Director’s Discretionary 

Research and Development 

Program 

Annual Report 

Fiscal Year 2006 

March 2007 NREL/MP-700-40234 

Contract No. DE-AC36-99-G010337 
Director’s Discretionary 

Research and Development 

Program 

Annual Report 

Fiscal Year 2006 

National Renewable Energy Laboratory 

1617 Cole Boulevard 

Golden, Colorado 80401-3393 

NREL is a U.S. Department of Energy Laboratory 

Operated by the Midwest Research Institute • Battelle 
This report was prepared as an account of work sponsored by an agency of the United States 

government. Neither the United States government nor any agency thereof, nor any of their employees, 

makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, 

completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents 

that its use would not infringe privately owned rights. Reference herein to any specific commercial 

product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily 

constitute or imply its endorsement, recommendation, or favoring by the United States government or any 

agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect 

those of the United States government or any agency thereof. 

 Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste 
2006 DDRD Annual Report 

Table of Contents 

Introduction........................................................................................................4 

NREL Mission ....................................................................................................4 

Program Overview ............................................................................................4 

DDRD Management Process ...........................................................................6 

2006 DDRD Portfolio .........................................................................................6 

Portfolio Highlights ...........................................................................................8 

Project Summaries ...........................................................................................9 

Integrated Systems ................................................................................................................................................9 

Renewable Electricity Science and Technology................................................................................................11 

Renewable Fuels Science and Technology........................................................................................................28 

Appendix A. Acronyms and Symbols............................................................35 

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2006 DDRD Annual Report 

INTRODUCTION 

NREL Mission 

The National Renewable Energy Laboratory’s (NREL) mission is to: develop renewable energy 

and energy efficiency technologies and practices, advance related science and engineering, and 

transfer knowledge and innovations to address the nation’s energy and environmental goals. 

Program Overview 

NREL has supported scientifically innovative and analytically creative concepts through the 

Director’s Discretionary Research and Development (DDRD) Program from 2000 to 2006. At the 

end of FY 2006, the DDRD Program made a transition to the Laboratory Directed Research and 

Development (LDRD) Program as directed by the 2006 Energy and Water Appropriations Act. 

This ACT enables the Secretary of Energy to authorize, at DOE-owned, contractor operated 

laboratories, an amount not to exceed 8% to conduct LDRD programs. The Act made NREL 

eligible to participate in the LDRD program. So, with the concurrence of DOE, NREL closed out 

its DDRD program at the end of fiscal year 2006; thus, this represents the final report on the 

DDRD program. 

$0

$200,000

$400,000

$600,000

$800,000

$1,000,000

$1,200,000

$1,400,000

$1,600,000

$1,800,000

$2,000,000

Renewable Fuels Renewable Electricity Strategic Analysis Integrated Systems Mgmt

Figure 1. DDRD 2006 Technical Breakdown.

4 
2006 DDRD Annual Report 

The NREL DDRD program comprises projects that strengthen NREL’s four technical 

competencies: Integrated Systems, Renewable Electricity, Renewable Fuels, and Strategic 

Analysis. The majority of the 2006 funds were used for innovative projects in renewable 

electricity, as shown in Figure 1. Program management costs are also included. 

R&D Expertise 

NREL's focused R&D capabilities are positioned to advance national energy goals by 

developing innovations to change the way we power our homes, businesses, and cars. 

NREL's R&D areas of expertise are: 

Renewable electricity — solar, wind, biomass, geothermal 

Renewable fuels — biomass, hydrogen 

Integrated energy system engineering and testing — buildings, 

electric systems, and transportation infrastructures 

Strategic development and analysis — economic, financial, 

 and market analysis, planning and portfolio prioritization 

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2006 DDRD Annual Report 

DDRD Management Process 

The DDRD program is managed by the Laboratory Development Office (LDO), within the 

Strategic Development and Analysis (SD&A) directorate. The LDO functions center on the 

strategic planning and development for the Laboratory. The program administrator for the DDRD 

process ensures Laboratory adherence to the guidance laid out in DOE Order 413.2B, and 

provides regular feedback to executive management on the status of the program including 

individual project reports when necessary. The table (above) shows that DDRD program 

management consumed only 2% of the overall DDRD budget, including time charged by peer 

reviewers for feedback on proposals reviewed during the Call for Proposals and the cost of 

producing the annual report. 

2006 DDRD Portfolio 

Portfolio Funding 

In FY2006, NREL had an approved DDRD program budget of $3,216,004. Projects spent 

$2,948,725, and program management consumed $114,561. The cost of proposal peer reviews 

was $15,974. Adjustments were made for projects that ended in FY2005 but incurred costs in 

FY2006; the total for those adjustments is ($15,934). The final amount spent was $3,063,326 

(Table 1). 

The FY2006 Energy and Water Appropriations Act authorized the eligibility of all laboratories for 

LDRD funding beginning in FY2006. Conference Report, HR109-275 (which accompanies the 

ACT) required implementation of the accounting changes in FY2006 to apply overhead charges 

to these activities, consistent with cost accounting practices for direct funded program activities. 

In response to the Act and Congress, the DOE CFO directed all laboratories to implement the 

required accounting changes. NREL responded to the requirement, adding the in-house 

overhead (G&A) burden to all DDRD project costs for the fiscal year. NREL’s proposal for a 

transition from the DDRD program to an LDRD program beginning in FY2007 was approved. 

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2006 DDRD Annual Report 

Table 1. FY2006 DDRD Portfolio Funding

2006 Costs

Integrated Systems $125,228

Study of Fundamental Protein/Protein Interactions Involved in Biological Energy 

Generation – Kim, K. 

$125,228 

Renewable Electricity Science and Technology $1,807,431

Shape and Crystallography of III-V Semiconductor Nanoparticles – Ahrenkiel, P $57,502 

Thin-Film Microelectronics for Rapid Gene Expression Analysis – Branz, H. $103,326 

CdMgTe Thin-Films for Light Emitting Diodes – Dhere, R.; Ramanathan, K. $199,874 

Hot-Wire Chemical Vapor Deposition of Metal Oxide Nanorods – Dillon, A.; 

Mahan, H. 

$137,857 

Novel Electron Acceptors for Organic Photovoltaics – Ginley, D. $199,009 

Nanostructured PbTe/PbSe Thermoelectric Materials – Hanna, M. $78,601 

A Critical Examination of the Intermediate Band Concept for Ultra-High Efficiency 

Quantum Dot Solar Cells – Norman, A. 

$209,717 

New Indium-Free Transparent Conductors, Group 3A & 4A Metal Oxide Based 

Materials – Perkins, J.; Ginley, D. 

$259,199 

Photon Emission of Self-Assembled Semiconducting and Quantized Nanostructures 

by Scanning Tunneling Microscopy: Light from the Nanoworld – Romero, M. 

$264,457 

Low Band-Gap Materials for Organic Third Generation Photovoltaics – Shaheen, S. $297,889 

Renewable Fuels Science and Technology $757,795

Localized Carrier Dynamics in Organic Semiconductors Probed via Time-Resolved 

THz Photoconductivity – Ellingson, R. 

$209,850 

Transition Metal Catalysis: Experiment and Theory – Nimlos, M. $193,014 

Pentose Transport and Assay Development – Zhang, M. $164,884 

Fundamental Properties and Application of Novel Crystalline Inorganic-Organic 

Hybrid Semiconductor – Zhang, Y.; Fluegel, B. 

$190,047 

Strategic Analysis $258,271

Prototype Renewable Planning Model – Kroposki, B. $258,271 

DDRD Program Management $114,561

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2006 DDRD Annual Report 

Portfolio Highlights 

In 2006, NREL attained achievements in several areas – many of which resulted in papers being 

presented to journals for publications and papers presented at conferences. 

Advancements were made in understanding the fundamental nature of competitive proteinprotein interactions involved in photobiological energy transduction process. Collaborating with 

computational scientists, Kwiseon Kim’s team was able to improve its understanding of the 

mechanisms governing the protein-protein interactions involved at the metabolic branch point, 

and how protein engineering could tune the metabolic flux between two pathways. Her team is 

preparing a paper for the Biophysical Journal. 

Principal investigators (PIs) Anne Dillon and Harv Mahan produced four papers resulting from 

their project, “Hot-Wire Chemical Vapor Deposition of Metal-Oxide Nanorods”. They have also 

presented at two conferences. Their advancement in nanoparticle deposition encouraged them 

to submit a Record of Invention in the first quarter of 2006. 

David Ginley and his team are working jointly with a team at Sandia National Laboratory on 

“Novel Electron Acceptors for Organic Photovoltaics”. These two teams are working on 

improving hybrid organic photovoltaic (OPV) cells by optimizing nanostructured geometry and 

inorganic-organic interface. This project is new, but is already showing results on the 

development of improved materials for OPV. This technology is well positioned to be incorporated 

into the Solar America Initiative program and to become a competitive thin-film technology. The 

team has submitted three papers and has given talks at a SPIE conference in August. 

