Douglas Kirkpatrick

50% Efficient Solar Cell Architectures and Designs

Very high efficiency solar cells (VHESC) for portable applications that operate at greater than 55 percent efficiency in the laboratory and 50 percent in production are being created. We are integrating the optical design with the solar cell design, and have entered previously unoccupied design space that leads to a new paradigm. This project requires us to invent, develop and transfer to production these new solar cells. Our approach is driven by proven quantitative models for the solar cell design, the optical design and the integration of these designs. We start with a very high performance crystalline silicon solar cell platform. Examples will be presented. Initial solar cell device results are shown for devices fabricated in geometries designed for this VHESC program

Nanostructured Solar Cells for High Efficiency Photovoltaics

The use of nanostructures in photovoltaics offers the potential for high efficiency by either using new physical mechanisms or by allowing solar cells which have efficiencies closer to their theoretical maximum, for example by tailoring material properties. At the same time, nanostructures have potentially low fabrication costs, moving to structures or materials which can be fabricated using chemically or biologically formed materials. Despite this potential, there are multiple and significant challenges in achieving viable nanostructured solar cells, ranging from the demonstration of the fundamental mechanisms, device-level issues such as transport mechanisms and device structures and materials to implement nanostructured solar cells, and low cost fabrication techniques to implement high performance designs. This paper presents the challenges and approaches for using nanostructured solar cells in devices which can approach the thermodynamic limits for solar energy conversion

Very high efficiency solar cells

The Defense Advanced Research Projects Agency has initiated the Very High Efficiency Solar Cell (VHESC) program to address the critical need of the soldier for power in the field. Very High Efficiency Solar Cells for portable applications that operate at greater than 55 percent efficiency in the laboratory and 50 percent in production are being developed. We are integrating the optical design with the solar cell design, and have entered previously unoccupied design space that leads to a new architecture paradigm. An integrated team effort is now underway that requires us to invent, develop and transfer to production these new solar cells. Our approach is driven by proven quantitative models for the solar cell design, the optical design and the integration of these designs. We start with a very high performance crystalline silicon solar cell platform. Examples will be presented. Initial solar cell device results are shown for devices fabricated in geometries designed for this VHESC Program.

Darpa's Push for Photovoltaics

The Defense Advanced Research Projects Agency has initiated the Very High Efficiency Solar Cell (VHESC) program to address the critical need of the soldier for power in the field. A range of technological breakthroughs from fields outside the normal contributors to photovoltaic technology development have enabled the consideration of new design and manufacturing paradigms. An integrated team effort is now underway to develop 50% efficient solar cells over the next three to four years, culminating in the fabrication and delivery of 1000 prototype 0.5 W, 10 cm2 modules

Optimal design of a bifurcated refractive coupler for the HEDlight program

In this contribution we consider the problem of designing coupling optics to optimally transfer light from a metal-halide arc lamp to a large core polymethyl methacrylate (PMMA) fiber optic cable. We investigate a refractive optical coupling concept comprising a non-axisymmetric bifurcated refractive glass TIR lens (TIRL) set. The design goal is to maximize the photometric flux incident onto two 19-mm-diameter apertures within an acceptance half angle of 38º. The light source is an 80-Watt metal halide arc lamp, characterized by means of photometric data measured by Radiant Imaging. The lenses each comprise a central refractive section combined with an annular TIR section. The exit pupil of each TIR lens is separated from the entrance aperture of the target by a short air gap. The refractive section of the TIR lens utilizes two aspheric surfaces to collect source flux over a central solid-angular region and redirect it into the target. The TIR section utilizes a total of three aspheric surfaces, two of which are refractive and one of which is a TIR surface. To account for right-left asymmetries in the optical source, the TIR lenses were independently globally optimized for both sides. Our TIRL design has the advantage of being able to collect and control radiation emanating at both large and small angles from the source, with little overall loss. The TIRL, with an ideal AR coating, has a predicted coupling efficiency of 89.6%. This was accomplished even though the target to source etendue ratio is only 63.7%. This is possible due to the ability of this design to preferentially transfer radiation from the higher radiance portions of the source phase space to the target. The work described above was funded by the Defense Advanced Research Projects Agencys High Efficiency Distributed Lighting Program known as HEDLight.