing the equations, an implicit scheme 

(BDT) produced a program that solves the full DGM and is unconditionally stable (Ref. 61). 
NASA/TM—2015-218866 13

A concentration-dependent Damkohler number relevant to 

the purge step of the process was derived. The simulation 

matched the experimental data at a specific Damkohler number 

and further variation of the parameter confirmed existing experimentally observed phenomena (Ref. 61). Our current plan is to 

extend this model to two dimensions to simulate flow across 

and around a SiC substrate in a HW-CVD reactor. Insights from 

modeling reported in the literature will be utilized to inform our 

choice of parameters and interpretation of and correlation with 

experimental results. 

4.3 SiC Device Fabrication and 

Characterization: Isolating or Reducing 

Impact of Defects 

With lower defect epitaxy demonstrated (Figure 17), the 

group at USC is currently fabricating diodes using their demonstrated processes on material grown on various off-cuts of SiC; 

this would allow for isolating single defects in individual unipolar Schottky and bipolar p-i-n diodes. USC will focus on single and compound basal plane dislocations (BPD’s), threading 

edge and screw dislocations (TED’s, TSD’s), step bunching, 

along with other important defects that may emerge (Figure 18) 

(Refs. 52 to 56, and 62 to 64). 

While crystal growers typically attempt to eliminate all defects, this is not a tractable solution, as there are inevitably 

tradeoffs; i.e., basal plane dislocations vs. screw dislocations in 

SiC. However, if the electrical influence of the defects is 

known, crystal growers can tackle the more disruptive ones, 

while they can tolerate less severe defects. By correlating the

electrical performance with the defect profile of devices in a 

statistical fashion, the electrical role of individual defects can

Figure 17.—Electron beam induced current-SEM 

images of Schottky diodes 70 μm in diameter 

containing (top) single and (bottom) two defects 

in active region.

Figure 18.—(Left) Static reverse breakdown I-V curves of an ensemble of commercial Schottky diodes characterized at USC. The 

large scatter in the performance shows the clear influence of defects; (Middle) SEM of typical KOH etched defects in SiC epitaxial 

layers; (Right) Dynamic evolution of stacking faults from a BPD under 200/cm2 stress in a SiC bipolar pin diode at USC. The systematic connection between these factors has never been investigated and represents the key bottleneck to SiC device adoption 

by systems integrators.
NASA/TM—2015-218866 14

be isolated. Post-deposition etching is one approach to “managing” acceptable defect levels to improve device performance.

Finally, besides use of modeling to improve quality of grown 

materials, it is feasible to model device performance analytically and with physics-based finite element tools to understand 

the physical origin of defects and their influence on device performance. Alternatively, it is certainly reasonable to propose 

developing physics-based circuit models for devices with multiple defects, to be incorporated into larger systems level simulations. These models will be tested on large devices with 

multiple defects to be able to “reverse-engineer” the defect profile of a given device based on its electrical characteristics. As 

noted above, the next generation of SiC devices has great potential for dual-use applications in diverse fields such as biomedicine, aerospace and defense, engines, and energy. The next 

section continues this theme for several other promising processing, materials and device technologies. 

5.0 Dual-Use Applications of Novel

Processing, Materials, and Devices

We begin this section with several intriguing applications of 

photovoltaics for space exploration in two quite different size 

regimes that speak to the need for numerous solutions to the 

problems posed by the need to provide reliable power. An innovative approach to intelligent systems design is the subject of 

the second subsection that describes the concept, design, and 

testing of an integrated power device in low Earth orbit (LEO). 

The essence of dual-use applications is the ability to repurpose 

technology designed to withstand the rigors and challenge of 

the space environment for terrestrial situations that present similar problems and issues, though perhaps not in a simultaneous 

fashion. Another important aspect of the GRC effort that should 

certainly not be overlooked is the variety of individual collaborations fostered, organizational partnerships formed, and students educated and brought into the aerospace community as a 

result of the technical work. The final section gives an explicit 

example of an educational tool derived from a NASA-driven 

power material need and solution. 