Ginley is also working with co-PI John Perkins on “Unconventional Indium-Free Transparent 

Conductors.” In a short time this team has demonstrated that the pulse laser deposited (PLD) 

based Nb:TiO2 films are bulk conductors, that they can be sputtered, that anatase is the critical 

phase and that grain boundaries are important. This is the first time that the original Japanese 

results have been duplicated in any laboratory. This project could have an exceptional impact in 

the PV and electronic display industry. To date, the team has submitted three papers. 

These are a few highlights of the LDRD program. More detail on these and other projects is 

contained in the following sections. 

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2006 DDRD Annual Report 

 

Project Summaries 

Integrated Systems 

Study of Fundamental Protein/Protein Interactions Involved in 

 Biological Energy-Generation 

Principal Investigator: Kwiseon Kim 

FY06 Costs: $125,228 

3⁄4The goal of this study is to address the mechanisms governing competing protein/protein 

interactions involved in photobiological energy-transduction processes and their potential impact 

on in vivo hydrogen production rates via computational modeling.1⁄2

We investigated the fundamental nature of protein-protein interactions involved in photobiological 

energy transduction processes. These can be described as a series of reactions in which 

electrons are transferred between molecular and macromolecular “carriers.” Photochemical 

energy is harvested and stabilized during these processes. In the green alga Chlamydomonas 

reinhardtii, there are two predominant and competing pathways that determine the form in which 

photochemical energy is stored. The first pathway, requiring ferredoxin and FNR association, 

produces starch. The second pathway, requiring ferredoxin and [FeFe]-hydrogenase association, 

produces hydrogen (H2). We use computational modeling to improve our basic understanding of 

the mechanisms governing the protein-protein interactions involved at this metabolic branch 

point, and how protein engineering could tune the metabolic flux between the two pathways. This 

collaboration between biological and computational scientists will identify suitable targets for 

future mutagenesis studies aimed at diverting electron flux towards the H2 production pathway, 

thus increasing H2 production. 

Below is the methodology we used to reach our project goals: 

Protein/Protein Docking Studies. Our initial studies focus on the ferredoxin:hydrogenase 

interaction, keeping in mind that direct mutagenesis of hydrogenase will be the most 

straightforward means to engineer electron flux without disturbing the rest of the metabolism. 

There are no experimental structures of C. reinhardtii hydrogenase, ferredoxin, or complexes. 

We obtained docking complexes using the 3D-Dock package. We generated and scored 10,000 

candidates based on a residue pair potential, and subsequently filtered them by intercluster 

distance. The best candidates were visually screened, and the top two candidate complexes for 

active electron transfer were identified. They are related by an approximate 180o rotation of 

ferredoxin around intercluster axis. The obtained docked complexes are used as input for free 

energy calculations and Brownian dynamics simulations. 

Brownian Dynamics Simulations for Association Rates, Protein Spatial Distributions, and RigidBody Binding Free Energies. We performed Brownian dynamics (BD) simulations of protein 

complexes to compare the association rates between competing hydrogenase-ferredoxin docked 

models. We further obtained the orientational distribution of ferredoxin around hydrogenase to 

verify the efficacy for electron transfer of collision complexes formed during BD. Additionally, we 

calculated binding free energies for rigid protein conformations reflecting the two best candidate 

complexes from empirical docking, labeled by their docking index numbers as “16” and “42”. BD 

simulations using protein conformations from model complex 16 resulted in smaller contact 

distances, larger association rates, and lower free energies than when using complex 42 

conformations. These results support our conclusion that complex 16 represents a better model 

for the active electron transfer complex than 42, based on relative thermodynamic stability from 

free energy calculations. The above data combined with more detailed binding free energy 

9 
2006 DDRD Annual Report 

calculations (below) and electron transfer rate estimates from future quantum mechanical (QM) 

studies will enable us to estimate the H2 production rates for proposed engineered variants. 

Binding Free Energy Calculations. Studies using all-atom molecular dynamics (MD) to calculate 

relative binding free energies of the two competing candidate complexes above were completed. 

To increase the robustness of the calculated energies, electrostatic, non-bonded, and strain 

energy values were averaged over 30,000 dynamics snapshots, each 100 fs apart. In addition, a 

structure averaged over these 30,000 snapshots was used to calculate rigid-body entropic terms 

and solvation energies. This approach should better reflect the energies involved over the 

thermodynamic ensemble. The calculated |ΔΔG| = 20 kcal/mol favoring complex 16. This 

reverses prior results favoring complex 42 as the stronger complex, and reflects the more robust 

approach of averaging over the entire sampled ensemble rather than using a single snapshot 

followed by energy minimization. The result also agrees with Brownian Dynamics simulation 

results to date. 

Correlated Motions of Protein: Engineering Electron Transfer on Molecular Scale. Our team 

analyzed molecular dynamics trajectories of model C. reinhardtii ferredoxin – [FeFe] hydrogenase 

complex. The atomistic MD trajectories generated for binding free energy studies were analyzed 

for correlated motion on an atom-by-atom basis. Intraprotein and interprotein correlations may 

suggest important potential gating elements for electron transfer. 

Electronic Structure of Metalloclusters and Force Field Parameterization. We performed quantum 

chemical studies of the relevant valence states of metalloclusters, and created physically derived 

force parameters of metalloclusters for molecular mechanical (MM) simulations of [FeFe] 

hydrogenase. The current parameterization enables future combined QM/MM studies of [FeFe] 

hydrogenases on: 

• Electron coupling between clusters. 

• Electronic coupling to electrode surface. 

• Active site dynamics and oxygen reactivity. 

We have submitted a manuscript on the atomistic MD free energy calculations to Biophysical 

Journal for review. We are also working on establishing and documenting the method for 

studying protein interactions computationally by molecular docking. Next steps include 

performing BD dynamics simulations of mutant hydrogenases and the ferredoxin, and analyzing 

the trajectories and the docking structures in detail. We will calculate the binding free energies of 

the mutant hydrogenase and the ferredoxin relative to the unchanged forms; perform molecular 

dynamics simulations on the mutant hydrogenases to examine their thermal stability; and study 

the free energy landscape of the hydrogenase-ferredoxin association reaction. 

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2006 DDRD Annual Report 

 

Renewable Electricity Science and Technology 

Shape and Crystallography of III-V Semiconductor Nanoparticles 

Principal Investigator: Phil Ahrenkiel 

FY06 Costs: $57,502 

3⁄4The goal of this work is to demonstrate the viability of transmission electron microscopy (TEM) 

tomography for analysis of individual particle shape and orientation and collective crystallography 

of nanoparticle ensembles.1⁄2

The characterization of particle shapes and ordering in nanoparticle (NP) ensembles is the goal 

of much conventional TEM (Wang, 1998). High-resolution lattice imaging provides 

crystallographic information of individual nanoparticles in two-dimensional (2-D) projection. 

However, analysis of 3-D particle shape from 2-D projections is indirect. Interparticle 

arrangements are usually revealed in relatively low-magnification bright-field images and hollowcone dark-field images, as well as small-angle (large camera length) electron-diffraction profiles. 

For each of these methods, however, a single datum provides only a 2-D sampling of the 

nanoparticle configurations; most three-dimensional (3D) information structural information arises 

by inference. TEM tomography provides a means to merge many individual 2-D images into a 

single, 3-D representation, which can be directly visualized and interpreted for microstructural 

analysis 

Tomographic analysis by reconstruction of TEM tilt series has become an important tool for 

generating 3-D representations of materials in biological sciences. Computed tomography was 

developed in the medical-imaging field, but the concept extends quite naturally to TEM analysis, 

primarily requiring microscope automation, a relatively large sample tilt angle, and sufficient 

computational power. TEM tomography has been less widely explored in materials science, 

because of deleterious diffraction effects from crystalline specimens. 

Bright-field tomography using conventional TEM can provide much useful information on NP 

structure, albeit with less than atomic resolution. We demonstrate successful analysis of NP 

systems using TEM bright-field tomography performed at relatively low magnification under the 

following conditions: 

• A large objective aperture is used 

• A small tilt increment and large tilt range are used 

• The material under study is free-standing and not embedded in a strongly scattering 

matrix. 

The first condition minimizes diffraction contrast. The second condition serves to average out 

intensity variations due to diffraction contrast. The third condition assures that contrast arising 

from the specimen will be positive at all orientations. 

This work demonstrates the feasibility of TEM bright-field tomography for relatively lowmagnification structural analysis of nanomaterials. Tomographic reconstruction by transmission 

electron microscopy is used to reveal three-dimensional (3-D) nanoparticle shapes and the 

stacking configurations of nanoparticle ensembles. Reconstructions are generated from brightfield image tilt series, with a sample tilt range up to ±70°, using single or dual tilt axes. 

