The Solar Energy Technologies Program primarily funds research to further develop commercially attractive photovoltaic technologies. It is also useful for the SETP to fund temporary projects that explore new ideas. If the new concepts are successful, the efforts may be expanded; if they are unsuccessful, then they should be terminated to free those funds for new projects.

U.S. Department of Energy’s Solar Energy Technologies Program (SETP) focuses research, development, and deployment projects and activities in two technology areas: Photovoltaics (PV) and Concentrating Solar Power (CSP). The Solar Program has initiated the Technology Pathway Partnerships (TPPs), the PV Technology Incubator programs, and the PV Next Generation programs, which are executing the Solar America Initiative by working with industry, national laboratories, universities, and other members of the solar energy community..

The PV Next Generation Program represents an important early stage government investment in exploratory researches and development of innovative and highly disruptive PV technologies, which are expected to produce prototype PV cells and processes by 2015, with full commercialization by 2020-2030. The specific projects of the PV Next Generation Program are detailed below.

1.   Transfer Printed Microcells with Micro-Optic Concentrators for Low Cost, High Performance Photovoltaic Modules (University of Illinois/Wakonda Technologies) Transfer printing to distribute large numbers (>250,000) of GaAs microcells with molded, micro-optic concentrators over large area foreign substrates, interconnected with direct ink writing.

2.  Thin, High Lifetime Silicon Wafers with No Sawing; Recrystallization in a Thin Film Capsule (MIT) - To create a silicon wafer-making technology that will set a new standard by combining high electronic quality and low cost.

3.   High Aspect Ratio Semiconductor Heterojunction Solar Cells (PennsylvaniaStateUniversity) - Photovoltaic devices made from radial single junction a-Si/nc-Si nanowires grown on inexpensive substrates like glass.

4.     Culn (Ga) Se2 (CIGS) Nanowire Solar Cells (StanfordUniversity): Production of inorganic nanostructured thin film solar cells made of CIGS nanowires with diameters less than 200 nm.

5.    Next Generation CdTe Technology Substrate Foil- Based Solar Cells (University of South Florida): To transform the standard process/product design of CdTe cells and modules from a glass-to-glass superstrate configuration, into a metallic foil substrate configuration using close- spaced sublimation, a high throughput process.

6.    Feasibility Demonstration and Performance Optimization of a Disruptive Ultra-High-Efficiency, Thin-Film, Crystalline Silicon Solar Cell for Cost- Effective, Grid-Connected Electricity (Soltaix): Use of thin film Si absorber layer for high-efficiency cells with efficient light trapping and reduced Si usage. The technical approach removes dependency of cell manufacturing on the traditional Si wafer supply chain.

7.   II-IV-V Based Thin Film Tandem Photovoltaic Cell (ArizonaStateUniversity): Development of materials for II-IV-V based tandem thin film cells, starting with ZnSnP2 and ZnGeAs₂ , to push 20% efficiency.

8.    All-Inorganic, EfficientPhotovoltaicSolidState Devices Utilizing Semiconducting Colloidal Nanocrystal Quantum Dots (University of Delaware): Tunable bandgap using Cd or Pb quantum dots. Tandem devices are made by putting quantum dots on top of a conventional cell or mechanically stacking quantum dot cells with different bandgaps. Solution processible for low cost photovoltaics.

9.   Novel Approaches to Wide Bandgap CuInSe2 -Based Solar Cells (MIT): Development of a highly efficient, wide bandgap, CuInSe2 chalcopyrite-based solar cell, which is necessary for polycrystalline tandem devices. Laser processing will be used to control defects, which will improve the performance of the cell (Advanced Thin Films – Tandem Cells).

10.  Advanced Semiconductor Materials Breakthrough Photovoltaic Applications (ArizonaStateUniversity): To demonstrate the fundamental viability of new semiconductor materials with a potential for disruptive breakthroughs in photovoltaics (High Efficiency Multi-Junction Cells).