5.1 Space Exploration and Science Enabled by 

Advanced Materials and Devices

An obvious application for advanced high performance photovoltaics technology is to enable interplanetary travel in the 

solar system via solar electric propulsion (SEP); solar arrays 

provide the power for various electric propulsion engines. For 

example, NASA’s Dawn spacecraft combines innovative stateof-the-art technologies pioneered by other recent missions with 

commercial and repurposed components (Ref. 65). With its solar array in the retracted position (for launch), the Dawn spacecraft is approximately 7 ft long; with its wide solar arrays 

extended, Dawn expands to a length of 65 ft (Figure 19). Dawn 

was launched in September 2007 and spent nearly 14 months 

orbiting Vesta, the second most massive object in the main

Figure 19.—This artist's concept shows NASA's Dawn spacecraft heading toward the dwarf planet 

Ceres. Dawn spent nearly 14 months orbiting Vesta, the second most massive object in the main 

asteroid belt between Mars and Jupiter, from 2011 to 2012. It is heading towards Ceres, the largest 

member of the asteroid belt. When Dawn arrives, in February 2015, it will be the first spacecraft to 

go into orbit around two destinations in our solar system beyond Earth. (NASA/JPL-Caltech)
NASA/TM—2015-218866 15

asteroid belt between Mars and Jupiter, from 2011 to 2012. It is 

heading towards Ceres, the largest member of the asteroid belt. 

When Dawn arrives, in February 2015, it will be the first spacecraft to go into orbit around two destinations in our solar system 

beyond Earth.

On the other end of the spacecraft size spectrum are CubeSats, 

a class of small satellites that roughly fall into the “nanosatellite” 

regime. They are based upon a standard form factor of 10 cm 

(~ 4 in.) on a side. Thus a one-unit (1U) CubeSat has a volume of 

1000 cm3 or 1 liter. Other standard sizes include 2U (2x1U), 3U 

(3x1U), and 6U (3x2U). The sizes reflect standard delivery pods 

to launch CubeSats from a variety of platforms; 3U is currently 

the most typical CubeSat size. Currently for launch safety, the 

maximum mass guidance for a CubeSat is 1.33-2 kg/U. As a consequence of the reasonable (low) cost and opportunity for learning to be derived from participation in CubeSat missions, many 

CubeSats that have been designed, built, and flown are affiliated 

with an institution of higher learning. An excellent recent and updatable review on the state of the art of small spacecraft technology, with an emphasis on CubeSats has been published by our

colleagues at the NASA Ames Research Center and includes a 

significant amount of information on relevant technologies as 

well as the legacy of small satellite (~20 percent CubeSat) missions from the past 15 years (Ref. 66). 

We recently developed a concept using a parametric spacecraft assessment study for a mission to a diminutive asteroid 

(DAVID) in the latter half of 2019, given an opportunity for 

inclusion of a 6U CubeSat on the Space Launch System Exploration Mission-1, currently projected for a December 17, 2017 

launch. The core of the science payload for this proposed mission would be based upon advanced SiC radiation sensors enabled by the device development technologies described above. 

Figure 20 shows a diagram of the 6U CubeSat with a block system diagram as well as several candidate device architectures 

Figure 20.—(Top) Schematic and systems diagram of DAVID, a 6U CubeSat designed to rendezvous with 

an asteroid; (Bottom) Architectures of two SiC-based devices to provide radiation detection capabilities 

for instruments to be integrated into DAVID or other CubeSats.

Subsystems:

Electric Propulsion

Attitude Determination and Control

Command and Data Handling

Communications

Electrical Power

Science

Structures
NASA/TM—2015-218866 16

Figure 21.—Starshine 3 nanosatellite; inset: close-up of an 

IMPS surrounded by six commercial triple-junction III-V solar 

cells. 

(Ref. 66). Finally, it is interesting to note that travel from a 

trans-lunar orbit to the destination asteroid is also provided by 

SEP technology, albeit much smaller than Dawn. To briefly 

summarize, the CubeSat format during the brief period of its 

development has demonstrated great value as an educational 

paradigm as well as an intriguing low-cost platform for advanced technology demonstration for LEO and beyond.

5.2 Integrated Power Technologies

GRC has been working to develop lightweight, integrated 

space power systems on small or flexible substrates. These systems generally consist of a high efficiency thin film solar cell, 

a high energy density solid-state lithium-ion battery, and the associated control electronics in a single monolithic package. 