Tomography reveals both cubic and hexagonal close-packing configurations in multi-layered 

arrays of size-selected In nanospheres. By lattice imaging and tomography, we relate the 3-D 

shape of PbSe octahedral nanoparticles to the underlying crystal structure. We also confirm cubic 

shapes and simple-cubic packing in multilayers of PbSe nanocubes. The shapes of titanium oxide 

(TiO2 ) nanorod bundles are shown by tomographic reconstruction to resemble flattened 

ellipsoids. 

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2006 DDRD Annual Report 

The stacking of In spheres is an example of success with this technique. In spheres serve as 

catalysts in the colloidal synthesis of nanoparticles, particularly with nanorod and nanowire 

geometries, by solid-liquid-solid reactions. The sphere size provides a means to affect the rod 

diameter. Like most spherical nanoparticles, monolayers of size-selected nanospheres, deposited 

by slow evaporation of solvent on a surface, such as a carbon support film, naturally tend to 

condense into triangular lattices, which are readily identified by their projections in conventional 

TEM bright-field images. When the local coverage exceeds a monolayer, adjacent monolayers 

assemble into 3-D arrays, but the contrast in projected images of these 3-D, ordered regions 

becomes a superposition of contributions from multiple layers, greatly complicating the image 

interpretation (Figure 2). 

The full 3-D packing arrangement of the nanospheres is revealed by tomographic reconstruction. 

Two distinct types of packing are prevalent in three-layer stacks: cubic-close packed (ccp) and 

hexagonal close-packed (hcp). These two packing arrangements and their differences are 

extensively documented in numerous textbooks (Brandon & Kaplan, 1999). A ccp stacked array 

has sequence of ABCABC..., where A, B, and C represent three distinct, relative layer 

alignments. Bulk ccp stacking generates the face-centered cubic lattice. The hcp structure has 

an ABAB stacking sequence. 

The determination of stacking arrangements is significant in that such self-assembly may 

influence optoelectronic properties. The reconstruction is manipulated to view the layers in 

projection oriented precisely perpendicular to the layers. Slices are then taken through the 

regions of highest density to more clearly reveal the relative positions of NPs within adjacent 

layers. With sufficient refinement of the vertical structure, the arrays can be viewed in crosssection, which would be entirely impossible from a single projection image. 

Figure 2. Cubic close-packed (ccp) and hexagonal close-packed (hcp) stacking 

configurations among size-selected In nanospheres: (a,b) original, 0°-tilt images; (c,d) 

superpositions of three tompographic slices; (e,f) cross-sectional slices taken along the 

diagonal lines shown in c and d. Dotted lines indicate sectioning planes. Dashed lines 

indicate plane of contact with support film. 

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2006 DDRD Annual Report 

The results of this work demonstrate the viability of TEM tomography for analysis of individual 

particle shape and orientation and collective crystallography of nanoparticle ensembles. TEM 

tomography has many potential applications in materials nanoscience. We have shown the direct 

access available to 3-D structural information. However, for crystalline nanoparticles, the 

resolution is limited by diffraction contrast. Although many important questions in the microscopic 

regime can be addressed by conventional bright-field TEM tilt-series tomography, it is anticipated 

that these results could be greatly surpassed using field-emission instruments, with Z-contrast 

imaging capability. Such equipment would be of tremendous value for addressing 3-D 

nanoparticle shapes and configurations. 

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2006 DDRD Annual Report 

Thin-Film Microelectronics for Rapid Gene Expression 

Principal Investigator: Howard Branz 

FY06 Costs: $103,326 

3⁄4The goal of this project is to develop cutting-edge genomics research tools through an 

interdisciplinary effort among NREL semiconductor physicists and microbiologists. The project 

team will research and develop a new type of DNA micro array based on thin-film 

microelectronics technology to accelerate gene expression studies at NREL and elsewhere. The 

research addressed two problems crucial to rapid gene expression assays accelerated by 

application of an electric field: 

• Understanding and control of rapid electric-field enhanced DNA binding and 

hybridization 

• Development of techniques for E-field enhanced detection of complementary DNA 

hybridization in samples containing mixed DNA. 

We deposited and tested several candidate insulating films, and have succeeded in silanizing a 

glass slide coated with an insulating film of electron-beam evaporated silicon dioxide (SiO2). A 

short incubation with a solution containing the precursor molecule (APTES) is sufficient, but it 

appears that a one-hour anneal at about 100o

C is important to form a complete coating. 

Silanization is a notoriously difficult process, but it must be consistently mastered before crosslinker molecules can be attached and DNA can be immobilized on the surface. This silanization 

is confirmed through an FITC-based fluorescence assay of the surface, which we learned from 

our Portuguese colleagues who are working on related problems. Where silanization occurs, we 

see a strong fluorescence signal. 

We have identified a scanning fluorescence instrument at NREL that is allowing more rapid 

characterization of our silanized layers. While the Colorado School of Mine (CSM) fluorescence 

microscope works and is better for fine resolution work, a scanner at NREL will speed up the 

throughput on the project. 

Collaborating with the NREL team is Professor Scott Crowley, CSM Department of Chemistry and 

a post doc experienced in micro-Bioengineering of DNA and proteins. Crowley attends all team 

meetings and has been extremely helpful in the design of experimental cuvettes and 

improvements in chemical functionalization protocols. The CSM group brings expertise in surface 

physical chemistry to the collaboration. 

Next steps include improving washing procedures to remove non-covalently bonded FITC 

molecules that sometimes give a streaky fluorescence signal when we assay even our negative 

silanization controls that were not exposed to APTES. Consistent washing of non-covalent 

molecules is critical. We will also confirm cross-linker attachment to silanized surface, 

immobilization of DNA probes and target hybridization. Then we will complete fabrication of the 

14 
2006 DDRD Annual Report 

E-field apparatus and reproduce literature results. We have designs in progress for time-resolved 

evanescent-field absorption, reflection and fluorescence measurements of hybridization that will 

elucidate the basic mechanisms. 

 

100 ns 

1 V pulse 

Figure 3. Schematic diagram of an electric-field addressed assay for expression of four 

genes. 

15 
2006 DDRD Annual Report 

CdMgTe Thin-Films for Light Emitting Diodes 

Principal Investigators: Ramesh Dhere & Kannan Ramanathan 

FY06 Costs: $199,874 

3⁄4The goal of this project is to prepare cadmium magnesium telluride (CdMgTe) polycrystalline 

thin-films, characterize them, and use them to fabricate light emitting diodes (LED).1⁄2

We achieved the fabrication of polycrystalline Cd(1-x)Mg(x)Te alloy films in a wide composition 

range (up to x = 0.72) which are stable in the normal ambient. To our knowledge, this is the first 

demonstration of CdMgTe films in the polycrystalline form. Polycrystalline thin-films offer a 

number of advantages in terms of cost reduction and capability of large area depositions thus 

widening the scope of the application of these films. Detailed optical characterization of the alloy 

films was performed to establish that the optical band gap of the alloy varies from 1.5 electron volt 

(eV) to 2.7 eV and the transition in this range is direct. In addition, we have been able to cover 

the entire range due to the compositional gradient within the samples. For applications such as 

light emitting diodes, direct band gap semiconductors are essential. CdMgTe alloys are expected 

to be indirect at higher magnesium (Mg) content and determination of the region of direct gap 

transitions is essential for LED applications. The results show that the alloy system can be 

potentially useful in most of the visible spectrum. 

Rectifying junctions of the type glass/ SnO2/ CBD CdS/ CdMgTe were fabricated with alloy 

compositions up to x=0.3. The doping of the films and consequently the resistivity can be 

controlled by post deposition chloride heat treatments. For successful device applications, 

controlled doping and lower resistivities are essential. The doping effect of the treatment shows 

that the electronic properties of these alloys after treatment are good and are comparable to 

CdTe, which has yielded high efficiency solar cells. 

We achieved fabrication of 8% efficient solar cells using CdMgTe alloys with band gap of 1.6 eV. 

We have also fabricated cells with open circuit voltage of 845 mV which is comparable to the 

highest values obtained for cadmium telluride (CdTe) solar cells. Quantum efficiency (QE) of 

these devices is high at longer wavelengths and shows that the performance is affected mainly by 

junction properties which can be improved with further optimization of device processing steps. 

High performance of these devices show that the electronic quality of these CMT alloy films is not 

adversely affected by the addition of Mg to CdTe system. Open circuit voltage is controlled by 

electronic defects in the semiconductor and high voltages achieved in these cells signify lower 

defect densities essential for device applications. The devices prepared from these alloys also 

show excellent electroluminescence (EL) for lower band gap alloys. The EL output of these 

samples is comparable to that of CdTe. High QE at longer wavelengths shows that the diffusion 

length of the minority carriers is high. Good EL response for these alloys shows that they are 

good candidates for LED applications. Solar cells are similar to LEDs in many respects and high 

QE near the band gap for these devices should translate into high performance LEDs. 