11.  Very High Efficiency Hybrid Organic-Inorganic Photovoltaic Cells (University of Florida): Aligned, inorganic ternary alloy nanorods with tuned bandgaps combined with organic polymer hole conduction media arranged in tandem devices. Solution processible for low cost photovoltaics (Hybrid Organic/Inorganic).

12.   High Efficiency Nanostructured III-V Photovoltaics for Solar Concentrators Application (Rochester Institute of Technology): InAs quantum dots incorporated into the GaAs cell of a multijunction III-V device to enhance IR absorption in the near term and provide initial insight into intermediate band cells in the long term (Intermediate Bands).

13.  Exciton Fission for an Ultra-High Efficiency, Low Cost Solar Cell (University of Colorado): Graetzel cell that will use dye molecules and nanocrystals of dye to produce multiple electrons from one photon of light (Multiple Exciton Generation).

14.  Optimization of Impact Ionization in Composite Nanocrystal Photovoltaic Devices (Voxtel): “Janus” nanoparticles incorporated in conducting polymer cells will use multiple exciton generation to go beyond conventional limits in power production (Multiple Exciton Generation).

15. High Efficiency Quantum Dot Solar Cells Based on Multiple Exciton Generation (Solexant): To demonstrate that the efficient multiple exciton generation observed in quantum dot materials can be harvested in nanostructured solar cells to dramatically improve the maximum power efficiency obtainable in photovoltaic modules (Multiple Exciton Generation).

16.  Functional Multi-layer Solution Processable Polymer Solar Cells (University of California, Davis): Organic photovoltaics made from of multiple polymer films with electron- only, hole-only and interface dipole layers. A gel protection layer allows for spin coating of the multiple polymer films. Solution processible for low cost photovoltaics.

17.  Crystalline Organic Photovoltaic Cells (University of Michigan): Organic, small molecule planar hetero- junction, tandem cells utilizing the crystalline physical form.

18.  Interfacial Engineering for Highly Efficient π-Conjugated Polymer-Based Bulk Heterojunction Photovoltaic Devices (University of Washington): Devices with 10nm interdigitated organic nanostructures, where self assembled electroactive molecules will improve performance by reducing interface recombination. Multilayer, solution processible tandem cells are the ultimate goal.

19.  Solar Cells from Earth-Abundant Semiconductors with Plasmon-Enhanced Light Absorption (California Institute of Technology): Plasmonic light absorption in earth-abundant semiconductors (quantum dots, and Zn3P2 ).  A top cell with earth abundant absorber will be integrated with a Si bottom cell.

20.  High-Efficiency Photovoltaics Based on Semiconductor Nanostructures (University of California, San Diego): Researchers will produce high- efficiency photovoltaics that combine plasmonics and III-V quantum well and nanowire solar cells.

21.  Improved Electrodes and Electrolytes for Dye-Based Solar Cells (PennsylvaniaStateUniversity): Graetzel cell with polyphosphazene polymer gel electrolyte, used in lithium ion batteries, intercalated between TiO2 columns (Sensitized Cells).

22. Nanostructured Materials for High Efficiency Low Cost Solution-Processed Photovoltaics (StanfordUniversity): Ordered ZnO nanowire networks or Ag nanowire meshes for low cost contacts. Solution processing into ordered networks through bubble expansion of nanowire/polymer suspension (Si Synthesis).

23.  Solar Grade Silicon from Agricultural By-Products (Mayaterials): Polysilicon solar cell feedstock derived from agricultural by-product streams without the Siemens process. With anticipated energy contents and production costs equal to or lower than conventional methods. Target cost: < $25/kg (Si Synthesis)

24.  High Efficiency Solar Power via Separated Photo and Voltaic Pathways (Solasta): Nanostructures of carbon nanotubes, PV absorber material (a-Si), and metal to make nanoengineered solar cells, which separates the path of the photons from the path of the generated charge carriers. Milestone: 25% efficiency by 2010 (Si Synthesis).