These devices can be directly integrated into microelectronic or 

MEMS devices and are ideal for distributed power systems on 

satellites or even the main power supply on a nanosatellite 

(Ref. 68). These systems have the ability to produce constant

power output throughout a varying or intermittent illumination 

schedule as would be experienced by a rotating satellite or 

“spinner” and by satellites in a LEO by combining both generation and storage. An integrated thin film power system has the 

potential to provide a low mass and cost alternative to the 

current SOA power systems for small spacecraft. Integrated 

thin film power supplies simplify spacecraft bus design and reduce losses incurred through energy transfer to and from conversion and storage devices. It is hoped that this simplification 

will also result in improved reliability.

GRC developed and flew an integrated microelectronic 

power supply (IMPS) for a space flight experiment in conjunction with the Project Starshine atmospheric research satellite 

(see Figure 21) (Ref. 69). This device integrates a seven 

junction small-area GaAs monolithically integrated photovoltaic module (MIM) with an all-polymer LiNi0.8Co0.2O2 lithiumion thin film battery. The array output is matched to provide the 

necessary 4.2 V charging voltage and minimized the associated 

control electronic components. The use of the matched MIM 

and thin film Li-ion battery storage maximizes the specific 

power and minimizes the necessary area and thickness of this 

microelectronic device. This power supply was designed to be 

surface mounted to the Starshine 3 satellite, was ejected into a 

LEO with a fixed rotational velocity of 5° per second after 

launch from Kodiak, Alaska, on September 30, 2001. The satellite de-orbited on January 21, 2003, after 7,434 revolutions 

around the Earth. The IMPS successfully provided continuous 

power even with the intermittent illumination due to the satellite 

rotation and LEO. Data from the 2 weeks of testing indicated 

that the Sun-facing supply maintained a voltage in the range of 

2.8 to 2.9 V from initial reading of 2.65 V; for IMPS charged 

mainly by Earth’s albedo, the comparable readings were a range 

of 2.55 to 2.65 V from initial reading of 2.5 V. 

Finally, as power-integrated (or integrated-power) devices 

and systems are designed, fabricated, and successfully tested, 

utilization across a range of applications can be anticipated. A 

typical method for technology transfer involves patenting and 

licensing new inventions and handing off inventions to the private sector for further development. An example of intellectual 

property (IP) resulting from a collaboration on a solar cell/battery device with and industry and a not-for-profit entity 

(Ref. 70). The resulting patent issued several years ago is 

owned by Aerospace Corporation and is currently under negotiation for licensing by the private sector. Other examples of 

technology transfer are discussed in the following section.

5.3 Technology Transfer to Facilitate 

Nanotechnology Research and Education 

As discussed in several examples above, advanced (nano)materials, processing, and the devices that they enable have numerous potential dual-use applications. The multiyear effort on 

developing and utilizing single-source precursors for I-III-VI2

thin film- and nanomaterials produced significant IP that was 

patented and is currently jointly owned by GRC and the Ohio 

Aerospace Institute (OAI) (Ref. 71). Several companies have 

negotiated a license for the technology but at this time, no 

agreement has been reached. An earlier example of a related 

technology resulted in the formation of a small business. CVDdeposited gallium sulfide passivates gallium arsenide (GaAs) 

and improves the performance of several classes of GaAs devices (Refs. 72 and 73) Gallia, Inc. was formed in Weston, Massachusetts, to commercialize this technology (Refs. 74 and 75). 

After several years of operation, TriQuint Semiconductor 

(www.triquint.com/) of Hillsboro, Oregon, purchased 
NASA/TM—2015-218866 17

Figure 22.—Nanotech Innovations LLC’s commercially available MWNT production reactor, SSP-354.

Gallia, Inc., and all rights to the technology. It is anticipated that 

NASA will eventually utilize these technologies in commercial 

off-the-shelf (COTS) products. 

Because GRC was more interested in the power technologies 

that could result from the incorporation of carbon nanotubes, 

and not in the actual production of the carbon nanotubes themselves, the Center released the IP to the inventors in 2005

(Ref. 43). Subsequently, this technology has been transferred to 

Nanotech Innovations LLC (NTI) in Oberlin, Ohio (Ref. 76).

For several years, the company had focused on improving the 

device. In 2010, NTI was awarded a patent for the process and

apparatus to grow high quality, low-impurity carbon nanotubes. 