NREL is better poised to compete in the solid state lighting arena where LEDs with red, green 

and blue emission are required for white light sources. As CdMgTe alloy system can be tailored 

over a wide range of band gaps, one may be able to fabricate all necessary LEDs from this alloy 

system. Polycrystalline thin-films can be fabricated inexpensively and are suitable for large area 

devices which may allow large area, e.g. whole wall size, light sources. In addition, the alloys in 

the lower band gap range (1.6 eV to 2.2 eV) may be ideal candidates for the development of 

tandem solar cells. 

The remaining task in this project involves the doping of higher band gap alloy system, principally 

over 2 eV. This requires modification of the existing deposition system for incorporation of 

external dopants and experimentation with alternate post deposition treatment. Successful 

controlled doping will enhance the applicability of CdMgTe alloy system. 

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2006 DDRD Annual Report 

Hot-Wire Chemical Vapor Deposition of Metal Oxide Nanorods 

Principal Investigators: Anne Dillon and Harv Mahan 

FY06 Costs: $137,857 

3⁄4The goal of this project is to investigate production of metal oxide nanorods and nanoparticles 

for use in electrochromic windows and batteries.1⁄2

In the first quarter of 2006, in a fashion similar to the procedure used for substoichemetric 

tungsten oxide (WO3) nanoparticle deposition, we have deposited molybdenum oxide (MoO3) 

nanoparticle/nanorod powder having the same lateral dimensions as that for WO3. Using this 

nanoparticle powder as an anode in a lithium battery conjunction, capacities of 1200 mAh/gm 

have been achieved, a value roughly four times higher than that obtained for a standard graphite 

anode. This value lasts for up to 10 cycles. The capacity then slowly degrades after ~20 cycles 

to ~650 milliamp hours/gm (mAh/gm), a value still twice that for a graphite anode. Work is 

underway to understand the stability changes and to reduce them. 

We submitted a Record of Invention (ROI) in the first quarter, which documents the steps used to 

fabricate these highly crystalline, highly porous films. 

A paper entitled ”Crystalline WO3 Nanoparticles for Highly Improved Electrochromic 

Applications”, by S.-H Lee, R. Deshpande, P.A. Parilla, K.M. Jones, B. To, A.H. Mahan, and A.C. 

Dillon, has appeared in Advanced Materials, 18 (2006) 763. 

As the year progressed, porous films containing MoO3 nanoparticles, deposited by hot wire 

chemical vapor deposition (HWCVD), have been incorporated into a lithium ion (Li-ion) battery 

structure as the negative electrode component. We have shown that we can achieve reversible 

capacities (over 50 cycles) as high as 650 mAh/g, a value two times higher than that of 

commercial graphite negative electrodes. This improvement has been achieved by developing 

these small nanoparticles and by coating the nanoparticle films with a thin polymer layer, which 

mitigates mechanical strain issues accompanied by lithium insertion and phase changes. These 

results may become exceedingly important if Li+ battery technologies are to be realized for hybrid 

electric vehicle applications. These advancements could lead to the first demonstration of a solid 

state Li-ion battery which would be suitable for both vehicular and stationary applications. Further 

investigations have been performed to unravel the mechanism of this new phenomena, as our 

results were unanticipated. This greater understanding will lead to publication in a high impact 

journal. 

In addition, the rate capabilities of the anode have been analyzed and shown to be superior to the 

state-of-the-art technologies. A patent application has been filed for this advanced battery 

technology. 

Several publications and presentations have resulted from this research. 

• Thin Solid Films . “Metal Oxide Nanoparticles for Improved Electrochromic and Lithium-Ion 

Battery Technologies” by A.C. Dillon, A.H. Mahan, R. Deshpande, P.A. Parilla, K.M. Jones, 

and S.-H. Lee. (under review). 

• Solid State Ionics . “Optimization of Crystalline Tungsten-Oxide Nanoparticles for Improved 

Electrochromic Applications”, by R. Deshpande, S.-H. Lee, P.A. Parilla, K.M. Jones, B. To, 

A.H. Mahan, J.D Perkins, S. Mitra, and A.C. Dillon, (under review). 

• Electrochemical Society (ECS) proceedings Volume 2, Nanotechnology. “Hot-Wire Chemical 

Vapor Deposition of WO3 and MoO3 Nanoparticles and the Performance of Nanostructured 

WO3 Electrochromic Films”, by R. Deshpande, S.-H. Lee, P.A. Parilla, K.M. Jones, A.H. 

Mahan, B. To, S. Mitra, and A.C. Dillon (in press). 

17 
2006 DDRD Annual Report 

• In addition, we have been invited to submit a journal paper to J. Mater. Chem. “Hot-filament 

Chemical Vapor Deposition of High Density Molybdenum Oxide Nanoparticles”, by R. 

Deshpande, S.-H. Lee, P.A. Parilla, A.H. Mahan, K.M. Jones, S. Mitra, and A.C. Dillon. 

• S.-H. Lee presented a talk on the present LDRD battery work at the annual Electrochemical 

Society Conference, Cancun, Mexico, October 30 – November 3, 2006. 

• A.H. Mahan and A.C. Dillon were on the Organizing Committee and the International program 

Committee respectively, for the 4th International Conference on Hot Wire CVD Process, held 

in Takayama, Japan, October 2006. A paper was presented at the conference that 

summarized our complete DDRD/LDRD work. 

• R. Deshpande received his Ph.D degree from the University of Tulsa. His Ph.D research 

centered exclusively on the work funded by this LDRD project. He has accepted a position in 

industry in California. 

• A proposal entitled “Crystalline Tungsten Oxide Nanoparticles for Photoelectrochemical 

Water Splitting” is part of the NREL/University Mega-Proposal being submitted to the Office 

of Science in the Solar Energy Call. 

This LDRD project has not only generated numerous peer-reviewed papers and high profile talks, 

but has also led to significant progress and the development of new concepts resulting in a patent 

application. Although the proposal submitted jointly with DuPont was not funded, if the NREL 

reviews are positive, it may still be possible to obtain partial funding. As described above, this 

work is also being promoted in the NREL/University mega-proposal. Finally, we have been 

granted additional funding to demonstrate a full battery so as to poise NREL for an upcoming 

battery call. We are exploring the possibility of incorporating our technologies into a solid-state 

battery. This would be a first-time demonstration. 

18 
2006 DDRD Annual Report 

Novel Electron Acceptors for Organic Photovoltaics 

Principal Investigator: David Ginley 

FY06 Costs: $199,009 

3⁄4The goal of this project is to improve hybrid Organic Photovoltaic Cells (OPV) by optimizing the 

nanostructured geometry of the inorganic component and the critical inorganic-organic interface. 

The project combines the expertise of two laboratories to address this key problem in hybrid 

OPV: Sandia National Laboratory (SNL) – inorganics and surfactants; and NREL – polymers, 

oxides and devices. 1⁄2

The laboratories are jointly involved in fabricating samples and devices and understanding the 

nature of the oxide/organic interface. We have purchased and activated a General Purpose 

Capital funded deposition system and have achieved 4% OPV bulk heterojunction cells. By 

integrating the GPE deposition system with our existing capability, our ability to directly address 

the interfacial issues is vastly improved. 

 A clear technical focus has evolved as a result of this joint effort, which is producing state-of-theart results. We anticipate that a number of publications will result from this work. To date a paper 

entitled, “Band Offset Engineering for Enhanced Open Circuit Voltage in Polymer-Oxide Hybrid 

Solar Cells” has been accepted by Advanced Functional Materials and will soon be published. A 

manuscript on dendrimers has also been submitted to Chemical Materials and a paper on 

inverted devices “Inverted bulk-heterojunction organic photovoltaic device using a solutionderived ZnO underlayer” has also been accepted by Applied Physics Letters. In addition we gave 

talks at the Society of Photo-optical Instrumentation Engineers (SPIE) meeting August 7-15 and 

at the MRS meeting November 28-December 1 on the joint project. 

Key personnel are accelerating our device development: Dr. Matt Reece from Yale and two 

graduate students – Matthew White from University of Colorado, Boulder, and Will Rance, from 

Colorado School of Mines. 

This program is new but it is already beginning to show results on the development of improved 

materials for OPV. We anticipate that the increased control of the oxide and interfaces will begin 

to show significant improvements in efficiency. With the advent of the Solar America Initiative, 

this technology will be well positioned in a couple of years to be: incorporated into that program, 

directly transferred to companies, and become a competitive thin film technology. 

19 
2006 DDRD Annual Report 

Nanostructured PbTe/PbSe Thermoelectric Materials 

Principal investigator: Mark Hanna 

FY06 Costs: $78,601 

3⁄4The goal of this project is to develop a process to make a high ZT nanostructured PbTe/PbSe 

thermoelectric material with colloidal precursors that can be scaled up to produce large-area thick 

thermoelectric devices. 1⁄2

This project leveraged existing expertise at NREL in nanoparticles syntheses and materials 

characterization to build a foundation for new research programs in thermoelectric materials. 

These materials may find applications in improving the energy efficiency of vehicles through 

waste heat recovery, direct thermal to electrical energy conversion in solar thermal systems and 

as a fully solid-state heat pump in refrigeration systems. 