25.  Organic Photovoltaics OPV (NREL): Excitonic solar cells, which rely on exciton dissociation at a donor-acceptor interface to create carriers, have recently reached certified solar efficiencies of 5%.  Improvements in material quality, device design, and understanding of the device physics are necessary to further improve cell efficiencies.  

26.  Sensitized Solar Cells (NREL): Sensitized solar cell (DSSC) – has reached certified efficiencies >11% for laboratory cells and 6%–7% for modules. However, certain environmental conditions greatly increase degradation and efficiency in cells. The design and development of more effective materials (sensitizers, nanostructured films, charge-conducting phases, conducting substrates) and cell configurations and the assessment of cell stability at different cell efficiency levels will constitute a significant fraction of the research effort. Both organic/inorganic hybrids and entirely inorganic versions of sensitized solar cells will be developed.

27.  Wafer Silicon Photovoltaics (NREL): As the Si-PV industry grows further, it faces challenges to further lower the PV energy cost, increase throughput and conversion efficiencies, and improve reliability (longer life expectancy) of solar modules. This project will target new methods of crystal growth, new cell designs, and Si solar cell process development. These are in the areas of novel device design that are not only capable of higher efficiency but simpler to fabricate, novel processes such as optical processing, device process modeling, characterization, and diagnostic technologies for Si-PV manufacturing.

Major solar electricity research activities will be aimed at paving the scientific foundation to drive a revolution in the way that the next of generation solar cells are conceived, designed, implemented, and manufactured.  These breakthroughs will come from a broad range of research activities in both materials and device topologies. They include 1) single-crystal, polycrystalline, amorphous, and nanostructured inorganic and organic materials; 2) understanding of the electronic structure of these materials; and 3) implementation in single and multiple junction solar cells to take advantage of optical shifting, multiple exciton generation and hot carrier generation. These projects are expected to last 3 years and to overlap with projects funded by EERE’s Solar Program.  

Another government agency, the Defense Advance Research Projects Agency (DARPA; a central research and development organization for the Department of Defense), is developing high efficiency PV devices based on multijunction cell technology. In February 2005, DARPA’s Advanced Technology Office issued a solicitation for up to $53 million for Very High Efficiency Solar Cell (VHESC) program.

In late July 2007, a consortium led by the University of Delaware (UD) announced that it had created a solar cell with a conversion rate of 42.8%. They employed an optical system that splits sunlight into three components while concentrating it by about a factor of 20. Three separate solar cells – made by NREL, UD, and Emcore Corporation - convert each piece of the solar spectrum into electricity to achieve the record conversion efficiency. Unlike the typical concentrating solar cell, the new device features optics that are less than one centimeter thick and that accept sunlight from a wide range of angles, allowing the device to be mounted in a fixed position. Based on the success of this effort, DARPA announced recently the start of a new three-year effort to drive efficiency to more than 50%.

Collaboration with other government offices and departments extends beyond basic research. With solar cell efficiencies above 40% today, a different Department of Defense group is re-exploring the potential for satellite-based solar power stations to meet future energy needs by beaming power to military locations around the world.

Meeting the solar market cost goals will result in 5-10 GW of PV installed by 2015 in the U.S. and 70-100 GW by 2030. For CSP, satisfaction of these cost targets is expected to lead to installation of between 16 and 35 GW of new generating capacity by 2030.

The major solar energy program activities include:

·   Photovoltaics Research and Development (R&D) to achieve impactful improvements in the cost, reliability, and performance of devices, components, and systems.

·   Concentrating Solar Power R&D to develop and improve utility-scale power systems and to create and demonstrate effective storage technologies.

·   Market Transformation to reduce market barriers through non-R&D activities, including infrastructure development and deployment assistance.

·    Partnerships with Other Programs to effectively accelerate the commercialization of solar energy systems and to integrate results of basic research results from other government programs into solar program R&D activities.

By Vasil Sidorov on April 20, 2009 after U.S. Department of Energy’s Solar Energy Technologies Multi Year 2008-2012 Program