A portable, bench-top system, called the SSP-354 (Figure 22), 

can make research-scale quantities of high quality nanotubes 

within just a few hours. A major advantage of the NASAderived technology is that it is a single-step process; the user 

simply loads the injector and presses start. Currently, the machine is supporting the incorporation of carbon nanotubes into 

education curricula, research, and product-development endeavors for small-scale applications (Ref. 77). 

6.0 Conclusions: Lessons Learned and 

(Other) Terrestrial Applications

On Earth, the need for alternative energy is a high priority 

given the constant increase in worldwide population and despite 

recent advances in exploiting such resources, the fact that fossil 

fuel reserves are finite. For important applications involving 

terrestrial uses, price per watt will clearly be a critical driver. 

Conversely, the challenges of aerospace and defense have 

spurred the development of advanced technologies. These 

challenges can be addressed by a variety of technologies that 

overcome issues involving available area, efficiency, 

reliability, and specific power at an optimal cost. The particular 

application may be in aerospace, defense, utility, consumer, gridbased, off-grid, recreational, or industrial settings. Organic-based 

photovoltaics will most likely provide solutions in applications 

where price and/or large area challenges dominate such as consumer or recreational products. Inorganic materials will most 

likely predominate in aerospace and defense uses: satellites, nonterrestrial surface power, and planetary exploration.

The inclusion of nanocrystalline materials in photovoltaic devices has been proposed as a means to improve the efficiency 

of photon conversion (quantum dot solar cell), enable low-cost 

deposition of thin-films, provide sites for exciton dissociation, 

and pathways for electron transport. A promising method to circumvent the formation of undesirable reaction products involves the use of single-source precursors, small molecules that 

include all the elements required in the final material. These 

precursors can be designed with many properties in mind including stoichiometry, solubility, and volatility. The widebandgap, semiconducting material ZnO has received significant 

attention recently due its many outstanding properties; it is used 

for a wide array of applications including photovoltaics and 

photocatalysis. The performance of DSSCs can be improved by 

engineering the electron dynamics and surface properties of the 

semiconductor photoanode. From an applications perspective, 

MWNT science and technology has developed rapidly since 

their discovery due to unique properties including controllable 

electronic properties and stability. New generation solar cells 

based on nanostructured materials promise to enhance light harvesting efficiencies, greatly increasing their utility for future 

energy needs.

The poorly understood electrical influence of existing defects 

in SiC epitaxial layers is a critical bottleneck in the reliability 

of systems that use SiC devices. This lack of reliability has stymied the adoption of SiC devices by systems-integrators in industry, despite the various transformational systems level 

benefits they offer over silicon, such as higher speed, smaller 

payload, and higher efficiency. The next generation of SiC devices has great potential for dual-use applications in diverse 

fields such as biomedicine, aerospace and defense, engines, and 

energy.

Advanced high performance photovoltaics technology enables interplanetary travel in the solar system (i.e., NASA’s

Dawn spacecraft) via SEP; solar arrays provide the power for 

various electric propulsion engines. For example, combines innovative state-of-the-art technologies pioneered by other recent 

missions with commercial and repurposed components. On the 

nanosatellite (spacecraft) end of the scale, the CubeSat format 

during the brief period of its development has demonstrated 

great value as an educational paradigm as well as an intriguing 
NASA/TM—2015-218866 18

low-cost platform for advanced technology demonstration for 

LEO and beyond.

An integrated thin film power system has the potential to provide a low mass and cost alternative to the current SOA power 

systems for small spacecraft. Integrated thin film power supplies simplify spacecraft bus design and reduce losses incurred 

through energy transfer to and from conversion and storage devices. It is hoped that this simplification will also result in improved reliability. As power-integrated (and other advanced) 

devices and systems are designed, fabricated, and successfully 

tested, utilization across a range of applications can be anticipated. A typical method for technology transfer involves patenting and licensing new inventions and handing off inventions to 

the private sector for further development. Other more creative 

partnerships and collaborations will at times be necessary to 

break down institutional barriers.

The essence of dual-use applications is the ability to repurpose technology designed to withstand the rigors and challenge 

of the space environment for terrestrial situations that present 

similar problems and issues, though perhaps not in a simultaneous fashion. An important aspect of the GRC effort that should 

certainly not be overlooked is the variety of individual collaborations fostered, organizational partnerships formed, and students educated and brought into the aerospace community as a 

result of the technical work.

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