 

Our team developed six chemical syntheses for preparing colloidal PbSe and PbTe nanocrystals. 

We thoroughly characterized the nanocrystal product by transmission electron microscopy, 

scanning electron microscopy, Auger electron spectroscopy, e-ray diffraction and thermally 

programmed desorption to identify the particle size, shape, crystallinity, composition and impurity 

content. These synthesis processes are simple, take place at or near room temperature and are 

scalable. 

We developed a synthesis procedure for a single source precursor for the formation of PbSe 

nanocrystals or shells and investigated the synthesis of an analogous single source precursor for 

formation of PbTe. We attempted to produce PbTe/PbSe core-shell nanocrystal samples by 

coating the PbTe nanocrystals with PbSe formed from the single source precursor. This work 

can be used as a starting point for larger scale production of PbTe/PbSe nanoparticles and 

thermoelectric material for future research on thermoelectric materials. 

We deposited films of PbTe nanocrystals by spray deposition which had good thermoelectric 

properties. It shows that good quality thin film thermoelectric material could be produced using 

PbTe nanocrystals. 

We used the technical knowledge gained from this work to assist other divisions at NREL and 

outside companies with their work on thermoelectric materials. I served as technical advisor to 

the Freedom Car and Vehicle Technologies Program for a subcontract on advanced thin-film 

thermoelectric materials at Caterpillar; and assisted Caterpillar engineers in analyzing and 

characterizing their thermoelectric materials. 

The materials synthesis and measurement capabilities that we have developed in the LDRD has 

put NREL in an excellent position to provide assistance to and collaborate with industry and 

possibly obtain new funding from DOE on advanced nanostructured thermoelectric materials. 

Proposed next steps would be to establish a dedicated thermoelectric materials laboratory at 

NREL. It would be an important step in attracting further research funding in this area. 

20 
2006 DDRD Annual Report 

A Critical Examination of the Intermediate Band Concept for 

 Ultra-High Efficiency Quantum Dot Solar Cells 

Principal Investigator: Andrew Norman 

FY06 Costs: $209,717 

3⁄4 The goal of this project is to critically examine, using epitaxially grown quantum dot (QD) super 

lattice (SL) solar cell structures and theoretical modeling, the intermediate band concept that has 

been proposed for ultra high efficiency, lower cost “next” or “third” generation solar cells. This 

work is relevant to NREL’s mission to develop renewable energy and energy efficiency 

technologies and practices, to advance related science and engineering, and to transfer 

knowledge and innovations to address the nation’s energy and environmental goals. It is also 

relevant to DOE’s mission to advance energy technology and promote scientific and technological 

innovation in support of that mission. In particular, this work directly contributes to DOE’s 

Scientific Strategic Goal to advance scientific knowledge and DOE’s Energy Strategic Goal to 

protect our security by promoting a diverse supply and delivery of reliable, affordable, and 

environmentally sound energy.1⁄2

In fiscal year 2006, we accomplished the following: 

• Grew by metal organic oxide chemical vapor deposition (MOCVD) and characterized high 

structural and optical quality 50 period, strain-balanced InGaAs/GaAsP QD SL solar cell 

structures. 

• Achieved 50 period strain-balanced QD SL solar cells with much improved open circuit 

voltages and efficiencies in comparison to non strain-balanced samples. 

• Calculated the excitonic absorption spectra of lens-shaped In0.6GA0.4As/GaAs QDs charged 

with up to three electrons or holes. 

• Obtained first 3D local electrode atom probe (LEAP) data from epitaxially grown III-V QD 

structures in collaboration with Prof. Brian Gorman (University of North Texas) and Imago 

Scientific Instruments. 

• Based on this work, we joined the Defense Advanced Research Projects Agency (DARPA) 

Very High Efficiency Solar Cells (VHESC) project led by the University of Delaware. 

• As a result of this project, two theory papers on carrier relaxation mechanisms and absorption 

transitions in QDs were published by G.A. Narvaez, G. Bester, and A. Zunger in Physical 

Review B. 

• An oral presentation was given at the 2006 Materials Research Society Spring Meeting on 

the MOCVD growth and characterization of strain-balanced InGaAs/GaAsP QD SL solar cell 

structures.

We are now in a great position to supply very high quality strain-balanced QD SL samples for 

further study by Fourier Transform Infrared (FTIR) and time resolved optical techniques. By 

comparing our predictions with (InGa)As/GaAs data on interband absorption and intra-dot 

electron relaxation, we have demonstrated that our theoretical approach reliably predicts 

properties that are relevant to the operation of QD based solar cells. Thus, our approach can be 

applied to predict the properties of other dot/barrier combinations that are better suited as 

intermediate band solar cells. We are also in an excellent position to grow high quality strainbalanced QD SL solar cells to investigate their properties. 

21 
2006 DDRD Annual Report 

The overall impact of the project to NREL in the 

near-term and beyond is high because the 

results obtained are extremely important for 

critically examining the intermediate band 

concept for ultra-high efficiency solar cells. This 

third generation concept, if it is proven, may 

have a significant impact in the future for ultrahigh efficiency solar cells based on both 

epitaxial and colloidal QDs or new materials 

possessing an intermediate band structure. We 

are now better positioned to experimentally and 

theoretically test this concept and to accomplish 

our goal of critically assessing its likelihood of 

success. If the feasibility of the concept is 

demonstrated by this work it will put NREL in a 

much better position to attract future funding. 

Figure 4. Cross-sectional transmission 

electron microscopy image of a strainbalanced InGaAs/GaAsP quantum dot 

superlattice grown by metal organic 

chemical vapor deposition for 

incorporation in a quantum dot solar cell. 

22 
2006 DDRD Annual Report 

Unconventional Indium-Free Transparent Conductors 

Principal Investigator(s): John Perkins and David Ginley 

FY06 Costs: $259,199 

3⁄4 The goal of this project is to find indium-free transparent conductors to replace Indium-Tin–

Oxide (ITO), a material that has increased in price 10-fold over the last two years, and which is 

the current industrial standard. Combinatorial high-throughput composition-spread techniques will 

be used to rapidly survey newly identified candidate transparent conductors (TCOs) outside the 

conventional TCO materials composition space. Subsequent single composition depositions will 

be used to focus on the identified candidate.1⁄2

Transparent conductors are critical to a number of key EERE technologies including PV, windows 

and indoor lighting. The increasing cost of indium coupled with new performance needs is 

creating a renaissance in the TCO area with an increasing focus on new materials. 

Thus far, we have demonstrated that the pulse laser deposited (PLD) based Nb:TiO2 films are 

bulk conductors. The PLD results can be duplicated by sputter deposition and the sputtered film 

on glass are conductive. These results demonstrate that this is a bulk transparent conducting 

material and not an interfacial effect, that it can be deposited by low-cost large-area approaches, 

and that it can be put on amorphous substrates. To date this is the first time that the original 

Japanese results have been duplicated in any laboratory. We have identified that it is truly bulk, 

that it can be sputtered, that anatase is the critical phase and that grain boundaries are important. 

We have submitted out first papers to Applied Physics Letter (APL), Thin Solid Films, and 

Journal of Materials Research (JMR). We have a visiting graduate student from Northwestern 

University who is initiating investigations on the ZnSnOx system by combi techniques. She has 

already duplicated five year old results in this system. This kicked off the combinatorial materials 

development in this new system and will greatly accelerate our program in the time that she is 

here. This has now resulted in a manuscript in preparation in this system. 

This program is showing positive results on the new in free TCO TiO2:Nb. It has clearly 

demonstrated that the effect is real and that the material is viable in single crystal form. Work is 

focusing on improved growth on a variety of substrates and beginning to look at new systems. In 

the coming year, we will focus on evaluating Nb versus Ta by PLD and on exploring the 

deposition and transport films on amorphous substrates. We will continue to investigate the 

ability to dope the ZnSnO3 system and reexamination of the Ga:ZnO system. 

23 
2006 DDRD Annual Report 

Photon Emission of Self-Assembled Semiconducting and 

Quantized Nanostructures by Scanning Tunneling Microscopy: 

Light from the Nanoworld 

Principal Investigator: Manuel Romero 

FY06 Costs: $264,457 

3⁄4The goals of this project are to advance our understanding of nanoscale optoelectronics in selfassembled semiconducting nanostructures, and to develop novel microscopy methods for 

optically detecting and imaging single molecular species (quantum dots, molecular assemblies, 

biomolecules, carbon nanotubes...) based on scanning tunneling microscopy (STM).1⁄2

This project is at the forefront of research in nanoscience and nanotechnology, with potential 

applications in future generations of photovoltaics. We are pioneers in the field of plasmonics – 

exploring the potential applications of combining plasmonics and optoelectronics in light 

concentration and energy conversion. Plasmons (SPs) provide a very attractive and novel 

approach for controlling, manipulating, and amplifying the light in the nanoscale. SPs enable us 

to investigate enhancement effects in the photon absorption and emission of molecular species. 

Plasmonic nanostructures could lead to the fabrication of more efficient light-emitting diodes and 

solar cells. 

We observed that confinement of SPs to the metallic tunneling gap of the STM stimulates the 

emission of light. A quantum dot (QD) found in this optical cavity can be optically detected by the 

extinction of plasmons at the resonant energy. The resonances in the SP spectrum represent a 

fingerprint of the QD and occur at the optical bandgap owing to resonant tunneling through the 

dot. Figure 5 shows the SP spectrum for a series of self-assembled (CdSe)ZnS QDs.)

Figure 5. SP spectrum for a series of self-assembled (CdSe)ZnS QDs.) 

1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0

0

1 QD614

Photon density (103 cps/nA)

Ef,s - Ef,tip (eV)

0

1

QD557

0

1

QD536

0

1

2 QD488

PL

STL

24 
2006 DDRD Annual Report 

Plasmon Resonance Imaging, which is based on the detection of such resonances in the SP 

spectrum, shows a great potential in nanoscale science owing to the combination of the superb 

resolution inherent to STM with the spectroscopy of single molecular species To illustrate the 

potential of this optical microscopy, we have prepared a mulitdot layer combining QDs with 

fluorescence at 536 nm, 557 nm, and 614 nm. Figure 6 shows the plasmon resonance image of 

the multidot structure. 

Figure 6. Plasmon resonance image of the multidot structure. 

In summary, the resonant energies observed in the tunneling SP luminescence spectrum can be 

used to detect single molecular species. We have developed a strategy for detection and 

imaging based on these resonances. This detection and imaging strategy is not restricted to 

quantum dots. It is of great interest to an entire spectrum of nanostructures – from molecular 

assemblies and biomolecules to carbon nanotubes. 

During the second year of this project, we are planning to: (i) control the spectrum of the SP lightsource with metallic nanoparticles; (ii) investigate multilayer and cascade structures of selfassembled quantum dots; and (iii) study the optical response of quantum dots (theoretically and 

experimentally) in the electromagnetic field of SPs. 

100 200 300 400 500

200 nm X (nm)

(a) STM (b) Plasmon resonance

(c) Linescan

(c)

10 nm

25 
2006 DDRD Annual Report 

Low Band Gap Materials for Organic 3rd Generation Photovoltaics 

Principal Investigator: Sean Shaheen 

FY06 Costs: $297,889 

3⁄4The goal of this project is to develop a core competency in the fabrication of organic 

semiconductor based photovoltaic devices that are better optimized to absorb the sun’s 

spectrum. This core competency will also include the facilities and personnel to establish NREL 

as a world-class laboratory in the field. To achieve this we will: develop low band gap materials 

that have optimized transport properties for the use in organic (plastic) photovoltaic (OPV) 

devices; improve the scientific understanding of the structure-property relation of these materials; 

improve the understanding of the physics of the operation of these devices; and develop models 

to guide in their advancement.1⁄2

This project is a cross-center effort utilizing expertise in the National Center for Photovoltaics 

(NCPV), Chemical and Biosciences Center, and the Scientific Computing Center to tackle all 

aspects of molecular design and synthesis, material characterization, and device fabrication. 

Plastic solar cells offer the potential for very low cost and high through-put fabrication at 

reasonable power conversion efficiency. Their development is being aggressively pursued by our 

industrial affiliate Konarka Technologies, in order to bring this technology to full realization. 

Discovery of an optimal low band gap absorber would be rapidly transferred to the marketplace. 

Over the last two years we have developed a new family of molecules, called dendrimers that 

exhibit more desirable fundamental properties, such as purity, molecular ordering, and electronic 

band structure, than existing polymeric semiconductors. Our most promising dendrimer to date 

possesses a lower band gap (1.8 eV) and more optimized band structure than the best polymers 

in the field at the moment. The results obtained so far have helped fuel the emerging OPV effort 

at NREL and have led directly to the initial development of a new characterization technique 

(time-resolved-microwave-conductivity) and device fabrication (a new electrode deposition 

system funded through general purpose equipment. 

We were the first group to report on OPV devices made from dendrimers. They can be 

incorporated into several device geometries, including bulk heterojunction blends with fullerenes 

or nanostructured oxides (see “Novel Electron Acceptors for Organic Photovoltaics” led by David 

Ginley, page 18). 

We have submitted and/or published three papers and given talks at four conferences. 

Papers: 

• Journal of Materials Chemistry, vol.15, 4518 (2005). “The Synthesis and Properties of 

Solution Processable Phenyl Cored Thiophene Dendrimers,” by W.J. Mitchell, N. 

Kopidakis, G. Rumbles, D.S. Ginley, and S. Shaheen (published). 

• Applied Physics Letters, vol. 89, 103524 (2006). “Bulk heterojunction organic photovoltaic 

devices based on phenyl-cored thiophene dendrimers,” by N. Kopidakis, W.J. Mitchell, 

D.S. Ginley, G. Rumbles, S. Shaheen, and W.L. Rance (published). 

• Advanced Functional Materials. “Bulk heterojunctions based on a low band gap 

copolymer of thiophene and benzothiadiazole,” by E. Bungaard, S.E. Shaheen, F.C. 

Krebs, and D. Ginley (submitted). 

• Journal of Materials Chemistry. “The Synthesis and Properties of Soluble Spiral 

Thiophene Dendrimers,” by W.J. Mitchell, N. Kopidakis, A.J. Ferguson, G. Rumbles, D.S. 

Ginley and Shaheen (submitted). 

26 
2006 DDRD Annual Report 

Conferences: 

• American Physical Society March Meeting, Baltimore. “Pi-Conjugated Dendrimers for 

Organic Photovoltaics,” by S.E. Shaheen, W.J. Mitchell, N. Kopidakis, J. Pris, J.J. Bozell, 

G. Rumbles, D.S. Ginley. 

• University of Minnesota iPrime Workshop. “Nanostructured Solution-Processable Organic 

Photovoltaics,” by S.E. Shaheen. 

• Internal Conference on Complex Systems. “Molecular Self-Assembly Processes in 

Organic Photovoltaic Devices, “ by S.E. Shaheen, N. Kopidakis, J. van de Lagemaat, 

W.J. Mitchell, J.Y. Wang, K. Koenig, G. Rumbles, and D.S. Ginley. 

• SPIE Optica and Photonics Conference. “TT-conjugated dendrimers for organic and 

hybrid photovoltaics,” by S.E. Shaheen, N. Kopidakis, W.J. Mitchell, W.L. Rance, D.S. 

Ginley, and G. Rumbles. 

We are attempting to pursue three avenues with the time remaining on the project: 

• Improve the morphology of devices made with materials on hand. 

• Develop even lower band gap materials. 

• Pursue the possibility of a multi-junction OPV device using these materials. 

27 
2006 DDRD Annual Report 

Renewable Fuels Science and Technology 

Localized Carrier Dynamics in Organic Semiconductors Probed via 

Time-Resolved THz Photoconductivity 

Principal Investigator: Randy Ellingson 

FY06 Costs: $209,850 

3⁄4The goal of this project is to develop time-resolved terahertz (THz) photoconductivity (TRTP) for 

application to organic molecular crystals as well as to other systems consisting of colloidal 

semiconductor quantum dot, polymeric, and/or molecular absorbers. We expected to extract 

detailed information about the mechanisms and dynamics of charge separation and transport in 

organic semiconductors.1⁄2

Developing expertise in the measurement and characterization of charge carrier dynamics in 

organic semiconductors and related materials supports NREL’s mission to advance the science 

related to efficient solar energy production. On a microscopic scale, solar energy conversion 

begins with the absorption of a photon to generate a photoexcited state. The evolution of the 

photoexcited state over the first ~1 ns largely determines the potential for converting the photon’s 

energy to electricity or to fuels. Time-resolved THz photoconductivity (TRTP) represents a 

unique experimental probe for monitoring the production of charge carriers on the ultra fast 

timescale without the need to attach wires. The TRTP technique is ideally suited for 

measurements of dynamics of free carrier generation and recombination in several complicated 

solar cell systems, such as the increasingly important “blended bulk heterojunction” device 

design. 

We have been striving to develop TRTP for investigating organic semiconductors. We have 

successfully demonstrated the applicability of TRTP to systems consisting of combinations of 

conjugated polymers, C60 metallofullerenes, and inorganic semiconductor QD. These 

measurements have revealed important details about the mechanisms for conversion of photons 

to free charge carriers in a polymer/C60 “blended heterojunction” design, including how the free 

carrier yield varies with C60 concentration. Substantial additional value continues as the TRTP 

technique has now been successfully applied to the characterization of local conductivity in QD 

arrays. The results of the project have been presented at the Materials Research Society (MRS) 

meeting in San Francisco. A manuscript titled: “Photoinduced Charge Carrier Generation in a 

Poly(3-hexylthiophene) and Methanofullerene Bulk Heterojunction Investigated by Time-Resolved 

Terahertz Spectroscopy” (by Ai, X.; Beard, M.; Knutsen, K.; Shaheen, S.; Rumbles, G.; and 

Ellingson, R.) has also been accepted to the Journal of Physical Chemistry for publication. 

Preparation of the polymer-C60 manuscript represents a major accomplishment as it addresses 

the highly complicated response of the bulk heterojunction organic solar cell to photoexcitation 

within the solar spectrum. The manuscript describes a number of important processes believed 

to occur in such devices, including exciton generation, exciton-exciton annihilation, bound polaron 

(electron-hole pairs with one carrier on each of two neighboring polymer chains) generation, free 

carrier (polaron) generation, and trapping. 

The results include a discussion of the mechanisms leading to varying performance 

characteristics, including the relative quantum yield of free carriers, as a function of the device 

composition (varying the PCBM C60 weight fraction over values of 0.0, 0.2, 0.5, 0.8, and 1.0). 

TRTP spectroscopy is uniquely sensitive to the conduction mechanism in low conductivity 

materials and is thus poised to make a significant contribution to the understanding of these 

important photo-conversion materials. Measuring charge carrier dynamics (e.g., generation, 

relaxation, and recombination) is critical to the development of novel materials and device 

designs for photo-production of electricity/fuels. 

28 
2006 DDRD Annual Report 

Application of the TRTP technique will be used to study exciton dissociation in organic 

semiconductors and other so-called “excitonic” solar cells. TRTP and accompanying analysis 

tools will be utilized to determine exciton diffusion rates, the yield of free carriers, the dynamics of 

interfacial recombination, and doping densities in organic semiconductors developed here at 

NREL. 

29 
2006 DDRD Annual Report 

Transition Metal Catalysis: Experiment and Theory 

Principal Investigator: Mark Nimlos 

FY06 Costs: $193,014 

3⁄4 The goal of this project is to demonstrate that high level quantum mechanical calculations can 

be useful in guiding the development of hydrogenolysis catalysts. We propose to use a close 

collaboration between laboratory measurements and quantum mechanical molecular modeling to 

improve our understanding of catalytic processes that are important in renewable energy 

production and utilization. In this project we will develop hydrogenolysis catalysts that are 

capable of converting alcohols into alkanes. 1⁄2

Hydrogenolysis catalysts that are capable of converting alcohols into alkanes are a novel 

chemical process that is thermodynamically favored but seldom observed. This reaction will be 

useful in upgrading the energy content of a variety of biomass derived materials. From a broader 

perspective, it would introduce a new simple approach to a chemical transformation that is usually 

quite difficult. Novel complexes have been developed at NREL that should be capable of 

catalyzing this hydrogenolysis reaction. The focus of this project is to demonstrate that the 

catalytic hydrogenolysis of alcohols is feasible, and perhaps more important, to demonstrate that 

high level of quantum mechanical calculations can be useful in guiding the development of these 

catalysts. 

Our accomplishment involved: 

• Demonstrating formation of key palladium and platinum hydride intermediates in the 

presence of strong acids. 

• Demonstrating catalytic hydrogenolysis of the model substrate benzyl alcohol to toluene 

using a palladium catalyst. 

• Obtaining trends for changes in energies of molecular orbitals with changing bite angle. 

• Calculating accurate moleclular geometried for palladium complexes. 

• Calculating accurate relative hydricities for palladium complexes. 

This represents the first example of designed metal hydride catalysts that are formed by reaction 

with hydrogen and are both stable in strong acid and capable of delivering the hydride ligand to a 

substrate to form a C-H bond. This is not only important for biomass hydrogenolysis, but can 

have a significant impact on fuel cell catalysis and for the utilization of hydrogen as a reductant. 

The success of our calculations gives us confidence to extend these to other potential catalysts. 

Next, we propose to: 

• Move from model substrate benzyl alcohol to glycerol 

• Study catalysis in ionic liquid solvents 

• Prepare more active platinum-based catalysts. 

• Write a paper on calculations. 

30 
2006 DDRD Annual Report 

Pentose Transport and Assay Development 

Principal Investigator: Min Zhang 

FY06 Costs: $164,884 

3⁄4 The goal of this project is to establish methodologies to study structure and function 

relationships of xylose transport proteins. We also propose to establish rapid and reliable assays 

for analysis of the kenetics of sugar transport. 1⁄2

Xylose is the second most abundant sugar available in the world and could potentially produce 

one third of the ethanol from plant biomasss feedstocks. Microbial utilization of xylose suffers 

from its low utilization rate and low product yield. Xylose transport through the cell membrane is 

first step in xylose utilization. Efficient utilization of xylose is the key to economical production of 

liquid transportation fuels form biomass feedstocks. This is critically important to EERE’s 

strategic goals to reduce dependence on foreign oil and to create a bioindustry based on 

biorefineries. Efficient utilization of xylose, the second most abundant sugar in the world, could 

tremendously expand the biomass industry. 

During this project we: 

• Established xyIE expression system for functional analysis. This is an essential step for 

the study of xyIE function. 

• Developed a growth assay method for screening of xyIE function, which enables large 

scale analysis. 

• Conducted site-directed mutagenesis using alanine scanning and mutant 

characterization. These activities allow functional characterization of the role of individual 

amino acids in xyIE. 

• Identified 11 amino acids were that are irreplaceable for xyIE’s active uptake sugar 

function. These results will be used to prepare a manuscript for submission to peerreview journals. 

• Obtained a xyIE mutant with significantly higher xylose transport activity and improved 

affinity. This unique mutant could be useful to improve biomass to ethanol process and 

has a potential for technology transfer to ongoing industry biorefinery projects. 

Efficient xylose utllization is critical to the economical production of liquid transportation fuels from 

biomass feedstocks. The work potentially supports DOE goals in creating a bioindustry and 

reducing dependence on petroleum. 

31 
2006 DDRD Annual Report 

Fundamental Properties and Applications of Novel Crystalline 

Inorganic-Organic Hybrid Semiconductors 

Principal Investigator: Yong Zhang 

FY06 Costs: $190,047 

3⁄4 The goal of this project is to obtain and understand the basic structural, electronic, and optical 

properties of the hybrid crystals.1⁄2 

We are collaborating with researchers at Rutgers University and have succeeded in making films 

of hybrid materials with conductive polymers by spin-coating; and we are performing optical and 

electric measurements on these films. The success in depositing hybrid films is the first step for 

making these materials useful in device applications. We have been collaborating with 

researchers at Advanced Photon Source at Argonne National Laboratory (APS/ANL) in the study 

of the unusual thermal expansion of the hybrid crystals. We finished the thermal expansion 

measurements for all the three crystal axes for the hybrid crtstal beta-ZnTe(en)0.5, in our second 

trip to APS/ANL. The complete structure of the thermal expansion of the novel hybrid material 

was obtained – at least for one type of structure. After the experimental data are carefully 

analyzed, we will write a paper important to this field. The theoretical results for the phonon 

spectrum of the hybrid crystal beta-ZnTe(en)0.5 were obtained in the collaboration with 

researchers at the University of Arkansas. The phonon spectrum is critical for us to understand 

the unusual Raman results we obtained a while ago, and the thermal expansion that is closely 

related to the temperature dependence of the phonon modes. 

In addition to collaborating with Rutgers University and 

the University of Arkansas, we continue to collaborate 

with the University of Colorado (CU), Boulder, 

Chemistry Department on the x-ray study of hybrid 

crystals. The CU collaboration provides 

complimentary measurements to those conducted at 

ANL. The collaboration with these groups has 

benefited all of us and significantly advanced our 

understanding of the new hybrid materials. 

As the principal investigator, I was invited to give talks 

at: ANL/APS Users Scientific Seminar in August 2006; 

and the CU Physics Department Condensed Matter 

Seminar in September 2006. I presented a poster at 

the CU-NREL symposium, and co-PI Brian Fluegel 

presented a poster with me at the NREL LDRD poster 

review session. 

Through these presentations, interest in these new 

hybrid materials is growing, particulary in in low dimensionality, 2D and 1D, for potential 

thermoelectricity applications. 

Figure 7. Beyond Nano: an array 

of sub-nanometer quantum wires. 

Our research has revealed that this new family of organic-inorganic crystals exhibit unusual 

properties in a larger number of aspects than we had anticipated, which offers many exciting 

opportunities for both fundamental studies and applications. Our effort has positioned NREL at 

the very frontier of this new exciting field, and improved the chance for us to receive outside 

funding so we can broaden the scope of our research. 

Moving forward we plan to perform more theoretical and experimental studies on hybrid crystals 

with lower dimensionalities (2D and 1D), and will continue the effort of making n- or p-type doping 

and studying the conductivity for hybrid crystals. 

32 
2006 DDRD Annual Report 

Prototype Renewable Planning Model (RPM) 

Principal Investigator: Ben Kroposki 

FY06 Costs: $258,271 

3⁄4 The goal of this project is to develop a preliminary assessment tool, the Renewable Planning 

Model (RPM), to integrate basic resource availability (i.e. solar irradiation, wind resource, and 

biomass feedstocks) with infrastructure elements (i.e. power distribution system, roads) and 

constraints onto a single geographic interface.1⁄2

In 2005, we: created a basic Web-based geographic information system (GIS) map viewer and an 

interface with HOMER program; received distribution system load data from Xcel Energy; and 

added an overlay capability to GIS mapper. In 2006, we: delved into detailing imagery – adding 

high resolution (1ft) imagery to select areas; started a NREL repository of high resolution imagery 

data; and performed PVWatts hourly simulation for a specified PV system. PVWatts is accessible 

as a Web-based service for external instances of the RPM tool. We also performed hourly load 

analysis and added access to sample power distribution feeder hourly loads through load versus 

time, load-simulation versus time, peak load day, and load versus hours-at-load (load duration 

curve). The tool now allows both large-scale (regional) and small-scale (individual buildings) 

basic siting analysis. The tool demonstrates “end-to-end” capability with a few selected areas 

and detailed data sets. This serves as a solid base upon which to build and integrate more 

advanced capability. 

We have “system creation on map” capability – tools to draw and simulate a system on top of 

detailed imagery. Aggregation of individual systems into groups of systems, and further 

aggregation of groups into larger groups allows users to begin using the tool for broader areas 

and larger scale analysis. This is another baseline functionality that will serve as a base for 

higher level functionality. There is an internet visible application of the RPM on Linux using 

Apache and a local Postgres database. It is authenticated with a Digest based user/password, 

and NREL’s IS team has performed acceptance tests. Internet visible versions of RPM allow 

easy access and broad distribution possibilities. The current server will only support small 

concurrent user loads, but that may be sufficient for the near future. 

Imagery from Denver International Airport (DIA), distribution data (lines, transformers, switch 

points, etc), and hourly load data obtained from Xcel has been loaded onto the system for Xcel 

visible Web pages. We separated a different version of the RPM configuration into separate Web 

URL’s and modified the code to allow easy URL creation as a way to make customized or 

specialized versions of RPM. For example, a “wind relevant” site that shows wind class, hides 

solar layers. We also have simulations using actual data in the Denver area, based on SRRL 

data for 2004/2005, thereby expanding the simulation data source to both “typical” and “actual” 

(i.e., typical metrological year and measured data). Simulations based on actual data allow a 

user to see more than just a composite data set, and allows relevant comparisons to actual load 

data for specific years. Browser support was expanded to include Microsoft’s Internet Explorer. 

This provides for much wider accessibility. Wind relevant data layers were expanded and a more 

manageable slope exclusion layer was added. Expanding wind layers enable RPM to begin a 

“Community Wind” assessment project with Xcel. Initial distance buffering functionality was 

added to RPM to expand dynamic GIS functionality. 

Initial integration to HOMER as a wind simulation engine via Web service call to remote server 

was completed to add extensive system modeling and analysis functionality. We assembled 

Hydrogen relevant GIS layers into grouping for a Hydrogen Assessment (HyDRA) spin-off project, 

and added a variance graph for Solar resource over 30 years. This will graphically show best and 

worse case over long periods of time and aid in the understanding of solar for mid-level users. 

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2006 DDRD Annual Report 

The project has received reasonably high external and internal visibility. All external feedback has 

been extremely positive. We demonstrated the project to members of Xcel’s chief corporate 

officers: NREL executive management including the laboratory director, and a local 

congressman. We are working to turn this into resources and partnerships for continued project 

development. RPM has been shown to Xcel’s distribution planning and several members of the 

Amendment 37 compliance team. We also presented to the Xcel Utility Innovations group. Xcel 

accepted our proposal for some high-value short term functional extensions and is considering 

our longer term proposal for a next phase. Since the prototype has been shown to most all 

relevant audience within NREL, we are now doing demonstrations over the Web to possible users 

for additional exposure and idea gathering. The users include system integrators and utility 

based renewable planners. It broadens our exposure to other possible partners outside 

Colorado. 

Xcel expressed interest in an alternate direction so we did additional strategic analysis and 

submitted a different proposal addressing functionality that will meet both NREL and Xcel 

strategic direction. This includes simulating 95% probably power levels and creating 

characteristic areas to allow aggregation over larger areas. We also created a project branch to 

show HyDRA in an interactive GIS framework. HyDRA will provide additional leverage for the 

current prototype system. 

A distributed development environment (which includes live demonstrating, source code 

management, and remote PVWatts simulation model access) allows current [Xcel] and future 

partners to work interactively with project code base and models. The Xcel development helped 

to accelerate our initial schedule by at least six months. 

We were able to demonstrate RPM to anyone with access to the internet through WebEx, an 

internet based meeting/demonstration system setup. This greatly expands our ability to show the 

prototype without travel expenses. Internet accessibility allows us to send links to potential 

users/reviewers and let them use the tool when it is convenient for them. This gives us much 

broader exposure and global accessibility. 

Overall, the project is now pushing additional “wind based” functionality in to the tool. This will 

broaden the use of RPM and expand the pool of possible users. From a technical standpoint, we 

have integrated two additional NREL applications and have started reinforcing integration 

infrastructure needed to bring in additional models. We will push for expanded integration with 

HOMER to generalize our distributed generation functionality, and to pursue more complete wind 

simulation functionality. 

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2006 DDRD Annual Report 

Appendix A: Acronyms and Symbols 

ANL – Argonne National Laboratory 

APL – Applied Physics Letter 

APS – Advanced Photon Source 

APTES – 3-Aminopropyltriethoxysilane 

BD – Brownian Dynamics 

CBD – Chemical Bath Deposit 

CdMgTe – Cadmium Magnesium Telluride 

CdS – Cadmium Sulfide 

CdTe – Cadmium Telluride 

CSM – Colorado School of Mines 

CU – Colorado School of Mines 

DARPA – Defense Advance Research 

Projects Agency 

DDRD – Director’s Discretionary Research 

and Development (program) 

DIA – Denver International Airport 

DOE – Department of Energy 

ECS – Electrochemical Capacitor Society 

EERE – Energy Efficiency and Renewable 

Energy 

EL – Electroluminescence 

[FeFe]-hydrogenase – Iron-Iron 

hydrogenase (hydrogenase containing 

the two Iron metal cluster) 

FTIR – Fourier Transform Infrared 

FITC – fluorescein isothiocyanate

FNR - Flavin-nicotine amide dinucleotide 

phosphate (NADP+) oxidoreductase 

Ga – Galium 

GPE – General Purpose Equipment 

H

2 

– Hydrogen 

JAP – Journal of Applied Physics 

JMR – Journal of Materials Research 

LDO – Laboratory Development Office 

LEAP – Local Electrode Atom Probe 

LEDs – Light Emitting Diodes 

Li – Lithium 

Li-ion – Lithium Ion 

mAh/gm – Milliamp Hours/gm 

Mg - Magnesium 

MOCVD – Metal Oxide Chemical Vapor 

Deposition 

MoO3 – Molybdenum Oxide 

MM – Molecular Mechanical 

MRS – Materials Research Society 

Nb – Niobium 

NCPV – National Center for Photovoltaics 

NP – Nanoparticle 

OPV – Organic Photovoltaic 

PbSe – Lead Selenide 

PbTe – Lead Telluride 

PCBM – (C60 is the most common carbon 

buckyball, and when functionalized as: [6,6]-

phenyl C61-butyric acid methyl ester; it’s 

commonly referred to as PCBM.) 

PLD – Pulse Laser Deposit 

PV – Photovoltaics 

QE – Quantum Efficiency 

QD – Quantum Dot 

QM - Quantum Mechanical 

QM/MM - [combined] Quantum Mechanical 

and Molecular Mechanical

ROI – Record of Invention 

RPM – Renewable Planning Model 

SC – Solid State 

SD&A – Strategic Development and 

Analysis 

SiO2 – Silicon Dioxide 

SL – Super Lattice 

Sn – Tin 

SnO2 – Tin Oxide 

SP – Plasmon 

SPIE – Society of Photo-optical 

Instrumentation Engineers 

SRRL – Solar Radiation Resource Lab 

STM – Scanning Tunneling Microscopy 

TCO – Transparent Conductors 

TEM – Transmission Electron Microscopy 

THz – Terahertz 

TRTP – Time Resolved Terhertz 

Photoconductivity

TiO2 – Titanium Dioxide 

TMY – Typical Meteorological Year 

VHESC – Very High Efficiency Solar Cells 

WFO – Work for Others 

WO3 – Substoichemetric (The W is not fully 

oxidized.) 

Zn – Zinc 

ZT – (A dimensionless figure of merit for 

thermoelectric materials. ZT=S

2

σT/k – S is 

the Seebeck coefficient, σ is the electrical 

conductivity, k is thermal conductivity, and T 

is the temperature.) 

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